Type 1 drank

Type 1 pili are firmly attached to the cell, and in order to detach them from it, considerable effort is required, greater than to remove flagella or sex pili. Pili of this type are also resistant to chemical influences - they are preserved in 6 M urea, 1 M NaOH, and are resistant to sodium dodecyl sulfate and trypsin. These pili are destroyed only when boiled in a low-value solution, which causes irreversible denaturation of the protein. The protein that forms the general type 1 pili has a molecular mass of 17 kDa.

Type 1 pili are located peritrichially, that is, along the entire surface of the bacterium. One cell can have 50-400 pili up to 1.5 microns long. The diameter of these pili is about 7 nm, and the holes are 2.0-2.5 nm.

The formation of general type 1 pili is determined by genes located on the chromosome. Their activity is subject to phase variations, that is, the gene can be active or not. Typically, a culture contains both cells that have many common type 1 pili and those that lack them. Cells that are in one phase or another can be easily removed. The proliferation of cells lacking pili is promoted by growing the culture on agar, while cells with pili benefit from growing the culture in a liquid medium without aeration. In doing so, they form a film. Type 1 pili impart hydrophobicity to bacteria and reduce their electrophoretic mobility. They cause agglutination of red blood cells due to the fact that such bacteria adhere to red blood cells (as well as to other animal cells), as well as to plant and fungal cells, and to inorganic particles. In the presence of mannose, hemagglutination and bacterial attachment to animal cells in general are impaired, as type 1 pili attach to surface receptors containing mannose. In the presence of mannose, the corresponding pili areas are occupied by its molecules. The adhesiveness of pili also depends on the hydrophobicity of the pilin protein that forms them. Areas of pili located throughout their surface react with mannose receptors, while the endings of pili are responsible for hydrophobic interactions.

Type 2 drank

Type 2 pili are similar to type 1 pili, but do not cause agglutination of red blood cells and do not contribute to the formation of a film by bacteria in a liquid medium. Antigenically they are close to type 1 pili and, apparently, represent their mutant form. A number of other variants of saws close to type 1 saws have also been described. Associations of common type 1 pili with pathogenicity in strains E. coli cannot be detected. Enteropathogenic strains usually produce other pili encoded by plasmid genes. Several types of such pili are known, and a connection is found between the type of pili and the specificity of bacteria in relation to certain animals.

Other types of saws

The pili, known as K88 and K99 antigens, are thinner and more labile than type 1 pili. They cause mannose-resistant hemagglutination and promote bacterial attachment to intestinal epithelial cells in animals, but not humans. Pili 987P determine the ability E. coli attach to the epithelium of the small intestine of newborn pigs; morphologically they are similar to type 1 pili. Pili, determined by the genetic factor CFA/1, cause agglutination of human erythrocytes and are found in strains pathogenic for humans. The molecular weight of pilin proteins encoded by plasmid genes is 14.5-26.2 kDa. In enteropathogenic strains of E. coli, pili are one of the pathogenicity factors that provide them with the ability to attach to intestinal epithelial cells. Colonization of the epithelium by bacteria promotes the effective interaction of the enterotoxin they secrete with epithelial cells. As a result, tissue water metabolism is disrupted, which clinically manifests itself as diarrhea. In this case, bacteria multiply vigorously in the small intestine and are then released into the environment in large numbers, which contributes to their spread.

Sexual drank

Sex drank E. coli are formed in cells of donor strains that differ from isogenic recipient strains by the presence in the cells of a special genetic determinant - a sex factor, or transmissibility factor, which is either an autonomous replicon (F-factor), or is part of an autonomous replicon, or is integrated with the bacterial chromosome. The transmissibility factor is found in plasmids - multiple antibiotic resistance factors (R-factors), colicinogenicity factors and a number of other plasmids. Sexual pili differ from general pili in structure and antigenic specificity; pili encoded by various genetic determinants are also different.

Sexual F-pili, determined by F-factors, are protein cylinders perpendicular to the cell surface, 8.5-9.5 nm thick and up to 1.1 µm long. They can easily be separated from the cell by shaking the bacterial mass. F-pili are formed by a protein with a molecular weight of 11.8 kDa. F-pilin does not contain proline, cysteine, histidine, or arginine. Attached to the pilin molecule are two phosphate groups and a D-glucose residue, linked to the protein by covalent bonds. Pilin contains quite a lot of acidic and hydrophobic amino acids. It is synthesized on ribosomes associated with the cytoplasmic membrane and is not found in the cytoplasm. The pilin pool appears to accumulate in the cytoplasmic membrane. During synthesis, its molecules contain an additional signal sequence of amino acids, which is cleaved off during transport through the membrane. F-pili easily dissociate in sodium dodecyl sulfate solutions and are destroyed by organic solvents, which is due to the hydrophobicity of pilin. Bacteria that have F-pili acquire a new antigen and their surface charge changes. Bacteria with F-piles are inactive and tend to auto-agglutinate, for example, when the pH value of the medium decreases. This is also due to the richness of pilin in acidic and hydrophobic amino acids. The F factor is also interesting because sometimes (in about 1 case out of 100,000) it is integrated into the main DNA molecule of the host cell. Then, during conjugation, not only the F factor is transferred, but also the rest of the DNA. This process takes approximately 90 minutes, but the cells can separate earlier, before the DNA is completely exchanged. Such strains continually transfer all or most of their DNA to other cells. These strains are called Hrf (High frequency recombination) strains because the donor DNA of such strains recombines with the recipient DNA.

The formation of F pili requires the activity of at least 13 genes. The assembly of pili tubes occurs on the cytoplasmic membrane at the points of its contact with the outer membrane. The pili tube passes through the murein layers and the outer membrane. Energy is required to assemble and maintain the pili. The formation of pili is prevented by cyanide, dinitrophenol, and sodium azide. It is possible that phosphorylation of pilin occurs during the assembly process. Typically, cells with derepressed F factor form 1-2 pili, and under anaerobic conditions and in a rich medium - up to 5 pili. The reason for the stimulation of pile formation under anaerobic conditions is unknown. Cells with torn pili quickly grow new ones; in 30 seconds the pili reaches 1/2 of its normal length, and is completely formed in 4-5 minutes. The formed pili remain on the cell surface for 4-5 minutes and are then discarded. This testifies in favor of the point of view that they drank - active formations. Pili determined by the Col I factor are formed by a different pilin; phages specific for F-pili are not adsorbed on them, but there are phages specific for them. The so-called male phages are adsorbed on the sex pili, RNA-containing phages on their side surfaces, and filamentous phages containing single-stranded DNA on the tips of these pili. The filamentous phage prevents conjugation.

During conjugation, the end of the sex pili attaches to the recipient cell, and the receptor is the protein of the outer membrane of the recipient cell. At first, this contact is not very strong and can easily be broken by hydrodynamic influences. In this case, the pairs break up during multiple infections with RNA-containing phages or in the presence of Zn 2+ ions. After a few minutes, the contact becomes stronger, the cells come closer together and a cytoplasmic bridge forms between them. There is evidence that DNA transfer can occur without the formation of a cytoplasmic bridge, but directly through the hole in the saw. Inactivation of pili by antiserum and any damaging effects on them lead to disruption of the conjugation process, while disruption of the integrity of the outer membrane or murein layer affects the donor properties of the cell having pili to a certain extent. After establishing contact with the recipient cell, the worm pili transmits a signal to the donor cell, causing the onset of conjugative DNA synthesis. The mechanism of operation of sexual saws has not yet been fully established. A number of observations support a model that assumes the active function of pili. According to this view, after contact is made with a recipient cell or with a virus, the pili contracts or is retracted into the cell. This model is supported by both indirect and direct observations. In electron microscopic preparations, one can observe how, after the adsorption of filamentous male phage on their tips, the pili are shortened, and then the phage filaments appear on the cell surface. Pili contraction is caused by KCN or arsenate. After exposure to these inhibitors, pili are not detected either on the surface of cells or in the environment, but adsorption of male phages and antibodies specific to the ends of pili can be observed on the cell surface, that is, their tips apparently continue to protrude above the cell surface. During phage infection, the protein shell of the filamentous phage subsequently dissolves in the cytoplasmic membrane of the bacterium and its DNA is released into the cytoplasm. When infected with RNA-containing male phages, a complex of phage RNA with pilin is first formed, and the phage capsid is released into the medium.

Typically, pilin synthesis is under the control of cytoplasmic repressors. In some cases, it is possible to observe certain patterns in the regulation of pili formation. Thus, in the case of the Col I factor, each cell that received the Col I plasmid during conjugation forms pili; their active formation occurs in cells of 4-8 subsequent generations. However, then only a few cells in the population form pili, since pilin synthesis is repressed in most bacteria. Such repression is believed to have adaptive significance, since cells without pili are not sensitive to male bacteriophages, which could destroy the entire population. Single cells with pili are capable of providing conjugation. When such cells come into contact with populations of recipient bacteria, an avalanche-like spread of the plasmid begins, since the formation of pili is not initially repressed.

Sex pili usually form only in actively growing cells; cells from a culture in the stationary growth phase usually lack pili and are poor donors.

As already noted, there are many more or less different plasmids capable of determining the formation of sex pili, which are also somewhat different. Receptors on the surface of recipient cells have different degrees of affinity for different pili, which can greatly influence the efficiency of bacterial conjugation.

Drank like saws E. coli, form other representatives Enterobacteriaceae. Sexual pili have Vibrio, Pasteurella, Aeromonas, Pseudomonas.

On the cell surface of many prokaryotes there are structures that determine the ability of a cell to move in a liquid environment. This - flagella . Their number, size, location, as a rule, are characteristics that are constant for a particular species, and therefore are taken into account in the taxonomy of prokaryotes. However, evidence is accumulating that the number and location of flagella in the same species can be largely determined by culture conditions and stage life cycle, and, therefore, the taxonomic significance of this character should not be overestimated.

If flagella are located at the poles or in the polar region of the cell, they are said to be polar or subpolar location, if along the lateral surface, they talk about lateral location.

Flagella are long shoots, which extend from one (monotrichs, lophotrichs) or both (amphitrichs) poles of the bacterial cell or are distributed over its entire surface (peritrichs). Like fimbriae, flagella consist of polymerized or tightly folded protein subunits that give them toughness spiral shape and cause serological differences different types bacteria.

In some spirochetes, for example Treponema pallidum and Borrelia burgdorferi, longitudinally located flagella are collected into an axial filament. Thanks to this formation, which spirals around the cell, spirochetes can actively move using rotational movements. Some bacteria can move along the substrate without visible motor structures.

Depending on the number of flagella and their location on the cell surface, they are divided into:

• monopolar monotrichs (one flagellum attached to one pole of the cell;
• monopolar polytrichs (a bundle of flagella is located at one pole of the cell), bipolar polytrichs (a bundle of flagella at each pole;
• peritrichous (numerous flagella located over the entire surface of the cell or along its lateral surface.

In the latter case, the number of flagella can reach 1000 per cell.

The usual thickness of the flagellum is 10-20 nm, length - from 3 to 15 µm. In some bacteria, the length of the flagellum can be an order of magnitude greater than the diameter of the cell. As a rule, polar flagella are thicker than peritrichous flagella.

The flagellum is a relatively rigid spiral, usually twisted counterclockwise. The flagellum also rotates counterclockwise with a frequency of 40 to 60 rps, which causes the cell to rotate, but in the opposite direction. Since the cell is much more massive than the flagellum, it rotates at a much lower speed - about 12-14 rpm. The rotational movement of the flagellum is also converted into translational movement of the cell, the speed of which in a liquid medium for different types of bacteria ranges from 16 to 100 μm/s.

Studying the structure of the flagellum under an electron microscope revealed that it consists of three parts. The main mass of the flagellum is a long spiral thread (fibril), which at the surface of the cell wall turns into a thickened curved structure - hook. The thread is attached with a hook to the basal body, embedded in the CPM and the cell wall. The protein subunits are arranged in the form of a spiral, inside which there is a hollow channel. The flagellum grows from the distal end, where the subunits enter through the internal channel. In some species, the outside of the flagellum is additionally covered with a special sheath. chemical structure or being a continuation of the cell wall and probably constructed of the same material.

The surface structures of a bacterial cell also include fimbriae (pili, cilia, villi) - hard, straight, hollow filaments of the pilin protein, localized on the CS. Fimbriae are shorter and thinner than flagella: their diameter is 3–20 nm, length 0.2–10.0 µm.

Fimbriae - optional cellular structure, since bacteria grow and reproduce well without them. Unlike flagella, fimbriae do not perform a motor function and are found in motile and immobile forms. According to their functional purpose, fimbriae are divided into 2 types. The term "fimbriae" is more commonly used to refer to the common pili, and the term "pili" to refer to the sex pili.

Fimbriae 1 (general) type found in most bacteria. They cover the entire surface of the cell and are located peritrichially or polarly. The number of fimbriae is large - from several hundred to several thousand per bacterial cell. The synthesis of fimbriae is controlled by the bacterial chromosome; the loss of fimbriae leads to their new synthesis.

Covering the entire cell, fimbriae create a fleecy surface. Sometimes the fimbriae merge into lumps, giving the cell an untidy appearance; in other cases, the surface of the cells is covered with a felt-like cover, consisting of plexuses of thin filaments.

Drank 2 types(synonyms: conjugative, sexual, sex pili) are formed only by male donor cells containing transmissible plasmids (F, R, Col), in limited quantities (1–4 per cell), and have terminal swellings.

Functions of fimbriae.

Fimbriae of both types:

• They have antigenic activity.
• Bacteriophages (specific bacterial viruses) are adsorbed on them.
• Adhesive function: ensure the attachment of bacteria to the cells of the mucous membranes of the host body and to other substrates (cells of plants, fungi, inorganic particles and organic residues).
• Mechanical protection of the bacterial cell. They give bacteria the property of hydrophobicity and promote the union of cells into groups.
• They increase the absorption surface of bacterial cells, participate in nutrition processes, water-salt metabolism and in the transport of metabolites.

Sex pili: F-pili provide conjugation - the transfer of part of the genetic material from the donor cell to the recipient cell.

Drank

On the surface of a prokaryotic cell there are often thread-like formations of a protein nature, which are called pili or fimbriae (from the Latin words “hair”, “thread”). The pili of gram-negative bacteria have been studied in sufficient detail, and the existence of pili in gram-positive organisms is also known.

They are responsible for attaching a cell to a nonliving object and to another cell, help receive and transfer DNA during conjugation, and serve as acceptors for bacteriophages. The main purpose of the pili is to support the specific attachment structures of the cell. Attachment subunits (adhesins) are often present as minor components at the ends of the pili, but the main structure of the pili can also act as an adhesin. Adhesins act as mediators during bacterial contacts, contacts with non-living objects, tissues and cells in susceptible organisms. Colonization of host tissues by pathogenic bacteria generally depends on the stereochemical similarity between the architecture of the adhesin and the corresponding host cell receptor. The relationships mediated by adhesive pili can aid in the formation of microbial biofilms and are often a major factor in the successful colonization of the host by pathogenic and saprotrophic microorganisms. Yes, uropathogenic E. coli for effective colonization of the epithelium Bladder must have type 1 pili. These pili attach to conserved mannose-containing receptors on bladder epithelial cells and prevent bacteria from being washed out in the urine. P-pili perform the same function in the kidneys, preventing the removal of cells that cause pyelonephritis E. coli from the kidneys and urinary canals. Intestinal pathogens form numerous and varied adhesive pili that help the bacteria colonize the intestine. This group includes pili K88, K99, 987P, long polar fimbriae, plasmid pili Salmonella enterica and aggregating fimbriae of eitheropathogenic E. coli. TC P-pili are responsible for attachment V. cholerae to the epithelium of the small intestine. These same pili act as receptors for the lysogenic phage encoding two subunits of cholera toxin. This phage is transferred in the small intestine between Vibrio cholerae cells using TCP pili. Other pili also assist in the acquisition of virulence factors. DNA uptake occurs through type 4 pili, and DNA transfer occurs through conjugative pili, which help pathogenic microorganisms acquire genes that allow them to synthesize a wide range of virulence factors and give them resistance to many antibiotics. The formation of biofilms, which in many cases requires the participation of pili types 1, 4 or "curls", also protects pathogenic bacteria from action medicines and may promote colonization of tissues and medical implants. There are a number of examples where the attachment of pili caused the appearance of signals in host cells. Attachment of genus cells Neisseria via type 4A pili to host epithelial cell receptors, causes the release of stored intracellular Ca 2+ , known as a signal that regulates eukaryotic cell responses. The attachment of P-pili to uroepithelial cells can cause the release of ceramides, important second messengers that can activate a number of protein kinases and phosphatases involved in signal transduction. These signals ultimately lead to the cells releasing cytokines. Pili can also transmit a signal into the host cell. It has been shown that the attachment of P-pili to host cell receptors stimulates the activation of iron-mobilizing mechanisms in uropathogenic E. coli. This likely increases the ability of pathogen cells to obtain iron and survive in the iron-deficient environment of the urinary system. Thus, studying the functioning of pili will allow not only a deeper understanding of the mechanisms of colonization and signal transmission, but also the development of new generations of antimicrobial agents to combat pathogenic microorganisms.

The architecture of pili varies from thin thread-like to thick, strong rod-shaped structures with axial holes. Thin pili with a diameter not exceeding 2-3 nm, such as K88 and K99, are often classified as fibrils. Even thinner pili (E. coli and Haemophilus influenzae are complex structures consisting of a thick rod with a thin fibril attached to it. The location of the pili can be different (along the entire surface of the cell or only at the end). Pili are often located peritrichial along the cell surface, but type 4 pili may be localized at only one end of the cell. One cell may have fimbriae different types. The length of the pili ranges from 0.1 to 20 μm, and the diameter from 2 to 11 nm.

Pili are composed of one or more types of protein subunits called pilins (fimbrins), which are usually arranged in a helical pattern. To assemble pili at the cell surface, all pilins must be transferred across the inner membrane, periplasm, and outer membrane. This process in all bacteria requires two specialized assembly proteins - the periplasmic chaperone and the outer membrane doorman. The chaperone-doorman ensemble is involved in the biogenesis of more than 30 different structures, including complex pili, fine fibrils, and nonfibril adhesins.

The structure of bacteria has been well studied using electron microscopy of whole cells and their ultrathin 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 there is protoplasm, consisting of cytoplasm with inclusions and a hereditary apparatus - an analogue of the nucleus, called the nucleoid (Fig. 2.2). There are additional structures: capsule, microcapsule, mucus, flagella, pili. Some bacteria are not favorable conditions capable of forming spores.

Rice. 2.2. Structure of a bacterial cell: 1 - capsule; 2 - cell wall; 3 - cytoplasmic membrane; 4 - mesosomes; 5 - nucleoid; 6 - plasmid; 7 - ribosomes; 8 - inclusions; 9 - flagellum; 10 - pili (villi)

Cell wall- a strong, elastic structure that gives the bacterium a certain shape and, together with the underlying cytoplasmic membrane, restrains 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. 2.3). 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.

The basis of the bacterial cell wall is peptidoglycan. Peptidoglycan is a polymer. It is represented by parallel polysaccharide glycan chains consisting of repeating N-acetylglucosamine and N-acetylmuramic acid residues connected by a glycosidic bond. This bond is broken by lysozyme, which is an acetylmuramidase.

A tetrapeptide is attached to N-acetylmuramic acid by covalent bonds. The tetrapeptide consists of L-alanine, which is linked to N-acetylmuramic acid; D-glutamine, which in gram-positive bacteria is combined with L-lysine, and in gram-tri-

Rice. 2.3. Scheme of the architecture of the bacterial cell wall

beneficial bacteria - with diaminopimelic acid (DAP), which is a precursor of lysine in the process of bacterial biosynthesis of amino acids and is a unique compound present only in bacteria; The 4th amino acid is D-alanine (Fig. 2.4).

The cell wall of gram-positive bacteria contains a large number of polysaccharides, lipids and proteins. The main component of the cell wall of these bacteria is multilayer peptidoglycan (murein, mucopeptide), accounting for 40-90% of the mass of the cell wall. Tetrapeptides of different layers of peptidoglycan in gram-positive bacteria are connected to each other by polypeptide chains of 5 glycine residues (pentaglycine), which gives the peptidoglycan a rigid geometric structure (Fig. 2.4, b). Covalently linked to the peptidoglycan of the cell wall of gram-positive bacteria teichoic acids(from Greek tekhos- 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, with cross-links of peptides.

Rice. 2.4. Structure of peptidoglycan: a - gram-negative bacteria; b - gram-positive bacteria

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 they become red. This is due to the structural features of the cell wall. Peptidoglycan in the cell wall of gram-negative bacteria is represented by 1-2 layers. The tetrapeptides of the layers are connected to each other by a direct peptide bond between the amino group of DAP of one tetrapeptide and the carboxyl group of D-alanine of the tetrapeptide of another layer (Fig. 2.4, a). Outside the peptidoglycan there is a layer lipoprotein, connected to peptidoglycan through DAP. Followed by outer membrane cell wall.

Outer membrane is a mosaic structure composed of lipopolysaccharides (LPS), phospholipids and proteins. Its inner layer is represented by phospholipids, and the outer layer contains LPS (Fig. 2.5). Thus, the outer mem-

Rice. 2.5. Lipopolysaccharide structure

the brane is asymmetric. The outer membrane LPS consists of three fragments:

Lipid A has a conservative structure, almost the same in gram-negative bacteria. Lipid A consists of phosphorylated glucosamine disaccharide units to which long chains of fatty acids are attached (see Fig. 2.5);

Core, or core, crustal part (from lat. core- core), relatively conservative 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 LPS toxicity 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 ketodeoxyoctonic acid. O-specific polysaccharide chain extending from the core of the LPS molecule,

consisting of repeating oligosaccharide units, determines the serogroup, serovar (a type of bacteria detected using 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, as a result, the appearance of rough colonies of R-forms that lose O-antigen specificity.

Not all gram-negative bacteria have a complete O-specific polysaccharide chain, consisting of repeating oligosaccharide units. In particular, bacteria of the genus Neisseria have a short glycolipid called lipooligosaccharide (LOS). It is comparable to the R form, which has lost O-antigen specificity, observed in mutant rough strains E. coli. The structure of VOC resembles the structure of the glycosphingolipid of the human cytoplasmic membrane, so VOC mimics the microbe, allowing it to evade the host's immune response.

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

Between the outer and cytoplasmic membrane is periplasmic space, or periplasm containing enzymes (proteases, lipases, phosphatases, nucleases, β-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 an altered (often spherical) shape are formed: protoplasts- bacteria completely lacking a cell wall; spheroplasts- bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, i.e. acquire a full-fledged cell wall and restore its original shape.

Bacteria of the spheroid 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-shapes(from the name of the D. Lister Institute, where they first

have been 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 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, 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. Unlike eukaryotic cells, the cytoplasmic membrane of a bacterial cell lacks sterols (with the exception of mycoplasmas).

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 cytoplasm of bacteria and is involved in the regulation of osmotic pressure, transport of substances and energy metabolism of the cell (due to enzymes of the electron transport chain, adenosine triphosphatase - ATPase, etc.). With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complexly 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, sporulation, i.e. in processes with high energy consumption. Cytoplasm occupies the main volume of bacteria

cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes, responsible for the synthesis (translation) of proteins.

Ribosomes bacteria have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to the 80S 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. rRNA is a conserved element of bacteria (“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, β-hydroxybutyric acid and polyphosphates (volutin). They accumulate when there is excess nutrients in the environment and act as reserve substances for nutrition and energy needs.

Volyutin has an affinity for basic dyes and is easily detected using special staining methods (for example, according to 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. The metachromatic coloration of volutin is associated with a high content of polymerized inorganic polyphosphate. Under electron microscopy, they look like electron-dense granules 0.1-1 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, tightly packed like a ball. The nucleoid of bacteria, unlike eukaryotes, does not have a nuclear envelope, nucleolus and basic proteins (histones). Most bacteria contain one chromosome, represented by a DNA molecule closed in a ring. But some bacteria have two ring-shaped chromosomes (V. cholerae) and linear chromosomes (see section 5.1.1). The nucleoid is revealed in a light microscope after staining with DNA-specific stains

methods: according to Feulgen or according to Romanovsky-Giemsa. In electron diffraction patterns of ultrathin sections of bacteria, the nucleoid appears as light zones with fibrillar, thread-like structures of DNA bound in certain areas to the cytoplasmic membrane or mesosome involved in chromosome replication.

In addition to the nucleoid, the bacterial cell contains extrachromosomal heredity factors - plasmids (see section 5.1.2), which are covalently closed rings of DNA.

Capsule, microcapsule, mucus.Capsule - a mucous structure more than 0.2 microns thick, firmly associated with the bacterial cell wall and having clearly defined external boundaries. The capsule is visible in imprint smears from pathological material. In pure bacterial cultures, the capsule is formed less frequently. 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 of 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. The capsule is antigenic: antibodies to the capsule cause its enlargement (capsule swelling reaction).

Many bacteria form microcapsule- mucus formation thickness less than 0.2 microns, detected only by electron microscopy.

It should be distinguished from a capsule slime - 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 glycocalyx.

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 that take on

They originate from the cytoplasmic membrane and are longer than the cell itself. The thickness of the flagella is 12-20 nm, length 3-15 µm. They consist of three parts: a spiral filament, a hook and a basal body containing a rod with special discs (one pair of discs in gram-positive bacteria and two 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 are made of a protein called flagellin. (flagellum- flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are twisted in a spiral.

The number of flagella in different species of bacteria varies from one (monotrichus) in Vibrio cholerae to tens and hundreds extending along the perimeter of the bacterium (peritrichus), in Escherichia coli, Proteus, etc. Lophotrichs 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 special methods, based on etching and adsorption of various substances, leading to an increase in the thickness of the flagella (for example, after silvering).

Villi, or pili (fimbriae)- thread-like formations, thinner and shorter (3-10 nm * 0.3-10 µm) than flagella. The pili extend from the cell surface and are composed of the protein pilin. Several types of pili are known. General type pili are responsible for attachment to the substrate, nutrition, and water-salt metabolism. They are numerous - several hundred per cell. Sex pili (1-3 per cell) create contact between cells, transferring genetic information between them by conjugation (see Chapter 5). Of particular interest are type IV pili, in which the ends are hydrophobic, as a result of which they curl; these pili are also called curls. Location

They are located at the poles of the cell. These pili are found in pathogenic bacteria. They have antigenic properties, bring bacteria into contact with the host cell, and participate in the formation of biofilm (see Chapter 3). Many pili are receptors for bacteriophages.

Disputes - a peculiar form of resting bacteria with a gram-positive type of cell wall structure. Spore-forming bacteria of the genus Bacillus, in which the size of the spore 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(from 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 or spherical, the 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).

The process of sporulation (sporulation) goes through a number of stages, during which part of the cytoplasm and chromosome of the bacterial vegetative cell are separated, surrounded by an ingrowing cytoplasmic membrane - a prospore is formed.

The prospore protoplast contains a nucleoid, a protein synthesizing system, and an energy production system based on glycolysis. Cytochromes are absent even in aerobes. Does not contain ATP, energy for germination is stored in the form of 3-glycerol phosphate.

The prospore is surrounded by two cytoplasmic membranes. The layer surrounding the inner membrane of the spore is called wall of spores, it consists of peptidoglycan and is the main source of cell wall during spore germination.

Between the outer membrane and the spore wall, a thick layer is formed consisting of peptidoglycan, which has many cross-links - cortex.

Located outside the outer cytoplasmic membrane spore shell, consisting of keratin-like proteins, co-

holding multiple intramolecular disulfide bonds. This shell provides resistance to chemical agents. The spores of some bacteria have an additional covering - exosporium lipoprotein nature. In this way, a multilayer, poorly permeable shell is formed.

Sporulation is accompanied by intensive consumption by the prospore and then by the developing spore shell of dipicolinic acid and calcium ions. The spore 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: activation, 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 destruction of the shell and emergence of the seedling.

Table of contents of the topic "Anatomy of a bacterial cell. Physiology of bacteria.":
1. Anatomy of a bacterial cell. Surface structures of bacteria. Bacteria capsule. Organization of capsules. Staining of bacterial capsules. Composition of capsules. Antigenic properties of capsules.
2. Bacterial flagella. Location of flagella. Peritrichous. Monotrichs. Polytrichs. Lophotrichs. Amphitrichy. The phenomenon of swarming. Diagnostics of bacterial motility.

4. Cell wall of bacteria. Functions of the cell wall. The structure of the bacterial cell wall. Peptidoglycan. Murein sac. Structure of peptidoglycan (murein)
5. Gram-negative bacteria. Cell wall of gram-negative bacteria. The structure of the cell wall of gram-negative bacteria.
6. Gram-positive bacteria. Cell wall of gram-positive bacteria. The structure of the cell wall of gram-positive bacteria. Bacterial autolysins. Spheroplasts. Protoplasts.
7. Cytoplasmic membrane (CPM) of bacteria. Composition of the cytoplasmic membrane of bacteria. Transport systems. Mesosomes. Periplasmic space.
8. Cytoplasm of bacteria. Bacterial genome. Bacterial ribosomes. Spare bacterial granules.
9. Physiology of bacteria. Nutrition of bacteria. Type of nutrition of bacteria. Holozoans. Holophytes. Water. The importance of water for bacteria.
10. Compounds assimilated by the bacterial cell. Pathways for substances to enter the bacterial cell. Passive transfer. Diffusion.

Besides flagella, surface many bacteria covered with cytoplasmic projections - microvilli. Typically these are hairs (from 10 to several thousand in number) 3-25 nm thick and up to 12 microns long. Microvilli found in both motile and immobile bacteria. These outgrowths help increase the surface area of ​​the bacterial cell, which gives it additional advantages in utilizing nutrients from environment. Specialized microvilli are known - fimbriae And drank.

Fimbriae of bacteria[from lat. fimbria, fringe]. Many Gram-negative bacteria have long, thin microvilli that penetrate the cell wall. The proteins that form them form a helical thread. Main fimbriae function- attachment of bacteria to substrates (for example, to the surface of mucous membranes), which makes them an important factor in colonization and pathogenicity.

F-pili bacteria[from English fertility, fertility, + lat. pilus, hair], or " sex drinking", - rigid cylindrical formations involved in the conjugation of bacteria. Pili were first discovered in Escherichia coli K12, that is, in strains containing F-factor(See the topic “Plasmids”). Usually the cell is equipped with 1-2 pili, which look like hollow protein tubes 0.5-10 µm long; They often have a spherical thickening at the end. Majority F-pills forms a specific protein - pilin. The formation of pili is encoded by plasmids. They are identified using donor-specific bacteriophages that adsorb on pili and lyse cells.

Bacterial cell wall

Most bacteria cell wall consists of a cell wall and the CPM located underneath it. With some convention, the cell membrane can be called the living skin of bacteria, as opposed to the dead substance of the capsule. Cell membrane can be compared to the thin and elastic, but at the same time durable, tire of a soccer ball. Just as a well-inflated football bladder gives elasticity to a ball, so the internal (turgor) pressure of the cytoplasm, which can reach 30 atm in gram-positive bacteria, gives additional elasticity to the cell wall of bacteria. Some bacteria additionally have an outer membrane as the outer layer of the cell wall - glycocalyx.

Glycocalyx[from Greek gfykys, sweet, + kalyx, shell] is formed by the interweaving of polysaccharide fibers (dextrans and levans). It is not detected when grown on artificial nutrient media. The main function of glycocalyx a is adhesion to various substrates. For example, thanks to the glycocalyx, Streptococcus mutatis is able to firmly attach to tooth enamel.