Bacteria are classified according to their shape. Bacteria, their diversity

Classification of bacteria by shape.

Based on their shape, all bacteria are divided into 3 groups:

Globular or cocci

Rod-shaped or sticks

Twisted shapes of bacteria.

Cocci have a round, spherical, oval, candle-flame, lanceolate shape and are divided into 6 subgroups based on the connection method.

1 micrococci;

2 diplococci;

3 tetracocci;

4 streptococci;

5 staphylococci;

6 sarcinas.

All cocci are immobile and do not form spores.
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Widely distributed in nature. Included in fermented milk starters. May be pathogenic (angina, gonorrhea, meningitis).

Rod-shaped bacteria have an elongated shape. Length is greater than width. They easily change their shape based on living conditions, ᴛ.ᴇ. have polymorphism. Rods are the most common group of all bacteria. They may not be pathogenic, but can cause various diseases (typhoid, dysentery).

Rods can be mobile or immobile, forming or not forming spores. Based on their ability to form spores, rods are divided into three groups:

Bacteria;

bacilli;

Clostridia.

The convoluted forms of bacteria are divided into three groups:

1. vibrios;

2. spirilla;

3. spirochetes.

All convoluted forms are pathogenic.

Structure and functions of the cell membrane of bacteria.

Cell membrane covers the outside of the cell. It is a dense, elastic structure that can withstand differential pressure, consisting of two parts - an outer part called the cell wall and an inner part - the cytoplasmic membrane (CPM). Both the wall and the membrane have pores (holes) through which nutrients pass into the cell and waste products are removed. In this case, nutrients pass through the pores of the cell wall with a molecular weight of no more than 1000, ᴛ.ᴇ. During feeding, the wall acts as a mechanical sieve. Nutrients pass through the pores of the CPM not by mass, but as needed, ᴛ.ᴇ. it is semi-permeable.

The cell membrane performs a number of important functions:

1 – maintains body shape;

2 – protects the cell from external influences;

3 – participates in cell metabolism, ᴛ.ᴇ. allows nutrients to pass through and excretes waste products;

4 – participates in cell movement. Bacteria deprived of a cell membrane lose mobility;

5 – participate in the formation of the capsule.

Classification of bacteria by shape. - concept and types. Classification and features of the category "Classification of bacteria by shape." 2017, 2018.

Determination of their pathogenicity. For example, the likelihood of developing a disease when Staphylococcus aureus is detected in the blood is much higher than when Staphylococcus epidermidis is present. Some bacteria (for example, Corynebacterium diphtheriae and Vibrio cholerae) cause serious illness and have the ability to spread epidemically. Methods for identifying bacteria are based on their physico-immunological or molecular properties.

Gram stain: The sensitivity of gram-positive and gram-negative antibiotics varies. Some other microorganisms (eg mycobacteria) require different staining methods to identify them.

Form: cocci, rods or spirals.

Endospores, their presence and location in the bacterial cell (terminal, subterminal or central).

Relation to oxygen: Aerobic microorganisms require oxygen to exist, while anaerobic bacteria are able to survive in an environment with little or no oxygen content. Facultative anaerobes can live both in the presence of oxygen and without it. Microaerophiles multiply rapidly in low oxygen partial pressures, while capnophiles multiply in environments with high CO2 content.

Demandingness: Some bacteria require special culture conditions to grow.

Essential enzymes(enzymatic activity): for example, a lack of lactose in the medium indicates the presence of Salmonella, and the urease test helps to identify Helicobacter.

Serological reactions arise when antibodies interact with the surface structures of bacteria (some types of Salmonella, Haemophilus, meningococci, etc.).

Sequence of bases in DNA: The key element in bacterial classification is 168-ribosomal DNA. Despite the universality of the above parameters, it should be remembered that they are to a certain extent relative and in practice they sometimes show significant variability (for example, intraspecific differences, interspecific similarities). Thus, some strains of E. coli sometimes cause diseases with a clinical picture similar to infections caused by Shigella sonnei; and the clinical picture of diseases caused by toxigenic strains of C. diphtheriae differs from that of infections caused by non-toxigenic forms.

Medically significant species of bacteria

Gram-positive cocci:
- staphylococci (catalase-positive): Staphylococcus aureus, etc.;
- streptococci (catalase-negative): Streptococcus pyogenes, which causes sore throat, pharyngitis and rheumatic fever; Streptococcus agalactiae, which causes meningitis and pneumonia in newborns.

Gram-negative cocci: Neisseria meningitidis (causative agent of meningitis and septicemia) and N. Gonorrhoeae [causative agent of urethritis (gonorrhea)].

Gram-negative coccobacilli: pathogens of respiratory diseases (genus Haemophilus and Bordetella), as well as zoonoses (genus Brucella and Pasteurella).

Gram-positive bacilli They are divided into spore-forming and non-spore-forming bacteria. Spore-forming bacteria are divided into aerobic (Bacillus genus, for example, Bacillus anthracis, which causes anthrax) and anaerobic (Clostridium spp., they are associated with diseases such as gas gangrene, pseudomembranous colitis and botulism). Non-spore-forming bacteria include the genera Listeria and Corynebacterium.

Gram-negative rods: facultative anaerobes of the Enterobacteriaceae family (opportunistic representatives of the normal microflora of humans and animals, as well as microorganisms often found in the environment). The most famous representatives of the group are bacteria of the genera Salmonella, Shigella, Escherichia, Proteus and Yersinia. Recently, antibiotic-resistant strains of the genus Pseudomonas (saprophytes widely distributed in the environment) have increasingly emerged as causative agents of nosocomial infections. Under certain conditions, Legionella living in the aquatic environment can become pathogenic for humans.

Spiral shaped bacteria:
- small microorganisms of the genus Helicobacter that affect the human gastrointestinal tract and cause gastritis, gastric and duodenal ulcers (in some cases, stomach cancer);
- pathogens of acute diarrhea;
- bacteria of the genus Borrelia, causing epidemic relapsing fever (B. duttoni, B. recurrentis); chronic diseases of the skin, joints and central nervous system; Lyme disease (B. burgdorferi);
- microorganisms of the genus Leptospira, related to zoonoses, causing acute meningitis, accompanied by hepatitis and renal failure;
- genus Treponema (causative agent of syphilis T. pallidum).

Rickettsia, Chlamydia and Mycoplasma. The use of artificial nutrient media is only possible for growing bacteria of the genus Mycoplasma, while to isolate microorganisms of the genera Rickettsia and Chlamydia, it is necessary to use cell culture or special molecular and serological methods.

2.2. Classification and morphology of bacteria

Classification of bacteria. The decision of the International Code for bacteria recommended the following taxonomic categories: class, division, order, family, genus, species. The species name corresponds to binary nomenclature, i.e. it consists of two words. For example, the causative agent of syphilis is written as Treponema pallidum. The first word is na-

the name of the genus and is written with a capital letter, the second word denotes the species and is written with a lowercase letter. When a species is mentioned again, the generic name is abbreviated to the initial letter, for example: T.pallidum.

Bacteria are prokaryotes, i.e. prenuclear organisms, since they have a primitive nucleus without a shell, nucleolus, or histones. and the cytoplasm lacks highly organized organelles (mitochondria, Golgi apparatus, lysosomes, etc.)

In the old Bergey Manual of Systematic Bacteriology, bacteria were divided according to the characteristics of the bacterial cell wall into 4 divisions: Gracilicutes - eubacteria with a thin cell wall, gram-negative; Firmicutes - eubacteria with a thick cell wall, gram-positive; Tenericutes - eubacteria without a cell wall; Mendosicutes - archaebacteria with a defective cell wall.

Each department was divided into sections, or groups, based on Gram staining, cell shape, oxygen demand, motility, metabolic and nutritional characteristics.

According to the 2nd edition (2001) of the ManualBergey, bacteria are divided into 2 domains:"Bacteria" and "Archaea" (Table 2.1).

Table. Domain characteristicsBacteriaAndArchaea

*Among thin-walled gram-negative eubacteria distinguish:

spherical forms, or cocci (gonococci, meningococci, veillonella);

convoluted forms - spirochetes and spirilla;

rod-shaped forms, including rickettsia.

** To thick-walled gram-positive eubacteria include:

spherical forms, or cocci (staphylococci, streptococci, pneumococci);

rod-shaped forms, as well as actinomycetes (branching, filamentous bacteria), corynebacteria (club-shaped bacteria), mycobacteria and bifidobacteria (Fig. 2.1).

Most gram-negative bacteria are grouped into the phylum Proteobacteria. based on similarity in ribosomal RNA “Proteobacteria” - named after the Greek god Proteus. taking on various forms). They appeared from common photosynthesis tic ancestor.

Gram-positive bacteria, according to the studied ribosomal RNA sequences, are a separate phylogenetic group with two large subdivisions - with a high and a low ratio G+ C (genetic similarity). Like the Proteobacteria, this group is metabolically diverse.

To domain "Bacteria» includes 22 types, from whichThe following are of major medical importance:

TypeProteobacteria

Class Alphaproteobacteria. Childbirth: Rickettsia, Orientia, Ehrlichia, Bartonella, Brucella

Class Betaproteobacteria. Childbirth: Burkholderia, Alcaligenes, Bordetella, Neisseria, Kingella, Spirillum

Class Gammaproteobacteria. Childbirth: Francisella, Legionella, Coxiella, Pseudomonas, Moraxella, Acinetobacter, Vibrio, Enterobacter, Callimatobacterium, Citrobacter, Edwardsiella, Erwinia, Escherichia, Hafnia, Klebsiella, Morganella, Proteus, Providencia, Salmonella, Serratia, Shigella, Yersinia, Pasteurella

Class Deltaproteobacteria. Genus: Bilophila

Class Epsilonproteobacteria. Childbirth: Campylobacter, Helicobacter, Wolinella

TypeFirmicutes (mainwaygrampolo­ resident)

Class Clostridia. Childbirth: Clostridium, Sarcina, Peptostreptococcus, Eubacterium, Peptococcus, Veillonella (Gram-negative)

Class Mollicutes. Genera: Mycoplasma, Ureaplasma

Class Bacilli. Childbirth: Bacillus, Sporosarcina, Listeria, Staphylococcus, Gemella, Lactobacillus, Pediococcus, Aerococcus, Leuconostoc, Streptococcus, Lactococcus

TypeActinobacteria

Class Actinobacteria. Childbirth: Actinomyces, Arcanodacterium, Mobiluncus, Micrococcus, Rothia, Stomatococcus, Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, Bifidobacterium, Gardnerella

TypeClamydiae

Class Clamydiae. Childbirth: Clamydia, Clamydophila

TypeSpirochaetes

Class Spirochaetes. Childbirth: Spirochaeta, Borrelia, Treponema, Leptospira

Phylum Bacteroidetes

Class Bacteroidetes. Childbirth: Bacteroides, Porphyromonas, Prevotella

Class Flavobacteria. Childbirth: Flavobacterium

The division of bacteria according to the structural features of the cell wall is associated with the possible variability of their coloring in one color or another using the Gram method. According to this method, proposed in 1884 by the Danish scientist H. Gram, depending on the staining results, bacteria are divided into gram-positive, stained blue-violet, and gram-negative, stained red. However, it turned out that bacteria with the so-called gram-positive type of cell wall (thicker than that of gram-negative bacteria), for example, bacteria of the genus Mobiluncus and some spore-forming bacteria, instead of the usual gram-positive color, have a gram-negative color. Therefore, for the taxonomy of bacteria, the structural features and chemical composition of cell walls are of greater importance than Gram staining.

2.2.1. Shapes of bacteria

There are several main forms of bacteria (see Fig. 2.1) - coccoid, rod-shaped, convoluted and branching, filamentous forms of bacteria.

Spherical forms, or cocci,- spherical bacteria 0.5-1.0 microns in size*, which, according to their relative positions, are divided into micrococci, diplococci, streptococci, tetracocci, sarcinae And staphylococci.

Micrococci(from Greek micros - small) - separately located cells.

Diplococcus(from Greek diploos - double), or paired cocci, are located in pairs (pneumococcus, gonococcus, meningococcus), since the cells do not separate after division. Pneumococcus (the causative agent of pneumonia) has a lanceolate shape on opposite sides, and gonococcus(the causative agent of gonorrhea) and meningococcus (the causative agent of epidemic meningitis) have the shape of coffee beans, with their concave surface facing each other.

Streptococci(from Greek streptos - chain) - round or elongated cells that form a chain due to cell division in the same plane and the preservation of the connection between them at the site of division.

Sarcins(from lat. sarcina - bunch, bale) are arranged in the form of packages of 8 or more cocci, since they are formed during cell division in three mutually perpendicular planes.

Staphylococcus(from Greek staphyle - bunch of grapes) - cocci, arranged in the form of a bunch of grapes as a result of division in different planes.

Rod-shaped bacteria differ in size, shape of cell ends and relative position of cells. The length of the cells varies from 1.0 to 10 µm, thickness - from 0.5 to 2.0 µm. The rods can be regular (E. coli, etc.) and irregular (corynebacteria And other) forms, including branching ones, for example, in actinomycetes. The smallest rod-shaped bacteria include rickettsia.

The ends of the rods can be cut off (anthrax bacillus), rounded (Escherichia coli), pointed (fusobacteria) or in the form of a thickening. In the latter case, the rod looks like a club (Corynebacterium diphtheria).

The slightly curved rods are called vibrios (Vibrio cholerae). Most rod-shaped bacteria are arranged randomly because the cells move apart after dividing. If after cell division the cells remain connected,

If they share common fragments of the cell wall and do not diverge, they are located at an angle to each other (Corynebacterium diphtheria) or form a chain (anthrax bacillus).

Twisted Shapes- spiral-shaped bacteria, for example spirilla, having the appearance of corkscrew-shaped convoluted cells. Pathogenic spirilla includes the causative agent sodoku (rat bite disease). The convoluted ones also include Campilobacter and Helicobacter, which have bends like the wing of a flying seagull; bacteria such as spirochetes are also close to them. Spirochetes- thin, long, crimped

spiral-shaped) bacteria that differ from spirilla in mobility due to flexural changes in cells. Spirochetes consist of an outer membrane

cell wall) surrounding a protoplasmic cylinder with a cytoplasmic membrane and an axial filament (axistyl). The axial filament is located under the outer membrane of the cell wall (in the periplasm) and, as it were, twists around the protoplasmic cylinder of the spirochete, giving it a helical shape (primary curls of the spirochete). The axial filament consists of periplasmic fibrils - analogues of bacterial flagella and is a contractile protein flagellin. The fibrils are attached to the ends of the cell (Fig. 2.2) and are directed towards each other. The other end of the fibrils is free. The number and arrangement of fibrils varies among species. Fibrils are involved in the movement of spirochetes, giving the cells rotational, bending and translational motion. In this case, spirochetes form loops, curls, and bends, which are called secondary curls. Spirochetes

do not accept dyes well. They are usually painted according to Romanovsky-Giemsa or silver plated. Live spirochetes are examined using phase-contrast or dark-field microscopy.

Spirochetes are represented by 3 genera that are pathogenic for humans: Treponema, Borrelia, Leptospira.

Treponema(genus Treponema) have the appearance of thin, corkscrew-twisted threads with 8-12 uniform small curls. Around the protoplast of the treponema there are 3-4 fibrils (flagella). The cytoplasm contains cytoplasmic filaments. Pathogenic representatives are T.pallidum - the causative agent of syphilis, T.pertenue - causative agent of the tropical disease yaws. There are also saprophytes - inhabitants of the human oral cavity and the silt of reservoirs.

Borrelia(genus Borrelia), unlike treponemas, they are longer, have 3-8 large curls and 7-20 fibrils. These include the causative agent of relapsing fever (IN.recurrentis) and the causative agents of Lyme disease (IN.burgdorferi and etc.).

Leptospira(genus Leptospira) They have shallow and frequent curls - in the form of a twisted rope. The ends of these spirochetes are curved like hooks with thickenings at the ends. Forming secondary curls, they take on the appearance of letters S or with; have 2 axial filaments (flagella). Pathogenic representative L. in­ terrogans causes leptospirosis when ingested with water or food, leading to the development of hemorrhages and jaundice.

in the cytoplasm, and some in the nucleus of infected cells. They live in arthropods (lice, fleas, ticks) that are their hosts or carriers. Rickettsia received its name from H. T. Ricketts, an American scientist who first described one of the pathogens (Rocky Mountain spotted fever). The shape and size of rickettsia may vary (irregular, filamentous cells) depending on growth conditions. The structure of rickettsia does not differ from that of gram-negative bacteria.

Rickettsia have a metabolism independent of the host cell, however, it is possible that they receive high-energy compounds from the host cell for their reproduction. In smears and tissues they are stained according to Romanovsky-Giemsa, according to Macchiavello-Zdrodovsky (rickettsia are red, and infected cells are blue).

In humans, rickettsiae cause epidemic typhus. (Rickettsia prowazekii), tick-borne rickettsiosis (R. sibirica), Rocky Mountain spotted fever (R. rickettsii) and other rickettsioses.

Elementary bodies enter the epithelial cell by endocytosis with the formation of an intracellular vacuole. Inside the cells, they enlarge and transform into dividing reticular bodies, forming clusters in vacuoles (inclusions). Elementary bodies are formed from reticular bodies, which leave the cells by exocytosis or cell lysis. Those who left

Elementary body cells enter a new cycle, infecting other cells (Fig. 16.11.1). In humans, chlamydia causes damage to the eyes (trachoma, conjunctivitis), urogenital tract, lungs, etc.

Actinomycetes- branching, filamentous or rod-shaped gram-positive bacteria. Its name (from Greek. actis - Ray, mykes - fungus) they received due to the formation of drusen in the affected tissues - granules of tightly intertwined threads in the form of rays extending from the center and ending in flask-shaped thickenings. Actinomycetes, like fungi, form mycelium - thread-like intertwining cells (hyphae). They form substrate mycelium, which is formed as a result of cell ingrowth into the nutrient medium, and aerial mycelium, which grows on the surface of the medium. Actinomycetes can divide by fragmentation of the mycelium into cells similar to rod-shaped and cocci-shaped bacteria. On the aerial hyphae of actinomycetes, spores are formed that serve for reproduction. Actinomycete spores are usually not heat-resistant.

A common phylogenetic branch with actinomycetes is formed by the so-called nocardi-like (nocardioform) actinomycetes, a collective group of rod-shaped, irregularly shaped bacteria. Their individual representatives form branching forms. These include bacteria of the genera Corynebacterium, Mycobacterium, Nocardianjxp. Nocardi-like actinomycetes are distinguished by the presence in the cell wall of the sugars arabinose, galactose, as well as mycolic acids and large amounts of fatty acids. Mycolic acids and cell wall lipids determine the acid resistance of bacteria, in particular Mycobacterium tuberculosis and leprosy (when stained according to Ziehl-Neelsen, they are red, and non-acid-resistant bacteria and tissue elements, sputum are blue).

Pathogenic actinomycetes cause actinomycosis, nocardia - nocardiosis, mycobacteria - tuberculosis and leprosy, corynebacteria - diphtheria. Saprophytic forms of actinomycetes and nocardia-like actinomycetes are widespread in the soil, many of them are producers of antibiotics.

Cell wall- a strong, elastic structure that gives the bacterium a certain shape and, together with the underlying cytoplasmic membrane, “restrains” the high osmotic pressure in the bacterial cell. It is involved in the process of cell division and transport of metabolites, has receptors for bacteriophages, bacteriocins and various substances. The thickest cell wall is found in gram-positive bacteria (Fig. 2.4 and 2.5). So, if the thickness of the cell wall of gram-negative bacteria is about 15-20 nm, then in gram-positive bacteria it can reach 50 nm or more.

Mycoplasmas- small bacteria (0.15-1.0 µm), surrounded only by a cytoplasmic membrane. They belong to the class Mollicutes, contain sterols. Due to the absence of a cell wall, mycoplasmas are osmotically sensitive. They have a variety of shapes: coccoid, filamentous, flask-shaped. These forms are visible during phase-contrast microscopy of pure cultures of mycoplasmas. On a dense nutrient medium, mycoplasmas form colonies that resemble fried eggs: a central opaque part immersed in the medium and a translucent periphery in the form of a circle.

Mycoplasmas cause atypical pneumonia in humans (Mycoplasma pneumoniae) and lesions of the genitourinary tract (M.homi- nis and etc.). Mycoplasmas cause diseases not only in animals, but also in plants. Non-pathogenic representatives are also quite widespread.

2.2.2. Bacterial cell structure

The structure of bacteria has been well studied using electron microscopy of whole cells and their thin sections, as well as other methods. The bacterial cell is surrounded by a membrane consisting of a cell wall and a cytoplasmic membrane. Under the shell is protoplasm, consisting of cytoplasm with inclusions and a nucleus called the nucleoid. There are additional structures: capsule, microcapsule, mucus, flagella, pili (Fig. 2.3). Some bacteria are capable of forming spores under unfavorable conditions.

In the cell wall of gram-positive bacteria contains small amounts of polysaccharides, lipids, and proteins. The main component of the cell wall of these bacteria is multilayer peptidoglycan (mu-rein, mucopeptide), accounting for 40-90% of the mass of the cell wall. Teichoic acids (from the Greek. teichos - wall), the molecules of which are chains of 8-50 glycerol and ribitol residues connected by phosphate bridges. The shape and strength of bacteria is given by the rigid fibrous structure of the multilayer peptidoglycan, cross-linked with peptides.

Peptidoglycan is represented by parallel molecules glycan. consisting of repeating N-acetylglucosamine and N-acetylmuramic acid residues connected by a glycosidic bond. These bonds are broken by lysozyme, which is an acetylmuramidase. Glycan molecules are linked through N-acetylmuramic acid by a four-amino acid peptide cross-link ( tetrapeptide). Hence the name of this polymer - peptidoglycan.

The basis of the peptide bond of peptidoglycan in gram-negative bacteria is tetrapeptides consisting of alternating L- and D-amino acids, for example: L-alanine - D-glutamic acid - meso-diaminopimelic acid - D-alanine. U E.coli (gram-negative bacterium) peptide chains are connected to each other through D-alanine of one chain and meso-diaminopimeli-

new acid - another. The composition and structure of the peptide part of the peptidoglycan of gram-negative bacteria is stable, in contrast to the peptidoglycan of gram-positive bacteria, the amino acids of which may differ in composition and sequence. Peptidoglycan tetrapeptides in gram-positive bacteria are connected to each other by polypeptide chains of 5 residues

glycine (pentaglycine). Instead of meso-diamino-pimelic acid, they often contain lysine. Glycan elements (acetylglucosamine and acetylmuramic acid) and tetra-peptide amino acids (meso-diaminopimelic and D-glutamic acids, D-alanine) are a distinctive feature of bacteria, since they are absent in animals and humans.

The ability of Gram-positive bacteria to retain gentian violet in combination with iodine when stained using Gram stain (blue-violet color of bacteria) is associated with the property of multilayer peptidoglycan to interact with the dye. In addition, subsequent treatment of a bacterial smear with alcohol causes a narrowing of the pores in the peptidoglycan and thereby retains the dye in the cell wall. Gram-negative bacteria lose the dye after exposure to alcohol, which is due to a smaller amount of peptidoglycan (5-10% of the cell wall mass); they are discolored with alcohol and, when treated with fuchsin or safranin, acquire a red color.

IN composition of the cell wall of gram-negative bacteria enters the outer membrane, connected via lipoprotein to the underlying layer of peptidoglycan (Fig. 2.4 and 2.6). When viewed by electron microscopy of ultrathin sections of bacteria, the outer membrane has the appearance of a wavy three-layer structure, similar to the inner membrane, which is called cytoplasmic. The main component of these membranes is a bimolecular (double) layer of lipids.

The outer membrane is a mosaic structure represented by lipopolysaccharides, phospholipids and proteins. Its inner layer is represented by phospholipids, and the outer layer contains lipopolysaccharide(LPS). Thus, the outer membrane is asymmetrical. The outer membrane LPS consists of three fragments:

lipid A - a conservative structure, almost the same in gram-negative bacteria;

core, or core, crustal part (lat. core - core), relatively conserved oligosaccharide structure;

a highly variable O-specific polysaccharide chain formed by repeating identical oligosaccharide sequences.

LPS is “anchored” in the outer membrane by lipid A, which causes the toxicity of LPS and is therefore identified with endotoxin. The destruction of bacteria by antibiotics leads to the release of large amounts of endotoxin, which can cause endotoxic shock in the patient. The core, or core part, of LPS extends from lipid A. The most constant part of the LPS core is keto-deoxyoctonic acid (3-deoxy-O-man-no-2-octulosonic acid). The O-specific chain extending from the core part of the LPS molecule determines the serogroup, serovar (a type of bacteria detected by immune serum) of a particular strain of bacteria. Thus, the concept of LPS is associated with the concept of O-antigen, by which bacteria can be differentiated. Genetic changes can lead to defects, “shortening” of bacterial LPS and the resulting “rough” colonies of R-forms.

The matrix proteins of the outer membrane permeate it in such a way that protein molecules called porins border hydrophilic pores through which water and small hydrophilic molecules with a relative mass of up to 700 Da pass.

Between the outer and cytoplasmic membrane there is a periplasmic space, or periplasm, containing enzymes (proteases, lipases, phosphatases,

nucleases, beta-lactamases), as well as components of transport systems.

When the synthesis of the bacterial cell wall is disrupted under the influence of lysozyme, penicillin, protective factors of the body and other compounds, cells with a modified (often spherical) shape are formed: protoplasts - bacteria completely devoid of a cell wall; spheroplasts are bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, i.e., acquire a full cell wall and restore their original shape.

Bacteria of the sphero- or protoplast type, which have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to reproduce, are called L-forms (from the name of the D. Lister Institute, where they were first studied). L-forms can also arise as a result of mutations. They are osmotically sensitive, spherical, flask-shaped cells of various sizes, including those passing through bacterial filters. Some L-forms (unstable), when the factor that led to changes in bacteria is removed, can reverse, “returning” to the original bacterial cell. L-forms can be produced by many pathogens of infectious diseases.

Cytoplasmic membrane ana in electron microscopy of ultrathin sections, it is a three-layer membrane (2 dark layers, each 2.5 nm thick, separated by a light intermediate one). In structure (see Fig. 2.5 and 2.6) it is similar to the plasmalemma of animal cells and consists of a double layer of lipids, mainly phospholipids, with embedded surface and integral proteins that seem to penetrate through the structure of the membrane. Some of them are permeases involved in the transport of substances.

The cytoplasmic membrane is a dynamic structure with mobile components, so it is thought of as a mobile fluid structure. It surrounds the outer part of the bacterial cytoplasm and is involved in the regulation of osmotic pressure.

niya, transport of substances and energy metabolism of the cell (due to enzymes of the electron transport chain, adenosine triphosphatase, etc.).

With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complex twisted membrane structures, called mesosomes. Less complexly twisted structures are called intracytoplasmic membranes. The role of mesosomes and intracytoplasmic membranes is not fully understood. It is even suggested that they are an artifact that occurs after preparing (fixing) a specimen for electron microscopy. Nevertheless, it is believed that derivatives of the cytoplasmic membrane participate in cell division, providing energy for the synthesis of the cell wall, and take part in the secretion of substances and sporulation, i.e., in processes with high energy consumption.

The cytoplasm occupies the main volume of the bacterial cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes, responsible for the synthesis (translation) of proteins.

Bacterial ribosomes have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to SOS ribosomes characteristic of eukaryotic cells. Therefore, some antibiotics, by binding to bacterial ribosomes, inhibit bacterial protein synthesis without affecting protein synthesis in eukaryotic cells. Bacterial ribosomes can dissociate into two subunits - 50S and 30S. Ribosomal RNAs (rRNAs) are conserved elements of bacteria (the “molecular clock” of evolution). 16S rRNA is part of the small ribosomal subunit, and 23S rRNA is part of the large ribosomal subunit. The study of 16S rRNA is the basis of gene systematics, allowing one to assess the degree of relatedness of organisms.

The cytoplasm contains various inclusions in the form of glycogen granules, polysaccharides, beta-hydroxybutyric acid and polyphosphates (volutin). They accumulate when there is an excess of nutrients in the environment and

They act as reserve substances for nutrition and energy needs.

Volutin has an affinity for basic dyes and is easily detected using special staining methods (for example, Neisser) in the form of metachromatic granules. With toluidine blue or methylene blue, volutin is stained red-violet, and the cytoplasm of the bacterium is stained blue. The characteristic arrangement of volutin granules is revealed in the diphtheria bacillus in the form of intensely stained cell poles. Metachromatic staining of volutin is associated with a high content of polymerized inorganic polyphosphate. Under electron microscopy, they look like electron-dense granules 0.1-1.0 microns in size.

Nucleoid- equivalent to the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, closed in a ring and tightly packed like a ball. The nucleus of bacteria, unlike eukaryotes, does not have a nuclear envelope, nucleolus and basic proteins (histones). Typically, a bacterial cell contains one chromosome, represented by a DNA molecule closed in a ring. If division is disrupted, 4 or more chromosomes can converge in it. The nucleoid is detected in a light microscope after staining using DNA-specific methods: Feulgen or Romanovsky-Giemsa. In electron diffraction patterns of ultrathin sections of bacteria, the nucleoid appears as light zones with fibrillar, thread-like structures of DNK bound in certain areas to

cytoplasmic membrane or mesoso-

mine, involved in chromosome replication (see Fig. 2.5 and 2.6).

In addition to the nucleoid, represented by one

chromosome, in a bacterial cell there are

extra-chromosomal factors of heredity -

plasmids (see section 5.1.2.) representing

are covalently closed rings of DNA.

Capsule, microcapsule, mucus . Capsule-

a mucous structure more than 0.2 microns thick, firmly associated with the cell wall of bacteria and having clearly defined external boundaries. The capsule is visible in fingerprint smears from pathological material. In pure cultures of bacteria, a capsule is formed

less often. It is detected using special methods of staining a smear according to Burri-Gins, which creates a negative contrast of the substances of the capsule: ink creates a dark background around the capsule.

The capsule consists of polysaccharides (exopolysaccharides), sometimes polypeptides; for example, in the anthrax bacillus it consists of polymers of D-glutamic acid. The capsule is hydrophilic and contains a large amount of water. It prevents the phagocytosis of bacteria. Capsule antigen-na: Antibodies against the capsule cause it increase (swelling reaction and I capsule ly).

Many bacteria form a microcapsule - a mucous formation less than 0.2 microns thick, detectable only by electron microscopy. Mucus should be distinguished from the capsule - mucoid exopolysaccharides that do not have clear external boundaries. Mucus is soluble in water.

Mucoid exopolysaccharides are characteristic of mucoid strains of Pseudomonas aeruginosa, often found in the sputum of patients with cystic fibrosis. Bacterial exopolysaccharides are involved in adhesion (sticking to substrates); they are also called glyco-

calix. In addition to the synthesis of exopolysaccharides by bacteria, there is another mechanism for their formation: through the action of extracellular bacterial enzymes on disaccharides. As a result, dextrans and levans are formed.

The capsule and mucus protect bacteria from damage and drying out, since, being hydrophilic, they bind water well and prevent the action of the protective factors of the macroorganism and bacteriophages.

Flagella bacteria determine the mobility of the bacterial cell. Flagella are thin filaments originating from the cytoplasmic membrane and are longer than the cell itself (Fig. 2.7). The thickness of the flagella is 12-20 nm, length 3-15 µm. They consist of 3 parts: a spiral filament, a hook and a basal body containing a rod with special disks (1 pair of disks in gram-positive bacteria and 2 pairs in gram-negative bacteria). Flagella are attached to the cytoplasmic membrane and cell wall by discs. This creates the effect of an electric motor with a rod - a rotor - rotating the flagellum. The proton potential difference on the cytoplasmic membrane is used as an energy source. The rotation mechanism is provided by proton ATP synthetase. The rotation speed of the flagellum can reach 100 rps. If a bacterium has several flagella, they begin to rotate synchronously, intertwining into a single bundle, forming a kind of propeller.

Flagella consist of a protein - flagellin (from. flagellum - flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are twisted in a spiral.

The number of flagella in bacteria of various species varies from one (monotrichus) in Vibrio cholerae to tens and hundreds of flagella extending along the perimeter of the bacterium (peritrichus) in Escherichia coli, Proteus, etc. Lophotrichus have a bundle of flagella at one end of the cell. Amphitrichy has one flagellum or a bundle of flagella at opposite ends of the cell.

Flagella are detected using electron microscopy of preparations sprayed with heavy metals, or in a light microscope after treatment with special methods based on etching and adsorption of various

substances leading to an increase in the thickness of flagella (for example, after silvering).

Villi, or drank(fimbriae) - thread-like formations (Fig. 2.7), thinner and shorter (3 + 10 nm x 0.3 + 10 µm) than flagella. The pili extend from the cell surface and are composed of the protein pilin. They have antigenic activity. There are pili responsible for adhesion, i.e., for attaching bacteria to the affected cell, as well as pili responsible for nutrition, water-salt metabolism, and sexual (F-pili), or conjugation pili.

Pili are usually numerous - several hundred per cell. However, she usually has 1-3 sexual saws per cell: they are formed by the so-called “male” donor cells containing transmissible plasmids (F-, R-, Col plasmids). A distinctive feature of the sex pili is their interaction with special “male” spherical bacteriophages, which are intensively adsorbed on the sex pili (Fig. 2.7).

Controversy- a peculiar form of resting bacteria with a gram-positive type of cell wall structure (Fig. 2.8).

Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.). A single spore (endospore) is formed inside a bacterial cell. The formation of spores contributes to the preservation of the species and is not a method of reproduction, like in fungi.

Spore-forming bacteria of the genus Bacillus, y whose spore size does not exceed the diameter of the cell are called bacilli. Spore-forming bacteria in which the size of the spore exceeds the diameter of the cell, which is why they take the shape of a spindle, are called clostridia, for example bacteria of the genus Clostridium (lat. Clostridium - spindle). The spores are acid-resistant, therefore they are stained red using the Aujeszky method or the Ziehl-Neelsen method, and the vegetative cell is stained blue.

Sporulation, the shape and location of spores in a cell (vegetative) are a species property of bacteria, which allows them to be distinguished from each other. The shape of the spores can be oval, spherical; location in the cell is terminal, i.e. at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in the causative agents of botulism, gas gangrene) and central in the anthrax bacillus).

Process sporulation(sporulation) goes through a series of stages, during which part of the cytoplasm and chromosome of the bacterial vegetative cell are separated, surrounded by an growing cytoplasmic membrane - a prospore is formed. The prospore is surrounded by two cytoplasmic membranes, between which a thick modified peptidoglycan layer of cortex (bark) is formed. From the inside it comes into contact with the cell wall of the spore, and from the outside - with the inner shell of the spore. The outer shell of the spore is formed by a vegetative cell. The spores of some bacteria have an additional covering - exosporium. In this way, a multilayer, poorly permeable shell is formed. Sporulation is accompanied by intensive consumption of dipicolic acid and calcium ions by the prospore, and then by the developing spore shell. The dispute acquires heat resistance, which is associated with the presence of calcium dipicolinate in it.

The spore can persist for a long time due to the presence of a multilayer shell, calcium dipicolinate, low water content and sluggish metabolic processes. In soil, for example, the pathogens of anthrax and tetanus can persist for decades.

Under favorable conditions, spores germinate, going through three successive stages: ac-

motivation, initiation, growth. In this case, one bacterium is formed from one spore. Activation is readiness for germination. At a temperature of 60-80 °C, the spore is activated for germination. Germination initiation lasts several minutes. The outgrowth stage is characterized by rapid growth, accompanied by the destruction of the shell and the emergence of a seedling.

BACTERIA(Greek bacteria rod) is a group of microscopic, mostly unicellular, organisms, diverse in biol and properties, widespread on Earth, belonging to lower forms of life.

The first information about bacteria was obtained in the 17th century from the studies of Leeuwenhoek, who discovered their basic forms. Bacteria can exist in a wide variety of conditions.

Most of them lack chlorophyll. The exceptions are anaerobic purple and green sulfur bacteria, as well as non-sulfur purple bacteria, which contain chlorophyll and use solar energy for photosynthesis. Bacteria can assimilate inorganic carbon and nitrogen, use many inorganic and organic compounds as energy sources, and carry out the transformations of carbon, nitrogen, sulfur, iron and other elements.

Along with algae, bacteria are among the most ancient organisms on Earth. The cellular structure of bacteria is similar to blue-green algae, actinomycetes (q.v.) and spirochetes (q.v.), with which the bacteria are believed to be phylogenetically related. Among the bacteria there are species that cause diseases in humans, animals and higher plants.

Taxonomy

The first attempts to classify bacteria by morphological characteristics were made in the 18th century. Later, the classification was based on physiological characteristics. The most stable ones were used as taxonomic characters - shape, color according to Tpainy (see Gram method), sporulation, type of respiration, biochemical, antigenic and other properties, but until now, no classification has been created based on the principle of phylogenetic relationship of bacteria taking into account evolutionary connections.

Bergey's classification (D. Bergey, 1957), which is based on international rules for the nomenclature of bacteria, has become widespread. The nomenclature is based on the binomial system adopted in zoological and botanical classifications (see Table 1). Various biological properties of bacteria were taken as taxonomic characteristics.

Table 1

The mycoplasmas shown in Table 1 are tiny formations, delimited instead of a rigid cell wall only by a cytoplasmic membrane, significantly different from bacteria, and are currently classified as a separate class - Mollicutes (see Mycoplasmataceae).

Morphology

There are three main forms of bacteria - spherical, rod-shaped and spiral (Fig. 1); a large group of filamentous bacteria comprises predominantly aquatic bacteria and does not contain pathogenic species.

Globular bacteria - cocci, are divided depending on the location of the cells after division into several groups: 1) diplococci (divided in the same plane and arranged in pairs); 2) streptococci (divide in the same plane, but during division they do not separate from each other and form chains); 3) tetracocci (divided in two mutually perpendicular planes, forming groups of four individuals); 4) sarcinas (divided in three mutually perpendicular planes, forming cubic groups); 5) staphylococci (divide in several planes without a specific system, forming clusters resembling bunches of grapes). The average size of cocci is 0.5-1 microns (see Cocci).

Rod-shaped bacteria have a strictly cylindrical or ovoid shape; the ends of the sticks can be smooth, rounded, or pointed. The rods can be arranged in pairs in the form of chains, but most species are arranged without a specific system. The length of the rods varies from 1 to 8 microns, the average diameter is 0.5-2 microns. It is customary to call rods that do not form spores proper bacteria (see Spores). Bacteria that form spores are called bacilli. According to the accepted nomenclature, bacilli include aerobic forms. Anaerobic spore-forming bacteria are classified as clostridia. Sporulation in bacilli and clostridia is not associated with the reproduction process. Their spores belong to the type of endospores, which are round or oval bodies that refract light and are stained using special methods (color Fig. 1 and 2). The location of spores in the cell, their size and shape are characteristic of each type of bacteria (Fig. 2). Some rods (mycobacteria, corynebacteria) form thread-like individuals, others (nodule bacteria) form branched, star-shaped forms - the so-called bacteroides (Fig. 3).

Spiral shapes of bacteria subdivided into vibrios and spirilla. The curvature of the vibrio bodies does not exceed one quarter of the spiral turn. Spirillae form bends of one or more whorls (see Vibrios, Spirillae).

Some bacteria have mobility, which is clearly visible when observed by the hanging drop method (see) or other methods. Motile bacteria actively move with the help of special organelles - flagella (see Bacterial flagella) or due to gliding movements (myxobacteria).

Capsule is present in a number of bacteria and is their external structural component (Fig. 4 and color. Fig. 3). A number of bacteria, similar to the capsule, have a formation in the form of a thin mucous layer on the surface of the cell. In some bacteria, the capsule is formed depending on the conditions of their existence. Some bacteria form capsules only in the macroorganism, others - both in the body and outside it, in particular on nutrient media containing high concentrations of carbohydrates. Some bacteria form capsules regardless of living conditions (see Capsular bacteria). The composition of the capsule of most bacteria includes polymerized polysaccharides consisting of pentoses and amino sugars, uronic acids, polypeptides and proteins. The capsule is not an amorphous formation, but is structured in a certain way. In some bacteria, for example pneumococci, the capsule determines their virulence, as well as some antigenic properties of the bacterial cell.

Cell wall bacteria determines their shape and ensures the preservation of the internal contents of the cell. Based on the characteristics of the chemical composition and structure of the cell wall, bacteria are differentiated using Gram staining.

The structure of the cell wall is different between gram-positive and gram-negative bacteria. The main layer of the cell wall, characteristic of all types of bacteria, is a rigid layer (synonym: mucopeptide layer, murein, peptidoglycan; the latter name is most consistent with the chemical structure of the layer), which contains repeating residues of amino sugars - N-acetylglucosamine and N-acetylmuramic acid, forming the basis of a linear polymer - murein.

Connected to the N-acetylmuramic acid residue is a polypeptide, which in most bacteria consists of four amino acid residues - L-alanine, D-glutamic acid, L-lysine or diaminopimelic acid (DAP) and D-alanine in a molar ratio of 1: 1: 1 : 1. Variations may be observed in the composition of the peptide depending on the type of bacteria. Lysine or DAP can be replaced by ornithine, 2,6-diaminobutary acid, etc. Sometimes an additional amino acid is attached to the glutamic acid residue. The peptide chains are connected to each other by cross-polypeptide chains, the composition of which varies widely among different bacterial species. Cross-links, for example in staphylococcus, are formed by pentaglycine bridges connecting the D-alanine of one peptide unit to the lysine of another. In some bacteria, cross-links are identical to peptide units. In E. coli, peptide chains are connected directly to each other through D-alanine on one chain and DAP on the other. A schematic representation of peptidoglycan is shown in Fig. 5.

Gram-positive bacteria, in addition to peptidoglycan, have teichoic acids (ribitol-teichoic and glycerol-teichoic), which also form a polymer and are covalently associated with peptidoglycan. Teichuronic and 2-aminomannuric acids have been found in some bacteria.

The cell walls of gram-negative bacteria, in addition to the rigid layer, include lipoprotein and lipopolysaccharide layers. The lipopolysaccharide layer (LPS) is most studied in enterobacteria, and especially salmonella. LPS is a phosphorylation complex of heteropolysaccharides covalently linked to a glucosamine-containing lipid (lipid A). The composition of L PS includes the O-antigen of the cell (in enterobacteria). The polysaccharide part of L PS consists of the main (basic) structure and the O-antigen part. The basic part, common to all enterobacteria, includes heptose, 2-keto-3-deoxyoctonate (KDO), glucose, galactose and N-acetyl-glucosamine. Through the KDO, the base part is attached to a component consisting of lipid A, ethanol amine, phosphate and KDO. On the other side (outer) side chains formed by repeating oligosaccharide units are attached to the basic structure. The outer polysaccharide chains are species-specific and are somatic O-antigens. O-specificity is determined by the carbohydrate composition of the entire side chain, the sequence of carbohydrates in it and the terminal sugar, 6-deoxy- or 3,6-dideoxyhexose. Hereditary disturbances in the biosynthesis of enterobacterial LPS basic part or O-side chains lead to the appearance of R-form mutants (see Dissociation of bacteria).

Rice. 6. Cell structure of enterobacteria (schematic representation): 1- determinant groups of O-antigen; 2 - lipoprotein layer; 3 - flagellum (H-antigen); 4 - cytoplasmic membrane; 5 and b - ribosomes in the cytoplasm; 7 - nucleoid; 8-capsule; 9 - lipopolysaccharide layer; 10 - rigid layer of the cell wall.

Lipoprotein layer(LP) in gram-negative bacteria, according to Weidel, is the outer layer of the cell wall. The LPS occupies an intermediate position; the rigid layer is the deepest located. This scheme does not explain the detection of O-antigen without preliminary destruction of the LP. Therefore, other schemes for the structure of the wall have been proposed, according to which the LP does not cover the bacterial cell with a continuous layer, but LPS passes through it in the form of “shoots,” as shown in Fig. 6. This idea was confirmed by immunochemical methods using ferritin when studying the localization of the O-antigen.

In some gram-positive bacteria, the cell wall, like in gram-negative bacteria, consists not only of a rigid layer, but has a multilayer structure. For example, in streptococci it includes a protein layer, an intermediate lipopolysaccharide layer and an internal rigid layer. The cell wall is not an enzymatically inert structure. It contains autolytic enzymes, phosphatase, and adenosine triphosphatase.

Cytoplasmic membrane bacteria is adjacent to the inner surface of the cell wall, separates it from the cytoplasm and is a very important functional component of the cell. Redox enzymes are localized in the membrane; the most important cell functions such as division, biosynthesis of a number of components, chemo- and photosynthesis, etc. are associated with the membrane system. The thickness of the membrane in most bacteria is 7-10 nm. Electron microscopy revealed that it consists of three layers: two electron-dense and an intermediate one - electron-transparent. The membrane contains proteins, phospholipids, lipoproteins, a small amount of carbohydrates and some other compounds. Many membrane proteins of B. are enzymes involved in respiration processes, as well as in the biosynthesis of components of the cell wall and capsule. The membrane also contains permeases that ensure the transfer of soluble substances into the cell. The membrane serves as an osmotic barrier, it has selective semi-permeability and is responsible for the entry of nutrients into the cell and the exit of metabolic products from it.

In addition to the cytoplasmic membrane, the bacterial cell has internal membrane system, called mesosomes, which are probably derivatives of the cytoplasmic membrane; their structure varies among different types of bacteria. Mesosomes are the most developed in gram-positive bacteria. The structure of mesosomes is heterogeneous; their polymorphism is observed even in the same species of bacteria. Internal membrane structures can be represented by simple invaginations of the cytoplasmic membrane, formations in the form of vesicles or loops (more often in gram-negative bacteria), in the form of vacuolar, lamellar, tubular formations. Mesosomes are most often localized at the cell septum (Fig. 7); their connection with the nucleoid is also noted. Since respiration and oxidative phosphorylation enzymes are found in mesosomes, many authors consider them to be analogues of mitochondria of higher cells. It is assumed that mesosomes take part in cell division, distribution of daughter chromosomes into dividing cells, and sporulation. The functions of nitrogen fixation, chemo- and photosynthesis are also associated with the cell membrane apparatus. Consequently, it can be assumed that cell membranes play a certain kind of coordinating role in the spatial organization of a number of enzyme systems and cell organelles.

Rice. 4 . Volutin grains in corynebacteria

Cytoplasm and inclusions. The internal contents of the cell consist of cytoplasm (see), which is a complex mixture of various organic compounds that are in a colloidal state. Ultrathin sections of the cytoplasm (Fig. 7) revealed a large number of grains, a significant part of which are ribosomes. The cytoplasm of bacteria may contain intracellular inclusions (color Fig. 4-6) in the form of granules of glycogen, starch, and fatty substances. In a number of bacteria, the cytoplasm contains volutin granules consisting of inorganic polyphosphates, metaphosphates and compounds close to nucleic acids. The role of volutin is not completely clear. Some authors, based on its disappearance during cell starvation, consider volutin as a reserve nutrient. Volutin has an affinity for basic dyes, exhibits chromophily and metachromasia, and is easily detected in cells in the form of large granules, especially with special staining methods.

Ribosomes bacteria are the site of cell protein synthesis, during which structures are formed consisting of a large number of ribosomes (up to 20), called polyribosomes or more often polysomes (Fig. 8). m-RNA takes part in the formation of polysomes. Upon completion of the synthesis of this protein, the polysomes again disintegrate into single ribosomes, or subunits. Ribosomes can be located freely in the cytoplasm, but a significant part of them is associated with cell membranes. In ultrathin sections of most bacteria, ribosomes are found in the cytoplasm in the form of granules with a diameter of about 20 nm. E. coli ribosomes, purified in the presence of magnesium ions, sediment during ultracentrifugation with a sedimentation rate of 70 S. At lower magnesium concentrations, they dissociate into two subunits with sedimentation constants of 50 S and 30 S. It is believed that the 50 S particle is spherical, and the 30 S - flattened shape. As the concentration of magnesium ions increases, 70 S particles form dimers. In a free state (outside protein synthesis), ribosomes are in a dissociated state in the ribosomal fraction of cells. The dissociation of ribosomes into subunits is stimulated by a special dissociation factor. 50 S and 30 S subunits have mol. weight 1.8·106 and 0.85-106, respectively. Both particles are composed of ribosomal RNA (or rRNA) and protein. The 50 S particle contains one molecule of 23 S and 5 S rRNA. The 30 S particle contains one molecule of 16 S rRNA. The protein composition of ribosomes is heterogeneous. 30 S particles consist of twenty-one, and 50 S particles consist of thirty to thirty-five different proteins. Some of the proteins of the 30 S ribosomal particles are needed both for the assembly of ribosomes and for their functioning, the other part is important only in a functional sense. Ribosomal RNA is essential for the proper assembly and organization of ribosomes.

The degree of ribosome aggregation is regulated by magnesium ions. Polyamines and ribonuclease I, which is believed to be involved in the hydrolysis of m-RNA, are found in ribosomes.

Rice. 10. Autoradiography of the chromosome of the coli bacterium. A circularly closed structure is visible; top left - replication diagram: X - starting point of replication, Y - growth point; A - replicated area; B - unreplicated area; B - replication point.

Core. Bacteria have a discrete nuclear structure, which, due to the unique structure, is called a nucleid (Fig. 9). B.'s nucleoids contain the bulk of the cell's DNA. They are stained by the Feilgen method (see Deoxyribonucleic acids), are clearly visible when stained according to Romanovsky-Giemsa (see Romanovsky-Giemsa method), after acid hydrolysis or in a living state with phase-contrast microscopy, as well as on ultrathin sections in an electron microscope ( Fig. 7 and 9). The nucleoid is defined as a compact single or double formation. In growing crops, nucleoids often appear as bifurcated structures, reflecting their division. Mitotic division of nuclear structures was not detected in bacteria. The shape of nucleoids and their distribution in the cell are very variable and depend on a number of reasons, including the age of the culture. In electron micrographs, light areas of lower optical density are visible at the locations of nucleoids. The nuclear vacuole is not separated from the cytoplasm by the nuclear envelope. The shape of the vacuole is not constant. The nuclear areas are filled with bundles of thin filaments forming a complex weave. No histones were found in the nuclear structures of bacteria (see); It is assumed that their role in bacteria is performed by polyamines. The nuclei of bacteria are not like the nuclei of other organisms. This served as the basis for distinguishing bacteria into the group of prokaryotes, in contrast to eukaryotes, which have a nucleus containing chromosomes, a membrane, and dividing by mitosis. The bacterial nucleoid is connected to the mesosome. The nature of the connection is not yet known. The bacterial chromosome has a circularly closed structure. This was shown by autoradiography in E. coli (Fig. 10), previously labeled with 3H-thymidine. The DNA structure was judged from the distribution of labeled thymidine grains. It is estimated that the length of the DNA cell closed in a ring is 1100-1400 µm, and the molecular weight is 2.8 × 109 [J. Cairns, 1963].

Flagella and villi. On the surface of some bacteria there are organelles of movement - flagella (Fig. 11). They can be detected using special staining techniques, dark-field microscopy, or an electron microscope. Flagella have a spiral shape, and the pitch of the spiral is specific to each type of bacteria. Based on the number of flagella and their location on the cell surface, the following groups of motile microbes are distinguished: monotrichs, amphitrichs, lophotrichs and peritrichs. Monotrichs have one flagellum located at one of the poles of the cell and, less often, subpolarly or laterally. In amphitrichs, there is one flagellum at each pole of the cell. Lophotrichs have a bundle of flagella at one or two cell poles. In peritrichs, flagella are distributed in no particular order throughout the cell body.

M.A. Peshkov (1966) offers slightly different terminology. He combines amphi- and lophotrichs with the term “multrichs” and distinguishes a mixed type, having two or more flagella of different types at different points of attachment. The base of the flagella (blepharoplast) is located in the cytoplasmic membrane. Flagella consist almost entirely of the protein flagellin.

On the surface of some bacteria (enterobacteria), in addition to flagella, there are villi (fimbriae, pili), visible only under an electron microscope (Fig. 12). There are several morphological types of villi. The first type (general) and villi, which exist only in the presence of sex factors in the cell, have been most fully studied (see Sex factor of bacteria). General type villi cover the entire surface of the cell and consist of protein; There are 1-4 sexual villi per cell. Both have antigenic activity (see Conjugation in bacteria).

Physiology

By chemical composition Bacteria are no different from other organisms.

Bacteria contain carbon, nitrogen, hydrogen, oxygen, phosphorus, sulfur, calcium, potassium, magnesium, sodium, chlorine and iron. Their content depends on the type of bacterium and cultivation conditions. An obligatory chemical component of bacterial cells, like other organisms, is water, which is a universal dispersion medium of living matter. The bulk of the water is in a free state; its content varies among different bacteria and accounts for 70-85% of the wet weight of bacteria. In addition to free water, there is an ionic fraction of water and water associated with colloidal substances. In terms of the composition of organic components, bacterial cells are similar to the cells of other organisms, differing, however, in the presence of some compounds. The composition of bacteria includes proteins, nucleic acids, fats, mono-, di- and polysaccharides, amino sugars, etc. Bacteria have unusual amino acids: diaminopimelic (also found in blue-green algae and rickettsia); N-methyllysine, which is part of the flagellin of some bacteria; D-isomers of some amino acids. The content of nucleic acids depends on cultivation conditions, growth phases, and the physiological and functional state of cells. The DNA content in a cell is more constant than RNA. The nucleotide composition of DNA is unchanged during bacterial development, is species-specific, and is used as one of the most important taxonomic characteristics. Bacterial lipids are diverse. Among them are fatty acids, phospholipids, waxes, and steroids. Some bacteria form pigments (color Fig. 7-9) with an intensity that varies widely within the same species and depends on growing conditions. Solid nutrient media are more favorable for the formation of pigments. Based on their chemical structure, carotenoid, quinone, melanin and other pigments are distinguished, which can be red, orange, yellow, brown, black, blue or green. More often, pigments are insoluble in nutrient media and stain only cells. Water-soluble pigments (pyocyanin) diffuse into the medium, coloring it. Bacterial pigments also include bacteriochlorophyll, which gives purple or green color to some photosynthetic bacteria.

Enzymes bacteria are divided into those that function only inside the cell (endoenzymes) and only outside the cell (exoenzymes). Endoenzymes mainly catalyze synthetic processes, respiration, etc. Exoenzymes catalyze mainly the hydrolysis of high molecular weight substrates to compounds with a lower molecular weight that can penetrate into the cell.

In the cell, enzymes are associated with corresponding structures and organelles. For example, autolytic enzymes are associated with the cell wall, redox enzymes are associated with the cytoplasmic membrane, enzymes associated with DNA replication are associated with the membrane or nucleoid.

The activity of enzymes depends on a number of conditions, primarily on the temperature of growing bacteria and the pH of the environment. Lowering the temperature reversibly reduces, and raising it to certain limits (40-42°) increases the activity of enzymes. In thermophilic and psychrophilic bacteria, the optimum enzyme activity coincides with the optimal growth temperature. The optimal temperature for mesophilic bacteria, which includes pathogenic bacteria, is approximately 37°. The optimum pH generally lies in the range of 4-7. Variations in pH optimum occur. Bacterial enzymes whose activity does not depend on the presence of a substrate in the culture medium are called constitutive. Enzymes, the synthesis of which depends on the presence of a substrate in the medium, are called inducible (the old name is adaptive). For example, the formation of β-galactosidase in Escherichia coli begins only when lactose is added to the medium, which induces the synthesis of this enzyme.

Enzyme synthesis is controlled by inhibition by the end product or by induction and repression.

The enzymatic activity of bacteria is used for their identification, most often the saccharolytic and proteolytic properties are studied. Some enzymes produced by pathogenic bacteria are virulence factors (see).

Nutrition. Bacteria use nutrients only in the form of relatively small molecules that penetrate the cell. This method of nutrition, characteristic of all organisms of plant origin, is called holophytic. Complex organic substances (protein, polysaccharides, fiber, etc.) can serve as a source of nutrition and energy only after their preliminary hydrolysis to simpler compounds soluble in water or lipoids. The ability of various compounds to penetrate the cytoplasm of cells depends on the permeability of the cytoplasmic membrane and the chemical structure of the nutrient.

The substances that serve as a source of nutrition for bacteria are amazingly diverse. The most important element necessary for living organisms is carbon. Some types of bacteria (autotrophs) can use inorganic carbon from carbon dioxide and its salts (see Autotrophic organisms), others (heterotrophs) - only from organic compounds (see Heterotrophic organisms). The vast majority of bacteria are heterotrophs. Carbon assimilation requires an external source of energy. A few species of bacteria that have photosynthetic pigments use the energy of sunlight. These bacteria are called photosynthetic bacteria. Among them there are autotrophs (green and purple sulfur bacteria) and heterotrophs (non-sulfur purple bacteria). They are also called photolithotrophs and photoorganotrophs, respectively. Most bacteria use the energy of chemical reactions and are called chemosynthetic. Chemosynthesizing autotrophs are called chemolithotrophs, and heterotrophs are called chemoorganotrophs.

Heterotrophic bacteria absorb carbon from organic compounds of various chemical natures. Substances containing unsaturated bonds or carbon atoms with partially oxidized valences are easily digestible. In this regard, the most accessible sources of carbon are sugars, polyhydric alcohols, etc. Some heterotrophs, along with the assimilation of organic carbon, can also assimilate inorganic carbon.

Attitudes towards nitrogen sources also vary. There are bacteria that assimilate mineral and even atmospheric nitrogen. Other bacteria are unable to synthesize protein molecules or some amino acids from the simplest nitrogen compounds. In this group there are forms that use nitrogen from individual amino acids, from peptones, complex protein substances and from mineral sources of nitrogen with the addition of amino acids that are not synthesized by them. Many pathogenic bacteria belong to this group.

Breath. Some of the substances that penetrate into the bacterial cell, oxidizing, supply it with the necessary energy. This process is called biol, oxidation or respiration.

Biological oxidation comes down mainly to two processes: dehydrogenation of the substrate with subsequent transfer of electrons to the final acceptor and accumulation of the released energy in a biologically accessible form. Oxygen and some organic and inorganic compounds can serve as the final electron acceptor. In aerobic respiration, the final electron acceptor is oxygen. Energy processes in which the final electron acceptor is not oxygen, but other compounds are called anaerobic respiration, and some researchers include as anaerobic respiration proper those processes in which the final electron acceptor is inorganic compounds (nitrates and sulfates).

Fermentation refers to energy processes in which organic compounds act simultaneously as electron donors and acceptors.

Among the bacteria there are strict aerobes (see), developing only in the presence of oxygen, obligate anaerobes, developing only in the absence of oxygen, and facultative anaerobes (see), capable of development in both aerobic and anaerobic conditions. Most bacteria have a spatially organized system of respiratory enzymes, called the respiratory chain or electron transport chain.

Respiration in bacteria, like the respiration of other organisms, is associated with processes of oxidative phosphorylation and is accompanied by the formation of compounds rich in high-energy bonds (ATP). The energy stored in these compounds is used as needed.

Bacteria can use a variety of organic compounds (carbohydrates, nitrogen-containing substances, fats and fatty acids, organic acids, etc.) as an energy source. The ability to obtain energy as a result of the oxidation of inorganic compounds is inherent in only a small group of bacteria. The inorganic substances they oxidize are specific to each type of bacteria. These bacteria include nitrifying bacteria, sulfur bacteria, iron bacteria, etc. Among them are aerobes and anaerobes.

Photosynthetic bacteria convert visible light energy directly into ATP; This process, carried out during photosynthesis, is called photophosphorylation.

Growth and reproduction

A bacterial cell begins to divide after the completion of successive reactions associated with the reproduction of its components.

The most important process of cell growth is the reproduction of its hereditary apparatus. The division of the nucleoid is preceded by the processes of DNA replication (see Replication). Replication begins when the cell's DNA/protein ratio reaches a certain level. Initiation of replication requires the synthesis of specific protein products. On the replicating DNA of a cell, when studied using the autoradiographic method, two points are distinguished: the point of origin of replication and the point of growth (Fig. 10). The replicative point moves along the entire DNA of the cell, which, as noted, has a circularly closed structure. The time it takes for the replication point to pass from the beginning to the end of the entire circular DNA structure, or the time of DNA synthesis, is constant and does not depend on the rate of cell growth. In rapidly growing cultures, when the generation time (the time between cell divisions) is less than the time required for DNA replication (40-47 minutes in E. coli B/r), a new initiation begins before the previous one ends. Thus, rapidly growing crops have several replication points (forks). The process of DNA replication is accompanied by the segregation of synthesized DNA chains into newly formed daughter cells. Cell mesosomes play an important role in separating DNA strands.

The growth of rod-shaped cells during the generation cycle is reduced to an exponential increase in their length. During division, cell growth slows down and begins again after division.

The end of DNA replication is the point that initiates cell division. Inhibition of DNA synthesis before the end of replication leads to disruption of the division process: the cell stops dividing and grows in length. Using the example of E. coli, it is shown that the onset of division requires the presence of a thermolabile protein and a ratio between individual polyamines in the cell in which the amount of putrescine must exceed the amount of spermidine. There is evidence of the importance of phospholipids and autolysins for the process of cell division.

A growing bacterial culture synthesizes a complete set of ribosomes. Ribosomal RNA is initially synthesized on a DNA template, then modified and converted into mature 16 S and 23 S rRNA. 5 S rRNA is also not a direct product of transcription (see). Ribosome precursors do not contain the full complement of ribosomal proteins. The full set appears only during the maturation process.

The mechanism of reproduction of mesosomes, as well as the membrane apparatus of the cell, is not yet clear. It is assumed that as a bacterial cell grows, the mesosomes gradually separate.

As a bacterial cell grows, a cell septum forms next to the mesosome (Fig. 7). The formation of a septum leads to cell division. The newly formed daughter cells separate from each other. In some bacteria, the formation of a septum does not lead to cell division: multilocular cells are formed.

A number of mutants have been obtained in E. coli, in which a cell septum is formed either in an unusual location, or, along with a septum with a usual localization, an additional septum is formed close to the cell pole. As a result of the division of such mutants, both ordinary cells and small cells (mini-cells) measuring 0.3-0.5 microns are formed. Mini-cells, as a rule, are deprived of DNA, since when the parent cell divides, the nucleoid does not enter them. Due to the absence of DNA, minicells are used in bacterial genetics to study the expression of gene function in extrachromosomal factors of heredity and other issues.

When grown in liquid nutrient media, the growth rate of the cell population changes over time. The growth of a bacterial population is divided into several phases. After the cells are inoculated into a fresh nutrient medium, the bacteria do not multiply for some time - this phase is called the initial stationary or lag phase. The lag phase turns into a phase of positive acceleration. In this phase, bacterial division begins. When the cell growth rate of the entire population reaches a constant value, the logarithmic phase of reproduction begins. During this period, it is possible to calculate the generation time, the number of generations and some other indicators. The logarithmic phase is replaced by a phase of negative acceleration, then the stationary phase begins. The number of viable cells in this phase is constant (M-concentration is the maximum concentration of viable cells). This is followed by a phase of population decline. The rate of population growth is influenced by: the type of bacterial culture, the age of the sown culture, the composition of the nutrient medium, growing temperature, aeration, etc.

During the growth of a cell population, metabolic products accumulate in them, nutrients are depleted, and other processes lead to the transition to stationary and subsequent phases. With the constant addition of nutrients and the simultaneous removal of metabolic products, it is possible to achieve a long stay of population cells in the logarithmic phase. Most often, a chemostat is used for this purpose (see).

Despite the constant growth rate of the bacterial population in the logarithmic phase, individual cells are still in different stages of division. Sometimes it is important to synchronize the growth of all cells in a population, that is, to obtain a synchronous culture. Simple methods of synchronization are changing temperature conditions or cultivating under nutrient-poor conditions. First, the culture is placed in non-optimal conditions, then they are replaced by optimal ones. In this case, the division cycle of all cells in the population is synchronized, but synchronous cell division usually occurs no more than 3-4 cycles.

Previously, hypotheses have been repeatedly put forward according to which the transformation of one form of bacteria into another in the development cycle occurs in a vicious circle. All these hypotheses are united by the general term “cyclogeny”. Theoretical ideas about cyclogeny are currently of only historical interest. However, actual data on the processes of dissociation of bacteria (see) have not lost their significance.

Action of external factors

The viability of bacteria under the influence of external factors is studied by different methods, for example, by counting surviving cells. To do this, survival curves are constructed that express the dependence of the number of surviving cells on the exposure time.

Bacteria are relatively resistant to low temperatures. Bacteria are more sensitive to high temperatures. Usually, when bacteria are heated at a temperature of 60-70°, the death of vegetative cells occurs, but the spores do not die. The sensitivity of bacteria to high temperatures is used during sterilization (see).

Different types of bacteria react differently to drying. Some bacteria (for example, gonococci) die very quickly, while others (mycobacteria) are very resistant. However, by observing certain conditions (presence of vacuum, special media), it is possible to obtain dried lyophilized bacterial cultures that remain viable for a long time (see Lyophilization).

Bacteria can be destroyed by mechanical rubbing with various powders (glass, quartz), as well as by exposure to ultrasound.

Bacteria are sensitive to ultraviolet rays; The most effective rays are those with a wavelength of about 260 nm, which corresponds to their maximum absorption by nucleic acids. Ultraviolet rays have a mutagenic effect. X-rays also have lethal and mutagenic effects (see Mutagens).

Sensitivity to chemotherapeutic drugs and antibiotics depends on the type of bacteria and the mechanism of action of the drug on the cell. Resistant forms can be obtained from sensitive bacteria as a result of mutation or through the transfer of factors of multidrug resistance of microorganisms (see).

Distribution of bacteria in nature and their role in the cycle of substances

Pathogenicity and virulence. Bacteria live in soil, water, human and animal bodies. Diverse groups of bacteria can develop in conditions that are inaccessible to other organisms. The qualitative and quantitative composition of bacteria living in the external environment depends on many conditions: pH of the environment, temperature, availability of nutrients, humidity, aeration, the presence of other microorganisms (see Antagonism of microbes), etc. The more diverse organic compounds the environment contains, the more bacteria can be found in it. In uncontaminated soils and waters, a relatively small number of saprophytic forms of bacteria are found. The soil is inhabited by spore-forming and non-spore-forming bacteria, mycobacteria, myxobacteria, and coccal forms. In water there are a variety of spore-forming and non-spore-forming bacteria and specific aquatic bacteria - aquatic vibrios, filamentous bacteria, etc. Various anaerobic bacteria live in the sludge at the bottom of reservoirs. Among the bacteria that live in water and soil, there are nitrogen-fixing, nitrifying, denitrifying, and cellulose-splitting bacteria. etc. The seas and oceans are inhabited by bacteria that grow at high concentrations of salts and high pressure, and luminous species are found. In polluted waters and soil, in addition to soil and aquatic saprophytes, there are large numbers of bacteria that live in the body of humans and animals - enterobacteria, clostridia, etc.

An indicator of fecal contamination is usually the presence of E. coli. Due to the wide distribution of bacteria and the unique metabolic activity of many of their species, they are of exceptionally great importance in the cycle of substances in nature. Many types of bacteria participate in the nitrogen cycle - from species that break down protein products of plant and animal origin, to species that form nitrates, which are absorbed by higher plants. The metabolic activity of bacteria determines the mineralization of organic carbon and the formation of carbon dioxide, the return of which to the atmosphere is important for maintaining life on Earth. The absorption of carbon dioxide from the atmosphere is carried out by green plants due to their photosynthetic activity. Bacteria play a major role in the cycle of sulfur, phosphorus, and iron.

A relatively small proportion of all known microbes are capable of causing diseases in humans and animals. The potential ability of bacteria to cause infectious diseases, which is their species characteristic, is called pathogenicity or pathogenicity. In the same species, the severity of pathogenic properties can vary quite widely. The degree of pathogenicity of a strain of a certain type of bacteria is called its virulence (see). Among bacteria there are conditionally pathogenic species, the pathogenicity of which depends on the state of the macroorganism, the external environment, etc.

Genetics of bacteria

Bacterial genetics is a branch of general genetics that studies heredity and variability in bacteria. The relative simplicity of the organization of bacteria, their ability to grow in synthetic media, and rapid reproduction make it possible to analyze relatively rare changes in the genome (see) of bacteria that make up multibillion-dollar populations and to monitor their inheritance. For this purpose, special methods are used to ensure selection from a huge population of individual genetically modified bacterial cells, transfer of a chromosome or its fragments from one cell (donor) to another (recipient), followed by genetic analysis of the resulting recombinants (see Recombination). Methods of genetic analysis (see) of bacteria have made it possible to study not only the organization of the bacterial chromosome, but also to decipher the fine structure of the gene, as well as to establish the functional relationships of the genetic units that make up individual bacterial operons (see).

The development of bacterial genetics is associated with the study of bacterial transformation (see), which made it possible to establish the role of DNA as the material basis of heredity. When studying genetic transformation in bacteria, methods for extracting and purifying DNA, biochemical and biophysical methods for analyzing its properties were developed. This made it possible not only to study genetic changes at the cellular level, but also to compare these changes with changes in DNA structure. Thus, in combination with genetic methods, methods of biochemical research of genetic material have provided the opportunity to analyze the patterns of bacterial genetics at the molecular level.

Among bacteria, the most studied genetically are Escherichia coli, in which methods of transferring genetic material (chromosomes or its fragments) from a donor to a recipient, carried out either by direct crossing (see Conjugation in bacteria) or with the help of bacterial viruses (see. Transduction). Other microorganisms that have the same types of exchange of genetic material and are similar in genetic characteristics to E. coli are Salmonella.

The patterns of genetic exchange established for E. coli and Salmonella are also inherent in a number of other microorganisms that play an important role in infectious pathology. The phenomena of conjugation and transduction have also been found in Shigella and some other pathogenic microorganisms, which allows for genetic analysis of the factors determining their pathogenicity.

To elucidate the molecular mechanisms and various genetic phenomena, microorganisms capable of genetic transformation, in which recipient bacteria absorb purified DNA extracted from donor bacteria, are of significant interest. Transformation experiments reveal the genetic activity of isolated, extracellular DNA, which makes it possible to analyze the functional activity of DNA subjected to various influences that change its structure both in vivo and in vitro.

Therefore, transformable bacterial species such as Bac are widely used in molecular genetic studies. subtilis, H. influenzae, Pneumococcus, etc.

The properties of bacteria, like any other organisms, are determined by a set of genes inherent in them. The recording of genetic information encoded in bacterial genes is carried out on the basis of a universal triplet code (see Genetic code). Yanovsky (S. Janofsky) obtained evidence of colinearity (correspondence) between the nucleotide sequence and the amino acid sequence in a polypeptide and established the in vivo composition of individual triplets encoding the inclusion of various amino acids.

The set of genes inherent in bacteria determines their genotype (see). Bacteria with the same genotype are not always identical in their properties; their properties can vary depending on the cultivation environment, the age of the bacterial cultures, the growing temperature and a number of other environmental factors. The genotype determines only the properties potentially inherent in bacterial cells, the expression of which depends on the functioning (activity) of specific genetic structures. The bacterial chromosome includes 2 types of functionally different genetic structures: structural genes, which determine the specificity of the proteins that a given cell is capable of synthesizing, and regulatory genes, which regulate the activity of structural genes depending on environmental conditions, in particular on the presence or absence of the substrate of the synthesized enzyme or on the concentration of the required cell connection, on the state of the genetic material (DNA replication), etc.

In the active state, structural genes are transcribed (see Transcription), that is, they become available for reading genetic information using DNA-dependent RNA polymerase. Messenger RNA (i-RNA) formed during transcription is translated into the corresponding polypeptide, the structure of which is encoded in these structural genes.

Based on the type of regulation, bacterial synthetic systems are divided into 2 types: catabolic and anabolic. The former utilize the energy needed by the cell, the latter ensure the biosynthesis of compounds needed by bacteria.

The catabolic system of E. coli, which breaks down lactose into glucose and galactose, was studied in detail by Jacob and Monod (F. Jacob, J. Monod).

The enzymes of this system (β-galactosidase, galactoside permease and galactoside transacetylase) are determined by the corresponding structural genes. Next to the structural genes there is a regulatory site, the so-called operator, that “turns on” and “turns off” the reading of information (transcription) from structural genes.

Another regulatory unit of this system is a gene that controls the synthesis of a repressor - a protein capable of connecting to an operator. In the presence of a repressor, structural genes are not transcribed by RNA polymerase and the synthesis of the corresponding enzymes does not occur. Between the operator and the regulator gene there is a short section of DNA - the promoter - the landing site for RNA polymerase. Lactose added to the bacterial cultivation medium binds the repressor, the operator becomes free, and structural genes begin to be transcribed, resulting in the synthesis of enzymes. Thus, lactose, which is a substrate for the action of enzymes, acts as an inducer of their synthesis.

This kind of regulation is also characteristic of other catabolic systems. The synthesis of enzymes induced by the substrates of their action is called inducible.

A different kind of regulation is inherent in anabolic bacterial systems. In these systems, the gene regulator controls the synthesis of an inactive repressor-aporepressor. With small amounts of the final metabolite controlled by the structural genes of a given biochemical pathway (for example, some amino acid), the aporepressor does not bind to the operator gene and, therefore, does not interfere with the work of the structural genes and the synthesis of this amino acid. In the case of excessive formation of the final product, the latter begins to function as a corepressor. By binding to an aporepressor, the corepressor converts it into an active repressor that binds to the operator gene. As a result, the transcription of structural genes and the synthesis of corresponding compounds stop, that is, repression of the system is observed. As the cell consumes the excess final metabolite, the active repressor again turns into an aporepressor, the operator gene is released and the structural genes become active again, that is, derepression of the system occurs.

Thus, genetic systems of both types - catabolic (inducible) and anabolic (repressible) - are characterized by feedback-type regulation: the accumulation and consumption of the final product regulates its synthesis by anabolic systems; in catabolic systems, the substrate of the action of synthesized enzymes acts as a regulator.

Shifts in the course of cellular synthetic processes, as a result of which non-heritable changes in the properties of bacteria of the same genotype can occur, can be expressed to varying degrees depending on environmental conditions. Sharply disrupted living conditions can lead to the shutdown of the function of individual structural genes or their hyperfunction, which in turn can lead to significant morphological changes, unbalanced growth and, ultimately, cell death.

The set of properties of bacteria revealed in given conditions of existence is called a phenotype. The phenotype of bacteria, although dependent on the environment, is controlled by the genotype, since the nature and degree of phenotypic changes possible for a given cell is determined by a set of genes, that is, the genotype.

Both structural and regulatory genes of bacteria are localized in the bacterial chromosome and together form the genetic apparatus of bacteria. In addition, bacteria can carry extrachromosomal genetic determinants - plasmids (see), which, as a rule, are not vital for the cell. On the contrary, activation of the functions of some of them (for example, bacteriocins) is detrimental to bacterial cells that do not carry plasmids. At the same time, plasmid elements impart a number of properties to bacteria that are of great interest from the point of view of infectious pathology. Thus, plasmid determinants may be responsible for multiple drug resistance (see R-factor), the production of alpha-hemolysin and other bacterial toxins.

The chromosome of bacteria, like the cells of higher organisms, is localized in the nucleus.

Unlike the cells of higher organisms, the bacterial nucleus lacks a shell and is called a nucleoid. The number of nucleoids in bacterial cells varies depending on the growth phase of the culture: the number of nucleoids in E. coli is maximum in rapidly multiplying cultures that are in the logarithmic growth phase. In the stationary growth phase, E. coli contain one nucleoid. The bacterial chromosome is a DNA molecule closed in a ring with a molecular weight of the order of 1.5 - 2 X 109 daltons.

Rice. 13. Diagram of the sequence of transfer of genetic material during E. coli conjugation, illustrating the ring structure of the bacterial chromosome. The letters represent different genes. Right arrow - sequence of gene transfer (C, D, E, E, A, B) to the recipient by donor strain 1; left arrow - sequence of gene transfer (D, D, C, B, A, E) to the recipient by donor strain 2.

The ring structure of the bacterial chromosome was established by three methods: autoradiographic, electron microscopic and genetic. In the first case, autoradiograms of circular structures of bacterial DNA were obtained, in the second, electron microscopic images of isolated circular DNA were obtained, in the third, patterns of genetic exchange were established that can only be explained by the circular structure of the chromosome. This can be illustrated with the following hypothetical example. Let us assume that in the process of crossing bacteria (conjugation), genes designated by the letters A, B, C, D, D, E are transferred from one bacterium to another. One of the donor strains used is Hfr (an abbreviation for the English expression high frequency of recombination - high frequency recombination) has a starting point for chromosome transfer in the region of gene B. In this case, the following order of gene transfer is observed: B, D, D, E, A, B. The second strain Hfr begins chromosome transfer from gene D and transfers it in the direction opposite to the previous one . In this case, genes are transmitted in the following order: D, D, C, B, A, E. The experimentally demonstrated preservation of the sequence of gene transmission when the order of their transfer is changed is easily explained by the ring structure of the chromosome (Fig. 13).

Methods that make it possible to experimentally carry out the transfer of genetic material in bacteria (conjugation, transduction and transformation) have made it possible to construct a genetic map of the bacterial chromosome, reflecting the relative localization of genes. For the purpose of genetic mapping, conjugation is widely used, in which large sections of the bacterial chromosome, and sometimes the entire donor chromosome, are transferred to the recipient. When conjugation mapping, various approaches are used: they establish the transmission of individual genes over time, identify linked gene transmission, establish the frequency of transmission of genes that are not subject to selection (non-selective), located proximally and distally relative to the selected gene, etc. Conjugation, however, in the majority cases does not provide the possibility of sufficiently accurate mapping, since in this case recombination (see) is carried out on relatively extended sections of the chromosome. Precise mapping is carried out using transduction, in which shorter fragments of the bacterial chromosome are transferred, not exceeding 0.01 of its length. One of the main methods of transduction mapping is to determine the possibility of cotransduction (that is, joint transmission) of the mapped gene and a gene whose localization on the chromosome is known. The presence of cotransduction indicates the close (linked) location of the analyzed genes. Transduction can also be used to determine the order of genes. For this purpose, a special method of genetic analysis is used - the so-called three-point test, in which the analysis of crosses is carried out regarding three genes.

Transformation for mapping is used relatively rarely. Treatment of recipient bacteria with transforming DNA makes it possible to transfer only very small sections of the bacterial chromosome. As a result, only genes that constitute linkage groups can be analyzed using transformation.

The genetic map of E. coli K-12, built on the basis of many years of genetic research conducted in various laboratories around the world, currently includes several hundred localized genes.

Rice. 14. Circular genetic map showing the location of genes on the E. coli chromosome. Genes are indicated by symbols deciphered in the table. 3. The numbers on the inner surfaces of the circles indicate the units of map length (the time during which a given gene is transmitted during conjugation), expressed in minutes (from 0 to 90 minutes).

In Fig. Figure 14 shows the genetic map of E. coli, published in 1970 by A. L. Taylor in the journal Bacteriological Reviews (USA). For ease of orientation, the circle of the genetic map, which schematically depicts a chromosome, is divided into segments - minutes, which in total constitute the time required for the transfer of the entire chromosome during the conjugation process. For E. coli this time is about 90 minutes. Symbols placed around a circle indicate the corresponding genes and are deciphered in Table 3, which includes about 2000 bacterial genes, the functions of which in the life of a bacterial cell have been largely studied. Information about the localization of genes on the bacterial chromosome makes it possible to solve specific problems in practical microbiology. They serve as a necessary prerequisite for studying the virulence and pathogenicity of bacteria, their resistance to drugs, the possibility of creating attenuated strains, and for other purposes. There is a pronounced homology in the arrangement of the genes of Escherichia coli and Salmonella.

In some cases, genes (cistrons) that control individual stages of the synthesis of the final metabolite are located in one section of the bacterial chromosome. The sequence of gene location corresponds to the sequence of use of the intermediate compounds determined by them during the synthesis of the final metabolite. In the same region of the chromosome where the structural genes are located, regulatory genetic units may also be located, which together with the corresponding structural genes constitute an operon (see). An example of such operons are groups of genes that provide the synthesis of histidine, tryptophan, etc.

In other cases, structural and regulatory genes of the same biochemical pathway are located in different regions of the bacterial chromosome, as exemplified by genes that control methionine synthesis, arabinose cleavage, purine synthesis, etc.

The study of genetic exchange in bacteria is not limited to the purpose of genetic mapping. The possibility of such an exchange is also used to obtain new strains of bacteria useful for humans. In particular, recombination between pathogenic and non-pathogenic bacteria can be used to construct attenuated strains, that is, strains with weakened virulence, suitable for the production of live vaccines. Such strains can be obtained from pathogenic bacteria (for example, from dysentery bacteria) by replacing the genetic region (or regions) that determines their pathogenicity with the corresponding regions of the chromosome of non-pathogenic bacteria (for example, Escherichia coli). To create attenuated strains, it is necessary not only to ensure the possibility of genetic exchange, but also to first study the genetic basis of pathogenicity, virulence, immunogenicity and map the genes that determine them. Only under this condition can the construction of full-fledged vaccine strains be carried out, having lost only virulence, but retaining the properties that ensure immunogenicity.

Genetic exchange in bacteria also occurs in their natural habitat, resulting in recombination variability of bacteria, manifested in the formation of atypical forms. This circumstance gives practical interest to the study of the recombination process, since the mechanism of formation, pathogenetic and diagnostic significance of atypical forms are the most pressing issues of infectious pathology.

In addition to phenotypic and recombination variability, bacteria are characterized by mutational variability, that is, variability caused by mutations, which are structural rearrangements of genes, their complete or partial loss (deletions), not associated with recombinations. Bacteria are widely used to study the patterns of the mutation process. Mutation (see), that is, a change in genotype, is a phenomenon caused by the action of mutagenic agents. They are the basis for all genetic research, since the study of gene function, their mapping and other genetic problems can only be solved with the help of appropriate mutants. The nature of bacterial mutants formed under the influence of mutagenic agents does not depend on the mechanism of action of mutagens (see). The idea that was created at the first stage of the development of bacterial genetics about the adequacy of the mutational variability of bacteria to the mutagens used, that is, about the specific action of the latter, turned out to be erroneous, just as the concept of the spontaneous nature of the mutation process turned out to be erroneous. This idea was based on the fact that when exposed to agents that caused the death of the main part of the bacterial population, researchers obtained mutations corresponding to the agent used. For example, the action of sulfonamides was accompanied by the release of sulfonamide-resistant mutants, the action of phages was accompanied by the release of phage-resistant mutants, etc. The works of S. Luria, M. Delbruck, J. Lederberg and H. Newcombe it was shown that the formation of such mutants occurs before the addition of a destructive agent, and the latter only plays the role of a selection factor. Mutational changes in bacterial populations occur in many genes, but breeding agents select only the relevant mutations. For example, a mutating population of bacteria may contain mutants of various kinds: auxotrophs - unable to synthesize any compounds necessary for the cell; mutants that have lost or acquired the ability to ferment individual carbohydrates; resistant to antibiotics, etc. When such a population is sown on a medium with an antibiotic, non-mutated individuals, as well as individuals carrying mutations that are not related to antibiotic resistance, will not grow. Only bacteria that have mutations in the gene that determines the corresponding resistance will grow on such a medium. This, however, does not mean that the origin of antibiotic-resistant mutants is associated with exposure to the selection agent. The cause of the emergence of resistant mutants, as well as mutants that remained undetected on a medium with an antibiotic, are mutational events that occurred before exposure to the selection agent. In turn, this does not mean that a selection agent cannot have mutagenic activity, but if it has such activity, it induces mutations not only in genes corresponding to its mechanism of action, but also, like any other mutagen, in a wide variety of genes, and selects only accordingly modified bacteria.

The inconsistency of the concept of spontaneous mutation of bacteria was refuted on the basis that when testing numerous chemical compounds and physical agents, possibly acting on commonly cultivated populations of bacteria, it was found that mutagenic activity is characteristic of an extremely wide range of factors, including natural metabolites of bacteria. The action of these factors is not always controllable, but explains the reason for the occurrence of so-called spontaneous mutations.

According to the modern concept, spontaneous mutations are a phenomenon of the same order as experimentally obtained mutations, called induced. Both those and others are causally determined. The only differences are that induced mutations arise under the influence of specially used mutagenic agents, while the agents causing spontaneous mutations remain unclear. The term “spontaneous”, therefore, does not reflect the essence of the phenomenon and is used conventionally to designate mutations that occur without special influences.

Mutations caused by the influence of mutagenic agents arise as a result of changes in the sequence of DNA nucleotides, the manifestation of which is the loss or change in the function of the polypeptide encoded by a given gene, or a change in the properties of regulatory units of the bacterial genome (operator, promoter). According to the “extent”, gene and chromosomal mutations are distinguished. The former affect one gene, the latter extend to more than one gene. Chromosomal mutations occur as a result of the loss of a large number of nucleotides (deletions). Gene mutations are often point mutations, that is, they involve the replacement, insertion, or deletion of one pair of DNA nucleotides. There are simple and complex substitutions of nitrogenous bases in DNA - transitions and transversions (see Mutation).

Bacteria are characterized by direct and reverse mutations. The latter often have a suppressor character. All known mutagens have mutagenic effects on bacterial cells. The most commonly used mutagens in bacteriological genetic research are ultraviolet rays, penetrating radiation, mono- and bifunctional alkylating agents, base analogues, and a number of others.

Recent studies carried out on bacteria have revealed the presence of genetically determined systems that ensure the repair of damage to genetic material (DNA). These studies launched a new direction in genetics and molecular biology. Data obtained from the study of bacterial reparative activity led to a revision of a number of ideas about the mechanisms of action of mutagenic agents, the formation, fixation and phenotypic expression of mutational changes.

Antigens of bacteria

Bacterial antigens are localized in flagella, capsule, cell wall, membranes and other cell structures. Bacterial antigens are biologically active components of the cell that determine its immunogenic, toxic and invasive properties. Deciphering the chemical structure of bacterial antigens, control of their synthesis by the cell and localization in it, as well as immunogenic specificity is the theoretical basis for creating effective methods for diagnosis and specific immunoprophylaxis of bacterial infections.

The distribution of antigens in a bacterial cell is studied by immunocytological methods - the specific capsule reaction according to J. Tomcsik, the direct and indirect method of fluorescent antibodies, the method of antibodies labeled with ferritin, iodine, mercury or uranium, using electron microscopy of ultrathin sections, as well as isolating individual structures for their subsequent immunological study. To isolate antigens from bacteria, mechanical destruction using small glass beads, ultrasound, high pressure, detergents, lysozyme or bacteriophage are used. Soluble antigenic complexes are extracted from bacteria by treating them with proteolytic enzymes, hot water, trichloroacetic acid, diethyl glycol, phenol, urea, pyridine, ethyl ether, etc. Soluble antigens are purified by gradient ultra-centrifugation using column chromatography or preparative electrophoresis. Highly purified antigens are obtained from enterobacteria, pertussis microbes, streptococci, etc.

Among bacterial antigens, there are type-, species-, group- and genus-specific, as well as “non-specific”. Most type- and group-specific antigens are localized in the flagella, capsule and cell wall of bacteria. Antigens of membranes and intracellular structures of bacterial cells have not been studied enough.

Flagellar antigens (H-antigens) are a protein (flagellin) with a molecular weight of 20,000-40,000, consisting of alpha and beta polypeptide chains. During analytical ultracentrifugation, flagellin forms one homogeneous peak with a sedimentation coefficient of 1.5-1.68. When heated to a temperature of 100° in a strongly acidic or alkaline environment, flagellar antigens are inactivated. It is assumed that the amino acid composition of different serotypes of flagellar antigens of Salmonella, Escherichia and other enterobacteria is different and this determines their type specificity. The classification of Salmonella serotypes is based on the difference in the specificity of flagellar antigens. Isolated flagella of enterobacteria, Vibrio cholerae and other bacteria react as H-antigen (see Bacterial flagella), however, the flagella fraction always contains an admixture of O-antigen. The flagella and flagellin of the S- and R-forms of Proteus mirabilis contain common and different antigenic components. Antigenic specificity depends on the connection and sequence of the flagellin subunits of the flagellar filament. Using the immunodiffusion method (see), two components are detected in the H-antigen. Using preparative immunochemical methods, it is possible to obtain an H-antigen purified from the O-antigen. Purified H-antigen does not have protective activity in experiments on laboratory animals. Soluble flagellar antigens are used for the preparation of erythrocyte H-diagnosticums.

Capsule antigens (K-antigens) many bacteria are type-specific and stimulate specific immunity (see). Many of the capsular antigens are polysaccharides or mucopeptides.

Capsular antigens of pneumococci are type-specific polysaccharides, in isolated form they have the properties of haptens (see Haptens) and are designated as a soluble specific substance (SSS). The capsule of the anthrax pathogen contains a hapten-peptide, as well as antigens of a protein-polysaccharide nature that are sensitive to proteolytic enzymes. Capsular glutamyl polypeptide found in you. megaterium, has the properties of an antigen, cross-reacting with antigens of the cell wall of the same microbe. Capsular antigens of a polysaccharide nature have been identified in microbes of the genus Acetobacter. These antigens cross-reacted with antisera to group B and G streptococci, as well as to type 23 pneumococci. Cross serol, the reaction is due to the presence of a common determinant group in the antigens - L-rhamnose.

Cross-reactions between capsular polysaccharide antigens of group A and B meningococci have been established. pumilus, meningococci group C and E. coli 016: NM, pneumococci type III and E. coli K7, etc.

Polysaccharide antigens were found in the capsule (more precisely microcapsule) of enterobacteria: Vi-antigen (see) in S. typhi, S. paratyphi C, E. coli, E. ballerup, B(K)-antigens in Escherichia, K-antigens in Klebsiella . In some Salmonella, capsular antigens of a protein nature were found that have protective properties (S. typhimurium, S. adelaide, Citrobacter). Capsular polysaccharide antigens of K. pneumoniae have an adjuvant effect (see Adjuvants).

Type-, group-, species- and genus-specific antigens have been identified in the cell wall of many types of microbes. According to Krause's scheme (R. M. Krause, 1963), the cell wall of streptococcus contains type-specific protein antigens (M-substance) and group-specific antigens of a polysaccharide nature. M-antigen (there are up to 60 types) is a protective antigen; in partially purified form, it is proposed as a vaccine. Conducted by Amer. Scientists' testing of a vaccine consisting of partially purified M-antigen showed that the drug caused rheumatism in some vaccinated children. According to a number of authors, the M-antigen is closely related to an antigen that cross-reacts with the human heart muscle antigen. It is assumed that the cross-reacting antigen and M-antigen are different determinants of the same protein molecule. It was also discovered that there is a connection between the M-antigen of group A streptococcus type 1 and the HLA system of human lymphocytes. Another group-specific antigen of the cell wall of streptococci is mucopeptide antigen, the specificity of which is determined by N-acetylglucosamine (for group A streptococci) and N-acetylgalactosamine (for group C streptococci). The group-specific antigen of lactic streptococci is intracellular teichoic acid.

The cell wall of staphylococci contains species-specific antigens - protein A-antigen in the surface layer of the wall and teichoic acid, which, in combination with mucopeptide, makes up the inner layer of the wall. A-antigen is a precipitinogen found in most strains of Staphylococcus aureus, its mol. weight 13,200. It has the ability to enter into a nonspecific reaction with the Fc fragment of class G immunoglobulins in the blood serum of humans and some animals. Teichoic acid is a specific precipitinogen consisting of polyribitol phosphate subunits to which N-acetyl glucose amine (determinant group) and D-alanine are attached. Teichoic acid is found in the cell walls of streptococci, staphylococci, and micrococci. subtilis and lactic acid bacteria. It has been established that teichoic acid isolated from staphylococci has protective properties. From the cell walls of Cl. botulinum type A is a thermostable protein antigen that is resistant to trypsin and has been isolated and purified.

Species- and genus-specific antigens were found in the cell walls of corynebacteria, nocardia, mycobacteria and actinomycetes. The mucopeptide of the cell wall of corynebacteria, nocardia and mycobacteria contains arabinose and galactose, which cause cross-serological reactivity between strains of these groups. Two antigens were identified in the cell wall of the diphtheria microbe: a surface type-specific protein and a deeper group-specific thermostable polysaccharide. A complex set of antigens was identified in the cell wall of anaerobic corynebacteria using radioimmunoelectrophoresis. The main component of the cell walls of these microbes turned out to be an acidic polysaccharide. Group-specific mucopolysaccharide haptens were identified in the cell walls of Bac. anthracis. These haptens react in a precipitation reaction with similar antigens isolated from you. cereus Type-specific antigens of you. megaterium are also localized in the cell wall.

O - antigen (endotoxin) of enterobacteria is localized in the intermediate layer of the cell wall and is a complex compound consisting of a protein or peptide, a polysaccharide and a lipid. Lipopolysaccharide (glucidolipoid complex), extracted by a mixture of phenol and water, has a molecular weight of 106-107, consists of 60-70% phosphorylated polysaccharide and 20-40% lipid (lipid A fatty acids). The molecular weight of the purified polysaccharide is 20,000-60,000. The polysaccharide of O-antigens of different types of enterobacteria is built according to the same principle and consists of a basic structure and S-specific side chains, which are determinant groups. The basic structure (aka R-lipopolysaccharide) of all Salmonella serotypes includes glucosamine, 2-keto-3-deoxyoctanate (KDO), L-glycero-D-manno-heptose, galactose and glucose.

There are 6 known chemotypes of R-lipopolysaccharides identified in the corresponding R-mutants (Ra, Rb, Rc, Rd1, Rd2 and Re), which differ in the degree of defectiveness in the chemical structure. Protein chains include 6-deoxy and especially 3,6-dideoxyhexoses. S-specific side chains are built from repeating oligosaccharides. O factors represent part or all of the determinant group of the O antigen. They are classified according to the Kaufermann-White scheme using cross or homologous agglutination reactions. The terminal sugar that has the greatest affinity for the active site of the antibody is designated as the immunodominant sugar. O-factor 2 (group A) is determined by the immunodominant sugar paratose, O-factor 4 (group B) by abequoise, O-factor 9 (group D) by tyvelose, etc. The immunodominant sugar of Shigella dysenteriae is rhamnose. The specificity of the O-antigen complex is ensured not only by the immunodominant sugar, but also by the sequence of arrangement of sugars in the side chain and the nature of the chemical. bonds between individual sugars. Initially, the basic structure of the polysaccharide is synthesized in the microbial cell, and then the side chains. The lipid part of the O-antigen (lipid A) is almost identical in all enterobacteria. Lipid A is a long chain of fatty acids derived from polyphospho-d-glucosamine and is tightly bound to an O-specific polysaccharide. In this case, the biosynthesis of the polysaccharide molecule, as well as the entire O-antigen molecule, is genetically determined.

The isolated O-antigen (lipopolysaccharide) has a branched structure, which is disrupted when the complex is treated with sodium deoxycholate; so-called hapten subunits are formed, from which, apparently, the entire complex is built. Isolated O-antigens are toxic, pyrogenic, cause local and general Schwartzman phenomenon (see Schwartzman phenomenon), necrosis of tumor tissue, specific and nonspecific resistance, and also have immunostimulating and immunosuppressive activity. It is assumed that the toxic activity of O-antigens is due to lipid A. Administration of O-antigen to animals is accompanied by leukopenia and thrombocytopenia. O-antigen causes the phenomenon of tolerance, accompanied by a noticeable increase in phagocytic activity. In addition to the O-antigen, heat-labile antigens, as well as general antigens, were found in the cell walls of enterobacteria.

In 1962, S. Kunin and co-authors first described the common antigen of enterobacteria, which differs in specificity from the O-antigen. The common antigen extracted from E. coli 014, a polysaccharide, causes the production of specific antibodies in rabbits.

Lipopolysaccharide, or lipid A, administered to an animal along with a common antigen, suppresses the production of antibodies to the common antigen. Another type of common antigen, called C-antigen, was found in E. coli and Sh. sonnei. Sh. sonnei, using the hemagglutination reaction, a bacterial agglutinogen (BA) associated with lipopolysaccharide was identified. In 1969, E. Engelbrecht reported another common antigen in enterobacteria, the “alcoholophilic” factor, which was obtained from S. paratyphi A and B, S. bareilly. It is assumed that the “alcoholic” antigen is a polysaccharide. A specific alpha antigen is localized in the cell walls of Vibrio cholera, a protective protein antigen and a histamine-sensitizing factor are localized in the causative agent of whooping cough, and an antigen extracted by a phenol-water mixture and traces of fraction I are localized in the plague microbe.

The protective activity of isolated cell walls was demonstrated in experiments with staphylococci, streptococci, tularemia microbes, the causative agent of plague, enterobacteria, pertussis microbes, mycobacteria, Vibrio cholerae, and Brucella. Soluble antigens with protective activity are extracted from the cell walls of these microbes. The cell walls of many gram-positive and gram-negative microbes cause the formation of granules, dermatitis, hepatitis, chronic carditis and arthritis in laboratory animals. In in vitro experiments, cell walls stimulate the release of lysosomal enzymes, have a cytotoxic effect, and inhibit bacterial flucytosis and cell growth.

Thus, the surface structures of many bacteria contain type-, group-, species- and genus-specific antigens, as well as common antigens for different types of microbes. Many of the listed antigens are important in the pathogenesis of diseases and the formation of specific immunity.

Antigens of membranes and intracellular structures. Specific antigens are concentrated in bacterial membranes. So, antigens of the cytoplasmic membrane B. megaterium differ in their specificity from cell wall antigens.

A study of the antigenic structure of Micrococcus lysodeicticus membranes showed that there are 8 antigens located on the surface of the cytoplasmic membrane. O- and H-antigens, as well as unidentified antigens, were found in the membrane fraction of E. coli 0111: K 4: H12 and other enterobacteria. It has been established that the O-antigen of membranes is identical to the O-antigen of cell walls. The H-antigen of membranes is identical to the H-antigen of isolated flagella, since the basal part of the flagellum is attached or located on the inner surface of the cytoplasmic membrane. Therefore, the H-antigenic activity of membranes is due to the antigenic activity of the basal part of the flagellum. Proteins extracted from the membranes of mycoplasmas of different serola groups had specific antigenic activity. A rod-shaped structure with a sedimentation coefficient of 22s, which has protective properties (223-antigen), was isolated from the pertussis microbe destroyed by ultrasound. This antigen is probably localized in membranes. A new class of bacterial antigen has been described - lipoteichoic acid, which can be isolated from streptococci, lactic acid bacteria and some bacilli. Lipoteichoic acid is localized on the surface of the cytoplasmic membrane and is a group-specific antigen. Lipoteichoic acid is composed of 25-30 glycerophosphate residues and a lipid component (glycolipid). Some glycerophosphate residues are replaced by glucose and D-alanine. Membrane antigens of most pathogenic bacteria have been poorly studied.

The cytoplasmic fraction of bacteria is distinguished by a certain originality: along with cytoplasmic components (ribosomes, granules, fragments of the endoplasmic reticulum, cell sap), it contains nuclear components (DNA and, possibly, nuclear proteins).

Therefore, when subjecting the cytoplasmic fraction immunol to analysis, it is sometimes difficult to say due to which antigens the activity was detected.

The so-called total fraction of the cytoplasm of enterobacteria, pertussis microbes, cocci and other bacteria has weak antigenic activity. Common antigens were found in the cytoplasm of a number of bacteria: between strains of the genus Nocardia and Streptomyces, Nocardia and Mycobacterum. Identical cytoplasmic antigens have been identified in mycobacteria, actinomycetes and corynebacteria. However, specific antigens were found in the cytoplasm of the plague microbe: fraction I, “mouse” toxin, VW antigen and an antigenic complex extracted by trichloroacetic treatment. The listed antigens may be important in the pathogenesis of infection. Using a model of a plague microbe, it was shown that the antigenic complexes obtained by the phenol-water method and the antigenic complex extracted by trichloroacetic acid are different antigens and, possibly, localized in different structures. From an ultrasonic lysate of Shigella, Seltman (G. Seltman, 1975) isolated an antigen moving to the anode (ATA), which turned out to be common to many enterobacteria. This protein antigen is probably located inside the cell.

Antigens were identified in ribosomes: during 1960-1963, it was found that three types of antigens are localized in bacterial ribosomes, common to many bacteria (apparently RNA), common to a limited number of species (protein) and specific to each species. In 1967-1975, it was shown that ribosomal fractions obtained from enterobacteria, listeria, mycobacteria, pertussis microbes, vibrios cholerae, and staphylococci have protective properties in experiments on laboratory animals. It has been proven that the protective activity of ribosomes is not associated with the admixture of cell wall antigens. A protein that had specific protective properties was isolated from the ribosomal fraction of Vibrio cholerae using ion exchange chromatography, and purified ribosomes did not cause protection in animals. However, some researchers suggest that the protective activity of ribosomes is associated with RNA, others with protein, and still others believe that some kind of carbohydrate, possibly from the cell wall, which has the specific properties of an antigen, is “attached” to isolated ribosomes. The mechanism of the protective effect of “ribosomal” vaccines is not clear.

Research by E. Ribi et al. It was demonstrated the presence in the cytoplasm of enterobacteria of a low molecular weight polysaccharide, which, due to its antigenic properties and chemical properties. composition is close to the O-antigen of the cell wall. This polysaccharide is described as plasmatic. Its antigenic activity appears only when it is combined with the O-antigen. However, such a complex does not induce the formation of antibodies in rabbits. The plasmatic polysaccharide was designated as a native hapten, built from “linear molecules” (particles) with a molecular weight of 163,000, a diameter of 1.6 nm, and a length of 130 nm. Molecules of native hapten, unlike O-antigen, do not form micellar structures. It has been suggested that the native hapten is a precursor of the cell wall O-antigen.

Many researchers have found that bacterial DNA has antigenic properties. Bacterial DNA preparations react as antigens with homologous and heterologous sera. Serol cross-reactivity is shown between the DNA of bacteria and the DNA of cells of the macroorganism.

Some researchers believe that bacterial DNA and nucleoproteins stimulate the autoimmune process.

Thus, bacteria have a complex mosaic of antigens that are distributed in almost all structures and organelles. Some of these antigens are more active, others less so. The most important from a practical point of view is the issue of identifying and isolating protective antigens in purified form for the purpose of producing effective vaccines and diagnostic drugs.

Bibliography: Anatomy of bacteria, trans. from English, ed. G. P. Kalina, M., 1960; Ierusalimsky N.D. Fundamentals of microbial physiology, M., 1963, bibliogr.; Metabolism of bacteria, trans. from English, ed. V.A. Shorina, M., 1963, bibliography; Multi-volume guide to microbiology, clinic and epidemiology of infectious diseases, ed. N. N. Shukova-Verezhnikova, vol. 1, p. 58 and others, M., 1962; Peshkov M.A. Cytology of bacteria, M.-JI., 1955, bibliogr.; aka, Comparative cytology of blue-green algae, bacteria and actinomycetes, M., 1966; Rose E. Chemical microbiology, trans. from English, M., 1971, bibliogr.; Stanislavsky E. S. Bacterial structures and their antigenicity, M., 1971, bibliogr.; Bergey's manual of determinative bacteriology, ed. by R. E. Buchanan a. N. E. Gibbons, Baltimore, 1975, bibliogr.; Annual Review of Microbiology, v. 1-26. Stanford, 1957-1972; Bacteria, ed. by I. C. Gunsalus a. R. Y. Stani-er, v. 1-5, N. Y.-L., 1960-1964; Helms tetter C.E. Sequence of bacterial reproduction, Ann. Rev. Microbiol., v. 23, p. 223, 1969, bibliogr.; K a em p-fer R. a. Meselson M. Studies of ribosomal subunit exchange, Cold Spr. Harb. Symp. quant. Biol., v. 34, p. 209, 1969; Korn E.D. Cell membranes, structure and synthesis, Ann. Rev. Biochem., v. 38, p. 263, 1969; N o m u r e M. Bacterial ribosome, Bact. Rev., v. 34, p. 49, 1970; About s-born M. J. Structure and biosynthesis of the bacterial cell wall, Ann. Rev. Biochem., v. 38, p. 501, 1969; Replication of DNA in microorganisms, Cold Spr. Harb. Symp. quant. Biol., v. 33, 1968; R y t e r A. Association of the nucleus and membrane of bacteria, Bact. Rev., v. 32, p. 39, 1969; T o p 1 e at W. W. a. Wilson G. S. Principles of bacteriology and immunity, v. 1 - 2, Baltimore, 1964.

Genetics B.- Brown V. Genetics of bacteria, trans. from English, M., 1968, bibliogr.; Jacob F. and Wolman E. Sex and genetics of bacteria, trans. from English, M., 1962; Zakharov I. A. and Kvitko K. V. Genetics of microorganisms, JI., 1967; Collection of methods on the genetics of microorganisms, ed. R. Klaus and W. Hayes, trans. from English, M., 1970, bibliogr.; S to a-vronskaya A.G. Mutations in bacteria, M., 1967, bibliogr.; T a y 1 o g A. Z. a. T g about t-t e r C. D. Linkage map of Escherichia coli strain K-12, Bact. Rev., v. 36, p. 504, 1972, bibliogr.; CurtissR. Bacterial conjugation, Ann.Rev. Microbiol., v. 23, p. 69, 1969; Hartman P.E., Hartman Z.a. Stahl R. Classification and mapping of spontaneous and induced mutations in the histidine operon of Salmonella, Advanc. Genet., v. 16, p. 1, 1971, bibliogr.; Proceedings of the 12th international congress of genetics, v. 3, Tokyo, 1968; Sanderson K. E. Genetics of the Enterobacteriaceae, Advanc. Genet., v. 16, p. 35, 1971, bibliogr.

Antigens of bacteria- Ado A.D. and Fedoseeva V.N. Localization in the cells of Neisseria perflava and Klebsiella pneumoniae of antigens common (cross-reacting) with the tissues of the human bronchopulmonary apparatus, Bull. Experiment, biol, and med., t. 81, Kya 3, p. 349, 1976; Goldfarb D.M. and Zamchuk L.A. Immunology of nucleic acids, M., 1968, bibliogr.; M and x and y-l about in I. F. Fluorescent antibodies and methods of their use, M., 1968, bibliogr.; Petrosyan E. A. Complex antigens of the typhoid-paratyphoid group of bacteria, M., 1961, bibliogr.; Stanislavsky E. S. Bacterial structures and their antigenicity, M., 1971, bibliogr.; H e u m e r V., S p a n e 1 R. a. Haferkamp O. Biologische Aktivitat bakterieller Zellwande, Immun. u. Infekt., Bd 3, S. 232, 1975; Luederitz O. a. o. Isolation and chemical and immunological characterization of bacterial lipopoly-saccharides, in: Microbial toxins, ed. by T. C. Montie, v. 4, p. 145, N.Y., 1971, bibliogr.; Owen P. a. Salton M. Antigenic and enzymatic architecture of Micrococcus lysodeikticus membranes established by crossed immunoelectrophoresis, Proc. nat. Acad. Sci. (Wash.), v. 72, p. 1711, 1975; Robbins J. B. a. o. Gross-reacting bacterial antigens and immunity to disease caused by encapsulated bacteria, in the book: Immun. syst. a. infect. Dis., ed. by E. Ne-ter a. F. Milgrom, p. 218, Basel a. o., 1975; Wicken A. J. a. Knox K. W. Lipoteichoic acids, a new class of bacterial antigen, Science, v. 187, p. 1161, 1975.

B. S. Levashev; A. G. Skavronskaya (gen. from table); D. M. Goldfarb (bacterial table). E. S. Stanislavsky.

Bacteria are the most ancient organism on earth, and also the simplest in their structure. It consists of just one cell, which can only be seen and studied under a microscope. A characteristic feature of bacteria is the absence of a nucleus, which is why bacteria are classified as prokaryotes.

Some species form small groups of cells; such clusters may be surrounded by a capsule (case). The size, shape and color of the bacterium are highly dependent on the environment.

Bacteria are distinguished by their shape into rod-shaped (bacillus), spherical (cocci) and convoluted (spirilla). There are also modified ones - cubic, C-shaped, star-shaped. Their sizes range from 1 to 10 microns. Certain types of bacteria can actively move using flagella. The latter are sometimes twice the size of the bacterium itself.

Types of forms of bacteria

To move, bacteria use flagella, the number of which varies—one, a pair, or a bundle of flagella. The location of the flagella can also be different - on one side of the cell, on the sides, or evenly distributed throughout the entire plane. Also, one of the methods of movement is considered to be sliding thanks to the mucus with which the prokaryote is covered. Most have vacuoles inside the cytoplasm. Adjusting the gas capacity of the vacuoles helps them move up or down in the liquid, as well as move through the air channels of the soil.

Scientists have discovered more than 10 thousand varieties of bacteria, but according to scientific researchers, there are more than a million species in the world. The general characteristics of bacteria make it possible to determine their role in the biosphere, as well as to study the structure, types and classification of the bacterial kingdom.

Habitats

Simplicity of structure and speed of adaptation to environmental conditions helped bacteria spread over a wide range of our planet. They exist everywhere: water, soil, air, living organisms - all this is the most acceptable habitat for prokaryotes.

Bacteria were found both at the south pole and in geysers. They are found on the ocean floor, as well as in the upper layers of the Earth's air envelope. Bacteria live everywhere, but their number depends on favorable conditions. For example, a large number of bacterial species live in open water bodies, as well as soil.

Structural features

A bacterial cell is distinguished not only by the fact that it does not have a nucleus, but also by the absence of mitochondria and plastids. The DNA of this prokaryote is located in a special nuclear zone and has the appearance of a nucleoid closed in a ring. In bacteria, the cell structure consists of a cell wall, capsule, capsule-like membrane, flagella, pili and cytoplasmic membrane. The internal structure is formed by cytoplasm, granules, mesosomes, ribosomes, plasmids, inclusions and nucleoid.

The cell wall of a bacterium performs the function of defense and support. Substances can flow freely through it due to permeability. This shell contains pectin and hemicellulose. Some bacteria secrete a special mucus that can help protect against drying out. Mucus forms a capsule - a polysaccharide in chemical composition. In this form, the bacterium can tolerate even very high temperatures. It also performs other functions, such as adhesion to any surfaces.

On the surface of the bacterial cell there are thin protein fibers called pili. There may be a large number of them. Pili help the cell pass on genetic material and also ensure adhesion to other cells.

Under the plane of the wall there is a three-layer cytoplasmic membrane. It guarantees the transport of substances and also plays a significant role in the formation of spores.

The cytoplasm of bacteria is 75 percent made from water. Composition of the cytoplasm:

• Fishsomes;
• mesosomes;
• amino acids;
• enzymes;
• pigments;
• sugar;
• granules and inclusions;
• nucleoid.

Metabolism in prokaryotes is possible both with and without the participation of oxygen. Most of them feed on ready-made nutrients of organic origin. Very few species are capable of synthesizing organic substances from inorganic ones. These are blue-green bacteria and cyanobacteria, which played a significant role in the formation of the atmosphere and its saturation with oxygen.

Reproduction

In conditions favorable for reproduction, it is carried out by budding or vegetatively. Asexual reproduction occurs in the following sequence:

1. The bacterial cell reaches its maximum volume and contains the necessary supply of nutrients.
2. The cell lengthens and a septum appears in the middle.
3. Nucleotide division occurs inside the cell.
4. The main and separated DNA diverge.
5. The cell divides in half.
6. Residual formation of daughter cells.

With this method of reproduction, there is no exchange of genetic information, so all daughter cells will be an exact copy of the mother.

The process of bacterial reproduction under unfavorable conditions is more interesting. Scientists learned about the ability of sexual reproduction of bacteria relatively recently - in 1946. Bacteria do not have division into female and reproductive cells. But their DNA is heterogeneous. When two such cells approach each other, they form a channel for the transfer of DNA, and an exchange of sites occurs - recombination. The process is quite long, the result of which is two completely new individuals.

Most bacteria are very difficult to see under a microscope because they do not have their own color. Few varieties are purple or green in color due to their bacteriochlorophyll and bacteriopurpurin content. Although if we look at some colonies of bacteria, it becomes clear that they release colored substances into their environment and acquire a bright color. In order to study prokaryotes in more detail, they are stained.

Classification

Classification of bacteria can be based on indicators such as:

• Form
• way to travel;
• method of obtaining energy;
• waste products;
• degree of danger.

Bacteria symbionts live in community with other organisms.

Bacteria saprophytes live on already dead organisms, products and organic waste. They promote the processes of rotting and fermentation.

Rotting cleanses nature of corpses and other organic waste. Without the process of decay there would be no cycle of substances in nature. So what is the role of bacteria in the cycle of substances?

Rotting bacteria are an assistant in the process of breaking down protein compounds, as well as fats and other compounds containing nitrogen. After carrying out a complex chemical reaction, they break the bonds between the molecules of organic organisms and capture protein molecules and amino acids. When broken down, the molecules release ammonia, hydrogen sulfide and other harmful substances. They are poisonous and can cause poisoning in people and animals.

Rotting bacteria multiply quickly in conditions favorable to them. Since these are not only beneficial bacteria, but also harmful ones, in order to prevent premature rotting of products, people have learned to process them: drying, pickling, salting, smoking. All these treatment methods kill bacteria and prevent them from multiplying.

Fermentation bacteria with the help of enzymes are able to break down carbohydrates. People noticed this ability back in ancient times and still use such bacteria to make lactic acid products, vinegars, and other food products.

Bacteria, working together with other organisms, do very important chemical work. It is very important to know what types of bacteria there are and what benefits or harm they bring to nature.

Meaning in nature and for humans

The great importance of many types of bacteria (in the processes of decay and various types of fermentation) has already been noted above, i.e. fulfilling a sanitary role on Earth.

Bacteria also play a huge role in the cycle of carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium and other elements. Many types of bacteria contribute to the active fixation of atmospheric nitrogen and convert it into organic form, helping to increase soil fertility. Of particular importance are those bacteria that decompose cellulose, which is the main source of carbon for the life of soil microorganisms.

Sulfate-reducing bacteria are involved in the formation of oil and hydrogen sulfide in medicinal mud, soils and seas. Thus, the layer of water saturated with hydrogen sulfide in the Black Sea is the result of the vital activity of sulfate-reducing bacteria. The activity of these bacteria in soils leads to the formation of soda and soda salinization of the soil. Sulfate-reducing bacteria convert nutrients in rice plantation soils into a form that becomes available to the roots of the crop. These bacteria can cause corrosion of metal underground and underwater structures.

Thanks to the vital activity of bacteria, the soil is freed from many products and harmful organisms and is saturated with valuable nutrients. Bactericidal preparations are successfully used to combat many types of insect pests (corn borer, etc.).

Many types of bacteria are used in various industries to produce acetone, ethyl and butyl alcohols, acetic acid, enzymes, hormones, vitamins, antibiotics, protein-vitamin preparations, etc.

Without bacteria, the processes of tanning leather, drying tobacco leaves, producing silk, rubber, processing cocoa, coffee, soaking hemp, flax and other bast-fiber plants, sauerkraut, wastewater treatment, leaching of metals, etc. are impossible.