BACTERIA

From Big Medical Encyclopedia

BACTERIA (grech, bakterion stick) — various on biol, to properties group eurysynusic on Earth microscopic, generally one-celled, the organisms belonging to the lowest life forms.

The first data on B. were received in 17 century from researches of Levenguk who found their main forms. B. can exist in the most various conditions.

The majority them is deprived of a chlorophyll. The exception is made by the anaerobic purple and green sulfur bacteria, and also not sulfuric purple B. containing a chlorophyll and using solar energy for photosynthesis. B. can acquire inorganic carbon and nitrogen, to use many inorganic and organic compounds as energy sources, to carry out transformations of carbon, nitrogen, sulfur, iron and other elements.

Along with B.'s seaweed are one of the most ancient organisms on Earth. The cellular texture of B. is similar to blue-green seaweed, actinomycetes (see) and spirochetes (see), with to-rymi as believe, B. are connected phylogenetic. Among B. are reckoned, defiant diseases at the person, animal and higher plants.

A systematics

the First attempts to classify B. by morphological features were made in 18 century. Later physiological characters were the basis for classification. As taxonomical signs the stablest were applied — a form, coloring on Tpainy (see. Grama method ), sporogenesis, type of breath, biochemical, antigenic and other properties, however to a crust, time is not created the classification constructed on the principle of phylogenetic relationship of B. taking into account evolutionary bonds.

Berdzhi's classification was widely adopted (D. Bergey, 1957), the international rules of the nomenclature B are the basis a cut. The nomenclature is sustained in the binomial system accepted in zoological and botanical classifications (see tab. 1). As taxonomical signs properties B are taken various biol.

Table 1



1 mycoplasmas given in the tab. — the smallest educations delimited instead of a rigid cell wall only by a cytoplasmic membrane, significantly different from bacteria are allocated in a separate class now — Mollicutes (see Mycoplasmataceae).

Morphology

Fig. 1. Main forms of bacteria (diagrammatic representation); 1 — 6 — spherical shapes: 1 — staphylococcus; 2 and 3 — diplococcuses; 4 — streptococci; 5 — tetracocci; 6 — sartsina; 7 — 9 — different types of sticks; 10-12 — spiral-shaped forms: 10 — vibrioes; 11 and 12 — a sperilla.

There are three main forms B. — spherical, rhabdoid and spiral-shaped (fig. 1); the big group of filamentous B. combines preferential water B. and does not contain pathogenic types.

Spherical B. — cocci, are subdivided depending on an arrangement of cells after division into several groups: 1) diplococcuses (share in one plane and are located with couples); 2) streptococci (share in one plane, but at division do not separate from each other and form chains); 3) tetracocci (share in two mutually perpendicular planes, forming groups on four individuals); 4) sartsina (share in three mutually perpendicular planes, forming groups of a cubic form); 5) staphylococcus (share in several planes without a certain system, forming the accumulations reminding bunches). The average size of cocci is 0,5 — 1 microns (see. Cocci ).

Fig. 2. An arrangement a dispute (the brightened-up sites) at some species of bacteria: 1 — you. anthracis; 2 — Cl. sporogenes; 3 — Cl. tetani.
Fig. 1. Disputes you. cereus (coloring across Ozheshka)
Fig. 2. Disputes of Cl. tetani (coloring across Ozheshka)
Fig. 3. Sticks of a star-shaped form (bacteroids).

Rhabdoid B. have strictly cylindrical or ovoidny form, the ends of sticks can be equal, rounded off, pointed. Sticks can be located in pairs in the form of chains, but the majority of views is arranged without. certain system. Length of sticks varies from 1 to 8 microns, average to dia. 0,5 — 2 microns. It is accepted to call actually bacteria the sticks which are not forming a dispute (see. Disputes ). The B., forming disputes, are called bacilli. According to the accepted nomenclature carry aerobic forms to bacilli. Anaerobic spore-forming B. carry to clostridiums. Sporogenesis at bacilli and clostridiums is not connected with process of reproduction. Disputes at them belong to type of the endospores representing the round or oval bodies refracting light and which are painted by special methods (tsvetn. fig. 1 and 2). An arrangement a dispute in a cell, their size and a form are characteristic of each type of B. (fig. 2). Nek-ry sticks (mycobacteria, korinebakteriya) are formed by threadlike individuals, others (klubenkovy B.) form branched, star-shaped forms — so-called bacteroids (fig. 3).

Spiral-shaped forms B. subdivide into vibrioes and a sperilla. Curvature of bodies of vibrioes does not exceed one quarter of a turn of a spiral. Spirilla form bends of one or several turns (see. Vibrioes , Spirilla ).

Nek-ry B. have mobility that clearly is visible at observation by method hanging drop (see) or other methods. Mobile B. actively move by means of special organellas — flagellums (see. Flagellums bacterial ) or due to the sliding movements (myxobacterium).

Fig. 4. Capsules of sticks of a scleroma.
Fig. 3. The Klebsiella pneumoniae capsules (coloring across Burri)

Capsule is available for a row B. and is their external structural component (fig. 4 and tsvetn. fig. 3). At a row B. similar to the capsule education in the form of thin slime layer on a surface of a cell is had. At nek-ry B. the capsule forms depending on conditions of their existence. One B. form capsules only in a macroorganism, others — both in an organism, and out of it, in particular on the mediums containing the increased concentration of carbohydrates. Nek-ry B. form capsules irrespective of living conditions (see. Capsular bacteria). The polymerized polysaccharides consisting of pentoses and aminosugars, uronic acids, polypeptides and proteins are a part of the capsule of most of B. The capsule is not amorphous education, and is definitely structured. At nek-ry B., napr, pneumococci, the capsule defines their virulence, and also nek-ry antigenic properties of a bacterial cell.

Cell wall B. defines their form and provides preservation of internal contents of a cell. On features of chemical structure and structure of a cell wall of B. differentiate by means of coloring across Gram.

A structure of a cell wall variously at gram-positive and gram-negative B. The main layer of a cell wall characteristic of all types of B., the rigid layer is (a synonym: mukopeptidny layer, murein, peptidoglikan; the last name most corresponds to a chemical structure of a layer), to-rogo enter the repeating remains of aminosugars into structure — N-atsetilglyukozamina and N-atsetilmuramovoy to - you, forming a basis of linear polymer — murein.

Fig. 5. Diagrammatic representation of a peptidoglikan: chains (slanting lines) are made of N-atsetilglyukozamina (G) and N-atse-tilmuramovoy to - you are (M). Vertically located points — peptide subunits, horizontally located points — the crossing peptide bridges connecting chains in uniform structure of a peptidoglikan.

To the rest of N-atsetilmuramovoy to - you are connected the polypeptide consisting at B.'s most of four amino-acid remains — L - alani - on, D-glutaminic to - you, a L-lysine or diaminopimelic to - you are (DAP) and D-alanine in a molar ratio 1: 1: 1: 1. As a part of peptide depending on B.'s type variations can be observed. The lysine or DAP can be replaced with ornithine, 2,6-diaminobutarovy to - that, etc. Sometimes to the rest glutaminic to - you are attached additional amino acid. Peptide chains are connected with each other to the help of cross polypeptide chains, the structure to-rykh widely varies at different types B. Cross bonds, napr, at staphylococcus, are formed by the pentaglycine bridges connecting D-alanine of one peptide unit to a lysine another. At nek-ry B. cross bonds are identical to peptide units. At E. coli peptide chains are connected directly with each other through D-alanine of one chain and DAP another. The diagrammatic representation of a peptidoglikan is submitted in fig. 5.

Gram-positive B. in addition to a peptidoglikan have teykhoyevy acids (ribit-teykhoyevy and glycerin-teykhoyevye) which are also forming polymer and covalently connected with peptidoglikany. Acids are found in nek-ry B. teykhuronovy and 2-aminomannurovy.

Lipoprotein and lipopolisakharidny layers enter into structure of cell walls of gram-negative B., except a rigid layer. The Lipopolisakharidny layer (L of PS) is most studied at enterobakteriya, and especially salmonellas. The l of PS represents a complex phosphorylation of the heteropolysaccharides covalently connected with the lipid containing a glycosamine (a lipid And). O-antigen of a cell is a part of L of PS (at enterobakteriya). Polisakharidny part L of PS consists of the main (basic) structure and the O-antigenic part. In structure of a basic part inherent in all enterobakteriya, enter heptose, 2-keto-Z-dezoksioktonat (KDO), glucose, a galactose and a N-acetyl-glycosamine. Through KDO a basic part is attached to the component consisting of a lipid And, ethanol of amine, phosphate and KDO. On the other side of (outside) the side chains formed by the repeating oligosakharidny units are attached to basic structure. Outside polisakharidny chains are species-specific and are somatic O-antigens. O-specificity is defined by carbohydrate structure of all side chain, the sequence of an arrangement in it of carbohydrates and trailer sugar, 6-dezoksi-or 3,6-didezoksigeksozy. Inherited disorders in biosynthesis of LPS of enterobakteriya of a basic part or O-side chains lead to emergence of R-forms of mutants (see. Dissociation of bacteria ).

Fig. 6. Cell structure of an enterobakteriya (diagrammatic representation): 1 — determinant groups of O-antigen; 2 — a lipoprotein layer; 3 — a flagellum (N-antigen); 4 — a cytoplasmic membrane; 5 and — ribosomes in cytoplasm; 7 — nucleoid; 8 — the capsule; 9 — a lipopolisakharidny layer; 10 — a rigid layer of a cell wall.

Lipoprotein layer (LP) at gram-negative B., on Weidel representation, is a periblast of a cell wall. LPS is intermediate, the rigid layer is the most deeply located. This scheme does not explain detection of O-antigen without preliminary destruction of L P. Therefore other schemes of a structure of a wall were offered, according to the Crimea LP covers a bacterial cell not with a continuous layer, and through it there passes LPS in the form of «shoots» as it is shown in fig. 6. This representation is confirmed with immunochemical methods with use of ferritin during the studying of localization of O-antigen.

Nek-ry gram-positive B. have a cell wall as well as at gram-negative, consists not only of a rigid layer, but has a multilayer structure. E.g., at streptococci the proteinaceous layer, an intermediate lipopolisakharidny and inner rigid layer is its part. The cell wall is not inert structure in the enzymatic relation. In its structure autolytic enzymes, phosphatase, an adenozintrifosfataza are found.

Cytoplasmic membrane B. adjoins to an inner surface of a cell wall, separates it from cytoplasm and is very important component of a cell in the functional relation. In a membrane oxidation-reduction enzymes are localized, such major functions of a cell as division, biosynthesis of a number of components, chemo - and photosynthesis, etc. are connected with system of membranes. Thickness of a membrane at B.'s most makes 7 — 10 nanometers. By the Elektronnomikroskopichesky method it is revealed that it consists of three layers: two electronic and dense and intermediate — electronic and transparent. Proteins, phospholipids, lipoproteins, a small amount of carbohydrates and nek-ry other connections are a part of a membrane. Many proteins of a membrane of B. are the enzymes participating in processes of breath, and also in biosynthesis of components of a cell wall and the capsule. As a part of a membrane also the permeaza providing transfer in a cell of soluble substances are defined. The membrane serves as an osmotic barrier, it has selective semi-permeability and is responsible for receipt in a cell of nutrients and escaping it products of exchange.

Fig. 7. You. subtilis: 1 — nucleoid; 2 and 5 — a cell wall; 3 — a cytoplasmic membrane; 4 — mesosom; 6 — a cellular partition (ultrathin section, the diffraction pattern; h190 000).

In addition to a cytoplasmic membrane, in B.'s cell is available system of inner membranes, received the name a mesocatfish, to-rye are probably derivatives of a cytoplasmic membrane; their structure varies at different types B. Naiboley mesosom at gram-positive by B. Stroyeniye of mesosom not the same are developed, their polymorphism is noted even at the same look B. Internal membrane structures can be presented by simple invaginations of a cytoplasmic membrane, educations in the form of bubbles or loops (is more often at gram-negative B.), in the form of vacuolar, lammelyarny, tubular educations. Mesosom are most often localized at a cellular partition (fig. 7), also their communication with nucleoid is noted. As in mesosom enzymes of breath and oxidizing phosphorylation are found, many authors consider them analogs of mitochondrions of cells of the highest. It is supposed that mesocatfishes take part in cell division, distribution of daughter chromosomes in the divided cells and sporogenesis. Also functions of nitrogen fixation, chemo - and photosynthesis are connected with the membrane device of a cell. Therefore, it is possible to believe that cell membranes play a certain sort the coordinating role in the space organization of a row of fermental systems and organellas of a cell.

Fig. 4. Grains of volutin at korinebakteriya
Fig. 5. Grains of volutin at korinebakteriya
Fig. 6. Inclusions at Bac. megaterium

Cytoplasm and inclusions. Internal contents of a cell consist from cytoplasms (see), representing complex mixture of various organic compounds which are in colloidal state. On ultrathin sections of cytoplasm (fig. 7) a large amount of grains, a considerable part is revealed to-rykh is ribosomes. Cytoplasm B. can contain intracellular inclusions (tsvetn. fig. 4 — 6) in the form of granules of a glycogen, starch, fatty substances. A row B. in cytoplasm has granules of volutin consisting of the inorganic polyphosphates, metaphosphates and connections close to nucleic acids. The role of volutin is up to the end not clear. Nek-ry authors on the basis of its disappearance at starvation of cells consider volutin as reserve nutrients. Volutin has affinity to the main dyes, shows a hromofilnost and a metachromasia, easily comes to light in cells in the form of large granules, especially at special methods of coloring.

Fig. 8. Polysom — dark accumulations (diffraction pattern).

Ribosomes B. are the place of protein synthesis of a cell, in process to-rogo the structures consisting of a large number of ribosomes (to 20), called by polyribosomes are formed or are more often polysom (fig. 8). The policy takes part in education m-RNK. Upon termination of synthesis of this protein polysom break up to single ribosomes again, or subunits. Ribosomes can freely be located in cytoplasm, but their considerable part is connected with cell membranes. On ultrathin sections of most of B. of a ribosome are found in cytoplasm in the form of granules to dia. apprx. 20 nanometers. The ribosomes of E. coli cleared in the presence of ions of magnesium are besieged during the ultracentrifuging with a speed of sedimentation of 70 S. At more low concentrations of magnesium they dissociate on two subunits with sedimentation constants 50 S and 30 S. Believe that 50 S particle has spherical, and 30 S — the flattened form. During the strengthening of ions of magnesium 70 S of a particle form dimeasures. In a stand-at-ease (out of synthesis of protein) ribosomes are in the dissociated state in ribosomal fraction of cells. Dissociation of ribosomes on subunits is stimulated by a special factor of dissociation. 50 S and 30 S subunits have a pier. weight 1,8 · 106 and 0,85-106 respectively. Both particles consist of ribosomalny RNA (or r-RNA) and a squirrel. 50 S particle contains on one molecule 23 S and 5 S r-RNA. 30 S particle contains one molecule 16 S r-RNA. The proteinaceous structure of ribosomes is heterogeneous. 30 S particles consist of twenty one, and 50 S of thirty — thirty five various proteins. A part of proteins 30 S of particles of ribosomes is necessary both for assembly of ribosomes, and for their functioning, other part is important only in the functional relation. Ribosomalny RNA is important for the correct assembly and the organization of ribosomes.

Extent of aggregation of ribosomes is regulated by ions of magnesium. Polyamines and the ribonuclease I participating are found in ribosomes as believe, in hydrolysis m-RNK.

Fig. 9. Nucleoids you. cereus — dark accumulations in cells (coloring across Romanovsky — to Gimza).
Fig. 10. Radio autography of a chromosome of B. of coli. The tsirkulyarnozamknuty structure is visible; at the left above — the scheme of replication: X \the initial point of replication, Y — an apical point; And — the otrepletsirovanny site; B — the neotrepletsirovanny site; In — a replicative point.

Kernel. Bacteria possess the discrete nuclear structure, in connection with an originality of a structure which received the name of a nukleiid (fig. 9). Nucleoids B. contain the main amount of DNA of a cell. They are painted by Feylgen's method (see. Deoxyribonucleic acid ), are well visible during the coloring across Romanovsky — to Gimza (see Romanovsky — Gimza a method), after acid hydrolysis or in a live state at phase-contrast microscopy, and also on ultrathin sections in a supermicroscope (fig. 7 and 9). Nucleoid is defined in the form of compact single or double education. At the growing cultures nucleoids often look in the form of the doubled educations that reflects their division. Mitotic division of nuclear structures at B. is not revealed. The form of nucleoids and their distribution in a cell are very changeable and depend on a variety of reasons, including and on age of culture. In electronic microphotos in the locations of nucleoids light sites of smaller optical density are visible. The nuclear vacuole is not separated from cytoplasm by a nuclear envelope. The form of a vacuole is not constant. Nuclear sites are filled with bunches of the fine ends forming a difficult interlacing. As a part of nuclear structures of B. are not found histones (see); assume that their role at B. is carried out by polyamines. B.'s kernels are not similar to kernels of other organisms. It formed a basis for B.'s allocation in group of prokariot, unlike the eukaryotes possessing the kernel containing chromosomes, a cover and sharing way of a mitosis. Nucleoid B. is connected to mezosomy. The nature of communication is not known yet. The chromosome of bacteria has tsirkulyarno the closed structure. It was shown by method of radio autography at E. coli (fig. 10), previously marked 3H-thymidine. About structure of DNA judged by distribution of grains of marked thymidine. It is counted that length of DNA of a cell closed in a ring makes 1100 — 1400 microns, and a pier. weight 2,8 · 109 [J. Cairns, 1963].

Fig. 11. Character of an arrangement of flagellums at bacteria; above — peritry; 1 — monotrikh, 2 — amfitry, 3 — lofotry.

Flagellums and fibers. On nek-ry B.' surface there are organellas of the movement — flagellums (fig. 11). They can be found by means of special methods of coloring, a mikroskopirovaniye in a dark field or in a supermicroscope. Flagellums have the spiral-shaped form, and the step of a spiral is specific to each look B. On the basis of quantity of flagellums and their arrangement on a surface of a cell distinguish the following groups of mobile microbes: monotrikh, amfitrikh, lophotrichy and peritrikh. Monotrikh have one flagellum located on one of poles of a cell less often subpolyarno or lateralno. At amfitrikh on each pole of a cell about one flagellum is located. A lophotrichy has a bunch of flagellums on one or two poles of a cell. At peritrikh flagellums are distributed without a certain order on all body of a cell.

M. A. Peshkov (1966) offers several other terminology. Amfi-and a lophotrichy it combines the term «multrikh» and allocates the mixed type having two or more flagellums of a different look in different points of an attachment. The basis of flagellums (blepharoplast) is located in a cytoplasmic membrane. Flagellums almost entirely consist of protein — a flagellin.

Fig. 12. Flagellums and fibers at S. typhi (diffraction pattern).

On nek-ry B.' (enterobakteriya) surface, except flagellums, there are fibers (fimbrias, saw) seen only under a supermicroscope (fig. 12). Distinguish several morphological types of fibers. The first type (general) and the fibers existing only in the presence in a cell of sexual factors is fullestly studied (see. Sexual factor of bacteria ). Fibers of the general type cover all surface of a cell, consist of protein; sexual fibers it is the share 1 — 4 of a cell. Both that and others have antigenic activity (see Conjugation at bacteria).

Physiology

On chemical composition B. do not differ from other organisms.

Fig. 7. Colonies of pigmental micrococci
Fig. 8. Diffusion of a pigment (marsh color) of Pseudomonas aeruginosa in a medium
Fig. 9. Pigmental colonies of Azotobacter chroococcum

Carbon, nitrogen, hydrogen, oxygen, phosphorus, sulfur, calcium, potassium, magnesium, sodium, chlorine and iron are B.'s part. Their contents depends on B.'s type and culture conditions. An obligatory chemical component of cells of B., as well as other organisms, the water representing a universal dispersion medium of living matter is. The main part of water is in a stand-at-ease; its contents variously at different B. also makes 70 — 85% of wet weight to B. Kroma free, there are ionic fraktsrya waters and the water connected with colloid substances. On structure of organic components of a cell of B. are similar to cells of other organisms, differing, however, in existence of nek-ry connections. Proteins, nucleic acids, fats, mono - di - and polysaccharides, aminosugar, etc. are B.'s part. B. have unusual amino acids: diaminopimelic (contained at blue-green seaweed and rickettsiae); N-metillizin which is a part of a flagellin of nek-ry B.; D-isomers of nek-ry amino acids. Content of nucleic acids depends on culture conditions, growth phases, fiziol, and a functional condition of cells. Content of DNA in a cell is more constant, than RNA. The nucleotide composition of DNA is invariable in development of B., is species-specific and is used as one of the major taxonomical signs. Bacterial lipids are various. Fatty acids, phospholipids, wax, steroids occur among them. Nek-ry B. form pigments (tsvetn. fig. 7 — 9) with intensity, widely varies edges at the same look and depends on conditions of cultivation. Solid nutrient mediums are more favorable for formation of pigments. On a chemical structure distinguish carotinoid, hinonovy, melaninovy and other pigments, to-rye can be red, orange, yellow, brown, black, blue or green color. More often pigments are insoluble in mediums and paint only cells. Pigments, water soluble (pyocyanine), diffuse on Wednesday, painting it. Also the backteriochlorophyll giving violet or green coloring a nek-eye photosynthesizing B belongs to B.'s pigments.

Enzymes B. are divided into (endoenzymes) functioning only in a cell and only out of a cell (exoenzymes). Endoenzymes generally catalyze synthetic processes, breath, etc. Exoenzymes catalyze hl. obr. hydrolysis of high-molecular substrates before connection with lower a pier. it is powerful, capable to get in a cell.

In a cell enzymes are connected with the relevant structures and organellas. E.g., autolytic enzymes are connected with a cell wall, oxidation-reduction enzymes — with a cytoplasmic membrane, the enzymes connected with DNA replication — with a membrane or nucleoid.

Activity of enzymes depends on a number of conditions, first of all on temperature of cultivation of B. and pH of the environment. Fall of temperature reversibly reduces, and increase to certain limits (40 — 42 °) increases activity of enzymes. At thermophilic and psychrophile B. the optimum of activity of enzymes matches the optimum temperature of growth. Optimum temperature for mesophilic B., to the Crimea pathogenic B. belong, it is approximately equal 37 °. The optimum of pH generally lies within 4 — 7. Variations of an optimum of pH meet. Enzymes B., activity to-rykh does not depend on presence of substrate in the environment of cultivation, call constitutive. Enzymes, synthesis to-rykh depends on availability of substrate in the environment, are called induced (the old name — adaptive). E.g., formation of a β-galactosidase at colibacillus begins only at addition on Wednesday of lactose, edges are induced by synthesis of this enzyme.

Control of synthesis of enzymes is exercised by inhibition by an end product or way of induction and repression.

Enzymatic activity of B. is used for their identification, most often at the same time sakharolitichesky and proteolytic properties are studied. The Nek-ry enzymes formed by pathogenic B. are factors virulence (see).

Food. B. use nutrients only in the form of rather small molecules getting in a cell. Such way of food characteristic of all organisms of a plant origin, call holophytic. Complex organic matters (protein, polysaccharides, cellulose, etc.) can be the power supply and energy only after their preliminary hydrolysis before simpler connections, water soluble or in lipoida. Ability of various connections to get into cytoplasm of cells depends on permeability of a cytoplasmic membrane and chemical structure of nutrient.

Substances, to-rye are the power supply B., are amazingly various. The major element necessary for live organisms, carbon is. One types B. (autotrophs) can use inorganic carbon from carbonic acid and its salts (see. Autotrophic organisms ), other (heterotrophs) — only from organic compounds (see. Heterotrophic organisms ). The vast majority of B. treats heterotrophs. Digestion of carbon requires a foreign energy source. Not numerous types of B. possessing photosynthetic pigments use energy of a sunlight. These B. are called photosynthesizing. Among them there are autotrophs (green and purple sulfur bacteria) and heterotrophs (not sulfuric purple B.). They are called also respectively photolithotrophs and fotoorganotrofa. Most of B. uses energy of chemical reactions and is called chemosynthetic. Chemosynthetic autotrophs are called hemolitotrofa, and heterotrophs — hemoorganotrofam.

Heterotrophic B. acquire carbon from organic compounds of various chemical nature. The substances containing unsaturated bonds or carbon atoms with partially oxidized valencies are easily acquired. In this regard the most available sources of carbon are sugar, polyatomic alcohol, etc. Nek-ry heterotrophs along with digestion of organic carbon can acquire also inorganic carbon.

B.'s relation to sources of nitrogen also variously. There are B. acquiring mineral and even atmospheric nitrogen. Other B. are incapable to synthesize a proteinaceous molecule or nek-ry amino acids from the simplest compounds of nitrogen. In this group the forms using nitrogen from separate amino acids, from peptones, complex proteic matters and from mineral sources of nitrogen with addition not synthesizable them amino acids are had. To this group B.

Kroma possesses many pathogenic of sources of nitrogen and carbon, B. need phosphorus, sulfur, potassium, magnesium, iron, microelements, and also accessory factors of growth (see. Bacterial growth factors ).

Breath. A part of the substances getting in a bacterial cell, being oxidized, supplies it with necessary energy. This process is called biol, oxidation or breath.

Biological oxidation comes down generally to two processes: to dehydrogenation of substrate with the subsequent electron transfer to a final acceptor and accumulation in biologically available form of the released energy. Oxygen, nek-ry organic and inorganic compounds can serve as final electron sink. At aerobic breath final electron sink is oxygen. Power processes, in to-rykh final electron sink not oxygen, and other connections is, are called anaerobic breath, and nek-ry researchers refer those processes when final electron sink are inorganic compounds (nitrates and sulfates) to actually anaerobic breath.

Understand such power processes as fermentation, in to-rykh organic compounds act at the same time as donors and as electron sinks.

Among B. there are strict aerobes (see), the developing only in the presence of oxygen, strict anaerobes developing only for lack of oxygen and optional anaerobe bacterias (see), capable to development both in aerobic and in anaerobic conditions. B.'s most possesses spatially the organized system of respiratory enzymes which received the name of a respiratory chain or electron transport chain.

Breath at B., like breath of other organisms, is accompanied by processes of oxidizing phosphorylation, is followed by formation of the connections rich with energy-rich bonds (ATP). The energy collecting in these connections is used as required.

As an energy source of B. can use various organic compounds (carbohydrates, nitrogen-containing substances, fats and fatty acids, organic acids, etc.). Ability to receive energy as a result of oxidation of inorganic compounds is inherent only in small group B. The inorganic matters oxidized by them are specific to each type of B. K this B. nitrifying B., sulfur bacteria, iron bacteria, etc. belong. Among them there are both aerobes and anaerobe bacterias.

Photosynthesizing B. turn energy of visible light directly into ATP; this process which is carried out during photosynthesis is called photophosphorylation.

Growth and reproduction

the Bacterial cell begins to share after completion of the consecutive reactions connected with reproduction of its components.

The most important process of growth of a cell is reproduction of its hereditary device. Division of nucleoid is preceded by processes of DNA replication (see. Replication ). Replication begins when the relation of DNA/squirrels of a cell reaches a certain level. Initiation of replication requires synthesis of specific proteinaceous products. On the replicated DNA cells during the studying by an autoradiografichesky method distinguish two points: point of the beginning of replication and apical point (fig. 10). The Replikativny point moves ahead on all DNA of the cell having as it was noted, the structure tsirkulyarno closed. Time of passing of a point of replication from beginning to end of all circular structure of DNA, or time of synthesis of DNA, constantly also does not depend on the growth rate of cells. At quickly growing cultures when time of generation (time proceeding between cell fission) is less, than time necessary for DNA replication (40 — 47 min. at E. coli B/r), new initiation begins before the termination of previous. Thus, quickly growing cultures have several replicative points (forks). Process of DNA replication is followed by a segregation of the synthesized chains of DNA in again formed daughter cells. In division of DNA threads the large role is played by mesosom of a cell.

Growth of rhabdoid cells in cycle time of generation comes down to exponential increase in their length. During division growth of a cell is slowed down and begins after division again.

The end of DNA replication is the moment initiating cell division. Oppression of synthesis of DNA before the end of replication leads to disturbance of process of division: the cell ceases to share and grows in length. On the example of E. coli it is shown that to start division availability of thermolabile protein and such ratio between separate polyamines in a cell is required, at Krom the quantity of a putrestsin shall exceed amount of spermidine. There are data on value of phospholipids and autolysins for process of cell fission.

At growing B.'s culture the full range of ribosomes is synthesized. Ribosomalny RNA is originally synthesized on a DNA matrix, then is modified and turns into mature 16 S and 23 S r-RNA. 5 S r-RNA are also not a direct product transcriptions (see). Predecessors of ribosomes do not contain a full range of ribosomalny proteins. The full range appears only in the course of maturing.

The mechanism of reproduction of mesosom, as well as the membrane device of a cell, is not clear yet. Assume that with a growth of a bacterial cell mesosom are gradually divided.

With a growth of a bacterial cell the cellular partition forms near mezosomy (fig. 7). Formation of a partition leads to cell division. Again formed daughter cells separate from each other. At nek-ry B. formation of a partition does not lead to division of cells: multichamber cells are formed.

A number of mutants at E. coli is received, at to-rykh a cellular partition it is formed or in the unusual place, or along with a partition with usual localization the additional partition close from a pole of a cell forms. As a result of division of such mutants both usual cells, and small cells (mini cells) 0,3 in size — 0,5 microns are formed. Mini cells are deprived, as a rule, by DNA since at division of a parent cell nucleoid does not get to them. Due to the lack of DNA minicells are used in the geneticist B. for studying of expression of function of genes at extra chromosomal factors of heredity and other questions.

At cultivation in liquid mediums the growth rate of population of cells changes in time. Growth of population of B. is divided into several phases. After crops of cells in a fresh medium a nek-swarm B.'s time do not breed — this phase call initial stationary or a log phase. The log phase passes into a phase of positive acceleration. In this phase division B begins. When the growth rate of cells of all population reaches a constant, the logarithmic phase of reproduction begins. During this period it is possible to time generation, quantity of generation and nek-ry other indicators. The logarithmic phase is replaced by a phase of negative acceleration, then there comes the stationary phase. The quantity of viable cells in this phase is constant (M-concentration — max. konts. viable cells). Then the phase of dying off of population follows. Influence the growth rate of population: type of culture of B., age of sown culture, composition of nutrient medium, temperature of cultivation, aeration, etc.

During growth of population of cells in them products of exchange collect, there is an exhaustion of nutrients and other processes leading to transition in stationary and the subsequent phases. At constant addition of nutrients and simultaneous removal of products of exchange it is possible to achieve long stay of cells of population in a logarithmic phase. Most often apply to this purpose hemostat (see).

Despite constant speed of growth of population of B. in a logarithmic phase, separate cells nevertheless are in different stages of division. It is sometimes important to synchronize growth of all cells of population, i.e. to receive synchronous culture. Simple methods of synchronization is change of heating environments or cultivation in the conditions of a lack of nutrients. In the beginning the culture is placed in non-optimal conditions, then replaced their optimum. At the same time at all cells of population the cycle of division is synchronized, but synchronous cell fission happens usually no more than 3 — 4 cycles.

Hypotheses were earlier repeatedly made, according to the Crimea transformation of one forms B. into others in a development cycle goes on a vicious circle. All these hypotheses combine the general term of «cyclogenius». Have theoretical ideas of the cyclogenius in a crust, time only historical interest. However actual data about processes dissociation of bacteria (see) did not lose the value.

Action of external factors

B.'s Viability at action of external factors is studied by different methods, napr, by calculation of the survived cells. For this purpose build the survivorship curves expressing dependence of number of the survived cells on time of influence.

B. are rather steady against low temperatures. B. are more sensitive to action of high temperatures. Usually at B.'s warming up at t ° 60 — 70 ° there is a death of vegetative cells, disputes at the same time do not perish. B.'s sensitivity to high temperatures is used at sterilizations (see).

Different types of B. belong differently to drying. One B. (e.g., gonokokk) very quickly perish, other (mycobacteria) are very steady. However meeting certain conditions (availability of vacuum, special environments), it is possible to receive the dried-up lyophilized B.'s cultures, the long time keeping viability (see. Lyophilizing ).

B. it is possible to destroy by mechanical grinding with various powders (glass, quartz), and also influence of ultrasound.

B. are sensitive to ultraviolet rays; beams with wavelength apprx. 260 nanometers are most effective that corresponds to a maximum of absorption by their nucleic acids. Ultraviolet rays possess mutagen action. X-ray also possesses lethal and mutagen action (see. Mutagens ).

Sensitivity to chemotherapeutic drugs and antibiotics depends on B.'s type and the mechanism of effect of drug on a cell. From sensitive B. stable forms as a result of a mutation can be received or by transfer of factors multiple medicinal stability of microorganisms (see).

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

Pathogenicity and virulence. B. live in the soil, water, a human body and animals. Various groups B. can develop in the conditions not available to other organisms. The qualitative and quantitative structure of B. living in external environment depends on many conditions: pH of the environment, temperature, availability of nutrients, humidity, aeration, presence of other microorganisms (see Antagonism of microbes), etc. The more contains in the environment various organic compounds, the bigger number of B. can be found in it. In uncontaminated soils and waters rather small amount of saprophytic forms B meets. Spore-forming and asporous B., mycobacteria, myxobacteria, coccal forms live in the soil. In water various spore-forming and asporous B. and specific water B. — water vibrioes, filamentous B., etc. meet. At the bottom of reservoirs live in silt various anaerobic B. Among B. living in water and the soil are available nitrogen-fixing, nitrifying, denitrifying, splitting cellulose B., etc. B. growing at high salt contents and supertension live in the seas and oceans, the shining types meet. In contaminated waters and the soil, except soil and water saprophytes, in a large number B. living in a human body and animals — enterobakteriya, clostridiums, etc. meet.

An indicator of fecal pollution usually is availability of colibacillus. Due to the wide spread occurance of B. and an originality of metabolic activity of their many types they are of exclusively great importance in cycle of matter in the nature. Many types of B. participate in a nitrogen cycle — from the types splitting proteinaceous products of plant and animal origin to the types forming nitrates to-rye are acquired by the higher plants. Metabolic activity of B. causes a mineralization of organic carbon and formation of carbonic acid, return a cut in the atmosphere is important for maintenance of life on Earth. Digestion of carbonic acid from the atmosphere is made by green plants thanks to their photosynthetic activity. The big role belongs to B. in a sulfur cycle, phosphorus, iron.

Rather small part of all known microbes is capable to cause diseases of the person and animals. Potential ability of B. to cause infectious diseases, being their species character, is called pathogenesity or pathogenicity. At the same look degree of manifestation of pathogenic properties can vary quite widely. Degree of pathogenicity of a strain of a certain type of B. is called it virulence (see). Among B. there are conditionally pathogenic types, pathogenesity to-rykh the Genetics of bacteria == Genetics of bacteria — the section of the general genetics studying heredity and variability at B depends on a condition of a macroorganism, external environment, etc. ==. Relative simplicity of the organization B., their ability to grow in synthetic environments, proliferation allow to analyze rather seldom arising changes genome (see) B., making multi-billion populations and to track their inheritance. The special methods providing selection from huge population of the separate genetically changed bacterial cells, transfer of a chromosome or its fragments from one cells (donors) to other (recipients) with the subsequent genetic analysis of the arisen recombinants are for this purpose used (see. Recombination ). Methods genetic analysis (see) B. allowed to study not only the organization of a bacterial chromosome, but also to decipher fine structure of a gene, and also to establish functional relationship of genetic units, components separate bacterial operons (see).

Development geneticists B. is connected with studying bacterial transformations (see), a cut gave the chance to establish a role of DNA as a material basis of heredity. During the studying of genetic transformation at B. methods of extraction and purification of DNA, biochemical and biophysical methods of the analysis of its properties were developed. It allowed not only to study genetic changes at the cellular level, but also to compare these changes with structural change of DNA. Thus, in total with genetic methods methods of a biochemical research of genetic material provided a possibility of the analysis of patterns of bacterial genetics at molecular level.

Among B. colibacilli are the most studied in the genetic relation, at to-rykh the ways of transfer of genetic material (a chromosome or its fragments) from the donor to the recipient which are carried out or by direct crossing were open (see. Conjugation at bacteria ), or by means of bacterial viruses (see. Transduction ). Other microorganisms possessing the same types of exchange of genetic material and according to the genetic characteristic approaching colibacilli, are salmonellas.

The consistent patterns of genetic exchange determined on colibacilli and salmonellas are inherent also in some other the microorganisms playing an important role in infectious pathology. Phenomena of conjugation and transduction are found also in shigellas and nek-ry other pathogenic microorganisms that allows to carry out the genetic analysis of the factors causing their pathogenicity.

The microorganisms capable to genetic transformation are of considerable interest to clarification of molecular mechanisms, various genetic phenomena, at a cut of a bacterium recipients absorb the purified DNA extracted from donor bacteria. In experiences of transformation genetic activity of the isolated, extracellular DNA comes to light that allows to analyze functional activity of DNA subjected to various influences changing its structure both in vivo, and in vitro.

Therefore in molecular and genetic researches the transformed B.'s types, such as you are widely used. subtilis, H. influenzae, Pneumococcus, etc.

Properties B., as well as any other organisms, are defined by a set of genes inherent in them. Record of the genetic information coded in bacterial genes is carried out on the basis of a universal triplet code (see. Genetic code ). Yanovsky (S. of Janofsky) obtained the evidence of a collinearity (compliance) between the sequence of nucleotides and the sequence of amino acids in polypeptide and in vivo structure of the separate triplets coding inclusion of various amino acids is established.

Gene pattern, inherent B., defines them genotype (see). B., possessing the same genotype, are not always identical on the properties; their properties can vary depending on the environment of cultivation, age of bacterial cultures, temperature of cultivation and some other environmental factors. The genotype defines properties only potentially inherent in bacterial cells, expression to-rykh depends on functioning (activity) of specific genetic structures. B.'s chromosome includes 2 types of functionally various genetic structures: the structural genes determining specificity of proteins to-rye this cell are capable to be synthesized, and the regulatory genes regulating activity of structural genes depending on environmental conditions, in particular from existence or lack of substrate of synthesizable enzyme or from concentration of connection necessary for a cell, from a condition of genetic material (DNA replication) and so forth.

In an active state structural genes are transcribed (see. Transcription ), i.e. become available to reading of genetic information by means of a DNA-dependent RNA polymerase. The information RNA forming in the course of a transcription (i-RNK) is broadcast in the corresponding polypeptide, the structure to-rogo is coded in these structural genes.

As regulation synthetic systems B. divide into 2 look: catabolic and anabolic. The first carry out utilization to a necessary cell of energy, the second provide biosynthesis of the connections necessary B.

The catabolic E. coli system which is carrying out splitting of lactose on glucose and a galactose is studied by Jacob and Mono in detail (F. Jacob, J. Monod).

Enzymes of this system (a β-galactosidase, a galaktozidpermeaza and a galaktozidtransatsetilaza) are determined by the corresponding structural genes. Near structural genes the regulatory site, the so-called operator who is «including» and who is «switching off» reading of information (transcription) from structural genes is located.

Other regulatory unit of this system is the gene controlling synthesis of a repressor — the squirrel capable to connect to the operator. In the presence of a repressor structural genes are not transcribed by a RNA polymerase and synthesis of the corresponding enzymes does not happen. Between the operator and a regulator gene there is a short site of DNA — promoter — the place of landing of a RNA polymerase. The lactose added B. to the environment of cultivation connects a repressor, the operator is free, and structural genes begin to be transcribed therefore there is a synthesis of enzymes. Thus, the lactose which is substrate of effect of enzymes performs function of the inductor of their synthesis.

Regulation of this sort is inherent also to other catabolic systems. The synthesis of enzymes induced by substrates of their action call indutsibelny.

Other regulation is inherent in anabolic bacterial systems. At these systems the regulator gene controls synthesis of an inactive repressora-aporepressor. At trace amounts of the final metabolite controlled by structural genes of this biochemical way (e.g., some amino acid), the aporepressor does not connect to a gene operator and does not interfere, therefore, with work of structural genes and synthesis of this amino acid. In case of excess formation of an end product the last begins to function as a korepressor. Contacting an aporepressor, the korepressor turns it into the active repressor connecting to a gene operator. As a result transcribing of structural genes and synthesis of the corresponding connections stop, i.e. repression of system is observed. In the course of an expense a cell of an excess final metabolite the active repressor turns into an aporepressor again, the gene operator is released and structural genes gain activity again, i.e. there is derepression of system.

Thus — catabolic (indutsibelny) and anabolic (repressibelny) — regulation as a feed-back is inherent to genetic systems of an oboy sort: accumulation and an expense of an end product regulates its synthesis by anabolic systems; in catabolic systems as the regulator substrate of effect of synthesizable enzymes acts.

Shifts during cellular synthetic processes, owing to-rykh can arise unheritable changes of properties B. of the same genotype, can be expressed in various degree depending on environmental conditions. Sharply violated living conditions can lead to switching off of function of separate structural genes or their hyperfunction that in turn can lead to considerable morphological changes, disharmonic growth and, eventually, to death of cells.

The complex of the properties B. revealed in these living conditions is called a phenotype. B.'s phenotype though depends on the environment, but is controlled by a genotype since character and extent of phenotypical changes, possible for this cell, is defined by gene pattern, i.e. a genotype.

Both structural, and regulatory genes of B. are localized in a bacterial chromosome and in the sum form the genetic device B. In addition, B. can bear extra chromosomal genetic determinants — plasmids (see), to-rye, as a rule, are not vital for a cell. On the contrary, activation of functions nek-ry of them (e.g., bakteriotsinogen) is pernicious for the bacterial cells which are not bearing plasmids. At the same time plasmid elements give to B. a number of the properties which are of considerable interest from the point of view of infectious pathology. So, by plasmid determinants multiple resistance to medicinal substances can be caused (see. R-factor ), production of alpha hemolysin and other bacterial toxins.

B.'s chromosome, as well as cells of the higher organisms, is localized in a kernel.

Unlike cells of the higher organisms, the bacterial kernel is deprived of a cover and is called as nucleoid. The amount of nucleoids in bacterial cells varies depending on a growth phase of culture: number of nucleoids at colibacilli as much as possible in quickly breeding cultures being in a logarithmic growth phase. Colibacilli contain in a stationary growth phase on one nucleoid. B.'s chromosome represents the molecule DNA closed in a ring with a molecular weight about 1,5 — 2 X 109 dalton.

Fig. 13. The scheme of the sequence of transfer of genetic material at conjugation of E. coli illustrating ring structure of a bacterial chromosome. Letters designated various genes. The right arrow — the sequence of transfer of genes (In, D,E,A,B) to the recipient a donorny strain 1; the left arrow — the sequence of transfer of genes (D, In, B, And, E) to the recipient a donorny strain 2.

The ring structure of a bacterial chromosome is established by three methods: autoradiografichesky, elektronnomikroskopichesky and genetic. In the first case autoradiogramma of ring structures of bacterial DNA, in the second — elektronnomikroskopichesky images of the isolated ring DNA are received, in the third — consistent patterns of genetic exchange, explainable are determined only by a ring structure of a chromosome. It can be explained the following conditional example. Let's say that in the course of B.'s (conjugation) crossing from one B. to another the genes designated by letters A, B, B, G, D, E. Odin from the used donorny strains of Hfr (reduction from English expression of high frequency of recombination are transferred — the high frequency of a recombination) has a point of the beginning of transfer of a chromosome in the field of a gene of Century. In this case the following order of transfer of genes is observed: In, D, E, A, B. The second strain of Hfr begins transfer of a chromosome with a gene D and transfers it in the direction opposite to previous. Genes in this case are transferred in the following order: D, In, the B, And, the preservation of the sequence of transfer of genes shown to E. Eksperimentalno at the changed order of their transfer easily is explained by a ring structure of a chromosome (fig. 13).

The methods giving the chance experimentally to carry out transfer of genetic material at B. (conjugation, transduction and transformation), allowed to construct the genetic map of a bacterial chromosome reflecting relative localization of genes. For the purpose of genetic mapping conjugation is widely used, at a cut big sites of a bacterial chromosome, and sometimes and all chromosome of the donor are transferred to the recipient. At pairing mapping apply various approaches: establish transfer of separate genes on time, reveal the linked transfer of genes, establish transmission frequency of the genes which are not subjected to selection (non-selective), located proksimalno and distally concerning the selected gene, etc. Conjugation, however, in most cases does not provide a possibility of rather exact mapping as at the same time recombination (see) it is carried out on rather extended sites of a chromosome. Exact mapping is made by means of transduction at which shorter fragments of a chromosome of a bacterium which are not exceeding 0,01 of its lengths are transferred. One of the main methods of transduktsionny mapping consists in definition of a possibility of a kotransduktion (i.e. joint transfer) the mapped gene and a gene, localization to-rogo in a chromosome is known. Existence of a kotransduktion testifies to the close (linked) arrangement of the analyzed genes. By means of transduction it is possible to establish an order of an arrangement of genes also. For this purpose use a special method of the genetic analysis — the so-called test of three points, at Krom the analysis of crossings is kept concerning three genes.

Transformation for mapping is used rather seldom. Retsipiyentny B.' processing gives to the transforming DNA the chance to transfer only very small sites of a bacterial chromosome. Thereof by means of transformation it is possible to analyze only genes, to-rye make groups of couplings.

The genetic map of E. coli of K-12 constructed on the basis of the long-term genetic researches conducted in various laboratories of the world contains several cells of localized genes in a crust, time.

Fig. 14. The circular genetic map showing an arrangement of genes in a chromosome of E. coli. Genes are designated by the symbols deciphered in tab. 3. Figures on inner surfaces of circles designate the units of length of the card (time, during which this gene is transferred at conjugation) expressed in minutes (from 0 to 90 min.).

In fig. 14 the genetic map of E. coli published in 1970 by A. L. Taylor in the Bacteriological Reviews magazine (USA) is submitted. For convenience of orientation the circle of the genetic map which is schematically representing a chromosome is divided into pieces — the minutes in the sum making time necessary for transfer in the course of conjugation of all chromosome. For colibacilli this time makes apprx. 90 min. The symbols placed on a circle designate the corresponding genes and are deciphered in tab. 3, includes edges apprx. 2000 bacterial genes, functions to-rykh in life activity of a bacterial cell are considerably studied. Data on localization of genes on B.'s chromosome allow to solve specific objectives of practical microbiology. They serve as necessary premises for studying of virulence and B.'s pathogenicity, their medicines resistance, a possibility of creation of attenuirovanny strains and for other purposes. In an arrangement of genes of colibacillus and salmonellas there is an expressed homology.

In some cases genes (cistrons) controlling separate stages of synthesis of a final metabolite are located in one site of a bacterial chromosome. The sequence of an arrangement of genes at the same time corresponds to the sequence of use of the intermediate compounds determined by them during synthesis of a final metabolite. In the same site of a chromosome where structural genes are located, also the regulatory genetic units making in total with the corresponding structural genes can be located operon (see). Example of such operons are groups of the genes providing synthesis of a histidine, tryptophane etc.

In other cases structural and regulatory genes of the same biochemical way are placed in various areas of a bacterial chromosome, the genes controlling synthesis of methionine, splitting of pectine sugar, synthesis of purines, etc. can be an example of what.

Studying of genetic exchange at B. is not limited to the purpose of genetic mapping. The possibility of such exchange is used also during the receiving new strains, useful to the person, B. In particular, the recombination between pathogenic and nonpathogenic B. can be used for designing of attenuirovanny strains, i.e. strains with the weakened virulence, live vaccines, suitable for production. Such strains can be received from pathogenic bacteriums (e.g., from dysenteric B.) at substitution of the genetic area (or areas) defining their pathogenicity, the respective sites of a chromosome of nonpathogenic B. (e.g., colibacilli). For creation of attenuirovanny strains it is necessary not only to provide a possibility of genetic exchange, but also previously to study genetic bases of pathogenicity, virulence, an immunogenicity and to map the genes defining them. Only provided that designing of the full-fledged vaccinal strains which lost only virulence, but kept the properties providing an immunogenicity can be carried out.

Genetic exchange at B. is carried out and under natural conditions their dwellings, the recombinational variability of B. which is shown in formation of atypical forms is a consequence of what. This circumstance gives to studying of recombinational process practical interest since the mechanism of education, pathogenetic and diagnostic value of atypical forms — the topical issues of infectious pathology.

In addition to phenotypical and recombinational variability, B. is inherent mutational variability, i.e. the variability caused by the mutations representing the restructurings of genes, full or their partial loss (deletions) which are not connected with recombinations. B. are widely used for studying of patterns of mutational process. Mutation (see), i.e. change of a genotype — the phenomenon caused by action of mutagenic agents. They are a basis for carrying out all genetic researches since studying of function of genes, their mapping and other genetic tasks can be solved only by means of the corresponding mutants. Character of the bacterial mutants forming under the influence of mutagenic agents does not depend on the mechanism of action of mutagens (see). The idea of adequacy of mutational variability of B. to the used mutagens, i.e. of specific action of the last created at the first stage of development of bacterial genetics, was wrong, just as wrong was a concept about the spontaneous nature of mutational process. The specified representation recognized that at action of the agents causing death of the main part of bacterial population, researchers received the mutations corresponding to the applied agent. So, e.g., effect of streptocides was followed by allocation of sulfamidorezistentny mutants, action of phages — allocation of phagoresistant mutants etc. Luriya's (S. Luria) works, Delbryuka (M. of Delbruck), J. Lederberg and H. Newcombe it was shown that formation of such mutants happens before addition of perniciously acting agent, and the last plays only a role of the selecting factor. Mutational changes in bacterial populations arise in many genes, but the selecting agents select only corresponding mutations. So, e.g., mutating B.'s population can contain different mutants: auxotrophs — incapable to synthesize any connections necessary for a cell; the mutants which lost or gained ability of fermentation of separate carbohydrates; resistant to antibiotics etc. During the seeding of such population on Wednesday with an antibiotic not mutating individuals, just as individuals bearing the mutations which do not have relations to an antibiotikoustoychivost will not give growth. Only B. having mutations in the gene defining the corresponding resistance will grow up on such environment. It, however, does not mean that the origin of antibiotic-resistant mutants is connected with influence of the selecting agent. Origin of resistant mutants, as well as the mutants which remained undetected on the Wednesday with an antibiotic are the mutational events made before influence of the selecting agent. In turn it does not mean that the selecting agent cannot have mutagen activity, but in the presence of that it induces mutations not only in the genes corresponding to the mechanism of its action but also as any other mutagen, in the most various genes, and selects only respectively

the concepts changed B. Nesostoyatelnost about a spontaneous mutirovaniye B. was disproved on the ground that during the testing of numerous chemical connections and physical. agents, perhaps, acting on usually cultivated B.'s populations, it was established that mutagen activity is inherent to extremely wide range of factors, including natural metabolites B. Action of these factors not always gives in to control, but explains an origin of so-called natural mutations.

According to the modern concept, natural mutations represent the phenomenon of the same order, as experimentally received mutations called by induced. Both those, and others, are prichinno caused. Distinctions consist only that the induced mutations arise under the influence of specially applied mutagenic agents, the agents causing natural mutations remain obscure. The term «spontaneous», thus, does not capture the essence of the phenomenon and is applied conditionally to designation of the mutations arising without special influences.

The mutations caused by influence of mutagenic agents result from change of the sequence of nucleotides of DNA, manifestation of what is loss or change of function of the polypeptide coded by this gene or change of properties of regulatory units of a bacterial genome (the operator, promoter). On «extent» distinguish gene and chromosome mutations. The first mention one gene, the second extend more than to one gene. Chromosome mutations result from loss of a large number of nucleotides (deletions). Genovariations more often are dot, i.e. consist in replacement, an insert or loss of one couple of nucleotides of DNA. Distinguish simple and difficult replacements of nitrogen bases in DNA — transitions and transverziya (see. Mutation ).

B. direct and reverse mutations are inherent. The last often have suppressor character. All known mutagens have mutagen effect on bacterial cells. The most often applied mutagens in bacteriological genetic researches are ultraviolet rays, a penetrating radiation, mono - and bifunctional alkylating agents, analogs of the bases and some other.

The researches of the last years conducted on B. opened existence of genetically determined systems providing a reparation of damages of genetic material (DNA). These researches began a recent trend in genetics and molecular biology. The data obtained during the studying of bacterial reparative activity led to review of a number of ideas of mechanisms of action of mutagenic agents, formation, fixing and phenotypical expression of mutational changes.

Antigens of bacteria

Antigens B. are localized in flagellums, the capsule, a cell wall, membranes and other structures of a cell. Antigens B. — biologically active components of a cell defining it immunogene, toxic and invasive properties. Interpretation of chemical structure of bacterial antigens, control of their synthesis by a cell and localizations in it, and also immunogene specificity is a theoretical basis for creation of effective diagnostic methods and specific immunoprevention of bacterial infections.

Distribution of antigens in a bacterial cell is studied immunotsitol. by methods — specific capsular reaction according to J. Tomcsik, a direct and indirect method of fluorescent antibodies, way of antibodies, marked ferritin, iodine, mercury or uranium, using a submicroscopy of ultrathin sections, and also by means of allocation of separate structures for their the subsequent immunol. studying. From bacteria apply stress rupture by means of small glass balls to release of antigens, ultrasound, high pressure, detergents, a lysozyme or a bacteriophage. Soluble antigenic complexes remove from bacteria by their processing by proteolytic enzymes, hot water, trichloroacetic to - that, a diethyl glycol, phenol, urea, pyridine, ethyl ether, etc. Soluble antigens clear gradient ultra-centrifuging by means of column chromatography or a preparative electrophoresis. High cleaning antigens receive from enterobakteriya, pertussoid microbes, streptococci, etc.

Among antigens of bacteria distinguish tipo-, twisted, gruppo-and rodospetsifichesky, and also «nonspecific». The majority tipo-and group-specific antigens is localized in flagellums, the capsule and a cell wall of bacteria. Antigens of membranes and intracellular structures of bacterial cells are studied insufficiently.

Flagellar antigens (N-antigens) represent protein (flagellin) about a pier. weighing 20 000 — 40 000, consisting of alpha and beta and polypeptide chains. At analytical ultracentrifugation flagellin forms one homogeneous peak with coefficient of sedimentation 1,5 — 1,68. During the heating to t ° 100 ° in highly acid or alkaline condition flagellar antigens are inactivated. Assume that the amino-acid structure of different serotypes of flagellar antigens of salmonellas, escherichias and other enterobakteriya is various and it defines their standard specificity. On distinction in specificity of flagellar antigens serodifferentiation of salmonellas is constructed. The isolated flagellums of enterobakteriya, a cholera vibrio and other bacteria react as N-antigen (see Flagellums bacterial), however the fraction of flagellums contains always impurity of O-antigen. Flagellums and flagellin S-and the Proteus mirabilis R-forms contain the general and differing antigenic components. Antigenic specificity depends on connection and the sequence of subunits of a flagellin of flagellar thread. By method immunodiffusions (see) at N-antigen two components come to light. By means of preparative immunochemical methods it is possible to receive the N-antigen purified of O-antigen. The purified N-antigen has no protective activity in experiences on laboratory animals. Soluble flagellar antigens use for preparation of erythrocyte N-diagnosticums.

Capsular antigens (K-antigens) many bacteria of a tipospetsifichna also stimulate specific immunity (see). Many of capsular antigens are polysaccharides or mukopeptida.

Capsular antigens of pneumococci — type-specific polysaccharides, in the isolated look have properties of haptens (see. Haptens ) also are designated as soluble specific substance (SSS). In the capsule of the activator of a malignant anthrax there are a hapten-peptide, and also antigens proteinaceous polisakharidnoy the nature, sensitive to proteolytic enzymes. The capsular glutamilovy polypeptide found in you. megaterium, has properties of antigen, cross reacting with antigens of a cell wall of the same microbe. Capsular antigens of the polisakharidny nature are revealed at microbes of the sort Acetobacter. These antigens cross reacted with antiserums to streptococci of group B and G, and also to pneumococci of the 23rd type. Cross serol, reaction is caused by existence in antigens of the general determinant group — L-rhamnoses.

Cross-reactions between capsular polisakharidny antigens of meningokokk of group A and you are established. pumilus, meningokokkam of group C and E. coli 016: NM, pneumococci like III and E. coli of K7, etc.

In the capsule (more precisely to the microcapsule) enterobakteriya polisakharidny antigens are found: Vi-antigen (see) at S. typhi, S. paratyphi With, E. coli, E. ballerup, B(K) - antigens at escherichias, K-antigens at klebsiyell. Capsular antigens of the proteinaceous nature are found in nek-ry salmonellas, to-rye have protective properties (S. typhimurium, S. adelaide, Citrobacter). Capsular polisakharidny antigens K. pneumoniae have adjuvant effect (see. Adjuvants ).

In a cell wall of many species of microbes twisted and rodospetsifichesky antigens are revealed tipo-, gruppo-. According to Krause's scheme (R. M of Krause, 1963) the cell wall of a streptococcus contains type-specific proteinaceous antigens (M-substance) and group-specific antigens of the polisakharidny nature. M-antigen (there are about 60 types) is protective antigen; in partially cleared look it is offered as a vaccine. Carried out an amer. scientists check of the vaccine consisting of partially purified M-antigen showed that drug caused rheumatism in a part of vaccinated children. According to a number of authors, M-antigen is closely connected with the antigen which is cross reacting with antigen of a cardiac muscle of the person. Assume that cross reacting antigen and M-antigen are different determinants of one proteinaceous molecule. It is revealed also that between M-antigen of a streptococcus of the first type of group A and the HLA system of lymphocytes of the person there is a communication. Other group-specific antigen of a cell wall of streptococci is mukopeptidny antigen, specificity to-rogo also N-atsetilgalaktozaminom is caused N-atsetilglyuko-zaminom (for streptococci of group A) (for streptococci of group C). Group-specific antigen of lactic streptococci is intracellular teykhoyevy to - that.

In a cell wall of stafilokokk species-specific antigens — proteinaceous A-antigen in a surface layer of a wall and teykhoyevy to - that are concentrated, edges in a complex with mukopeptidy are made by the inner layer of a wall. A-antigen — the precipitinogen found in the majority of strains of Staphylococcus aureus, its pier. weight 13 200. It has ability to enter nonspecific reaction with Fc - fragmen - volume of immunoglobulins of a class G of blood serum of the person and nek-ry animals. Teykhoyevy to - that is the specific precipitinogen consisting of subunits of a poliribitolfosfat, amine (determinant group) and D-alanine are attached to Krom N-acetyl of glucose. Teykhoyevy to - that is found in cell walls of streptococci, stafilokokk, micrococci you. subtilis and lactobacilli. It is established that teykhoyevy to - that, isolated from stafilokokk, has protective properties. From cell walls of Cl. botulinum of type A is isolated and cleared the proteinaceous thermostable antigen steady against effect of trypsin.

In cell walls of korinebakteriya, nokardiya, mycobacteria and actinomycetes twisted and rodospetsifichesky antigens are found. The structure of a mukopeptid of a cell wall of korinebakteriya, nokardiya and mycobacteria includes pectine sugar and a galactose, to-rye cause cross serol, reactivity between strains of these groups. In a cell wall of a diphtheritic microbe two antigens are revealed: surface type-specific protein and more deeply located group-specific thermostable polysaccharide. Difficult enrollment of antigens is revealed in a cell wall of anaerobic korinebakteriya by method of a radio immunoelectrophoresis. Acid polysaccharide was the main component of cell walls of these microbes. Group-specific mukopolisakharidny haptens are revealed in cell walls you. anthracis. These haptens react in a precipitation test with the similar antigens isolated from you. cereus. Type-specific antigens you. megaterium are also localized in a cell wall.

About - antigen (endotoxin) of enterobakteriya is localized in a medine of a cell wall and represents the complex connection consisting of protein or peptide, polysaccharide and a lipid. Lipopolisakharid (a glyutsidolipoidny complex) taken by mix of phenol with water has a pier. the weight 106 — 107, for 60 — 70% consists of fosforilirovanny polysaccharide and for 20 — 40% — of a lipid (a lipid And fat to - t). Pier. the weight of the purified polysaccharide is equal to 20 000 — 60 000. Polysaccharide of O-antigens of different types of enterobakteriya is constructed by one principle and consists of the basic structure and side S-specific chains which are determinant groups. The basic structure (differently R-lipopolisakharid) all serotypes of salmonellas includes a glycosamine, 2-keto-Z-dezoksioktanat (KDO), L - glycero - D - semolina heptose, a galactose and glucose.

6 hemotip of R-lipopolisakharidov revealed at the corresponding R-mutants are known (Ra, Rb, Rc, Rd1, Rd2 and Re), to-rye differ on degree of deficiency in chemical structure. 3,6-didezoksigeksoza are a part of proteinaceous chains 6-dezoksi-and especially. S-specific side chains are constructed of the repeating oligosaccharides. O-factors represent a part or all determinant group of O-antigen. They are classified under Kaufermann's scheme — Whyte by means of cross or homologous agglutination tests. The trailer sugar having the greatest affinity with an active center of an antibody is designated as immunodominant sugar. The O-factor 2 (group A) is determined by immunodominant sugar paratozy, the O-factor 4 (group B) — abequose, the O-factor 9 (group D) — tivelozy etc. Immunodominant Shigella dysenteriae sugar is rhamnose. Specificity of the O-antigenic complex is provided not only immunodominant sugar, but also the sequence of an arrangement of sugars in a side chain and the nature of chemical bonds between separate sugars. Originally in a microbic cell the basic structure of polysaccharide, and then side chains is synthesized. A lipidic part of O-antigen (a lipid And) at all enterobakteriya is almost identical. The lipid And represents a long chain fat to - t, derivatives of a polyphospho-d-glycosamine, it is strongly connected with O-specific polysaccharide. At the same time biosynthesis of a molecule of polysaccharide, and also all molecule of O-antigen is genetically determined.

The isolated O-antigen (lipopolisakharid) has branchy structure, edges is broken during the processing of a complex dezoksikholaty sodium; so-called gaptenny subunits, from are formed to-rykh, apparently, all complex is constructed. The isolated O-antigens are toxic, pyrogenous, cause a local and general phenomenon of Shvarttsman (see. Shvarttsmana phenomenon ), a necrosis of tumorous fabric, specific and nonspecific resistance, and also have the immunostimulating and immunodepressive activity. Assume that toxic activity of O-antigens is caused by a lipid And. Administration of O-antigen an animal is followed by a leukopenia and thrombocytopenia. O-antigen causes the phenomenon of tolerance which is followed by noticeable increase in phagocytal activity. In addition to O-antigen, in cell walls of enterobakteriya antigens, and also the general antigens, labile to heating, are found.

In 1962 Mr. of Kunin (S. of Kunin) et al. for the first time described the general antigen of enterobakteriya, to-ry on specificity differs from O-antigen. The general antigen extracted from E. coli 014 — polysaccharide, causes products of specific antibodies in rabbits.

Lipopolisakharid, or a lipid And, entered to an animal together with the general antigen, suppresses products of antibodies to the general antigen. Other type of the general antigen called by Gorzhinsky and Brodkhage (O. O. of Gorzynski, 1964; The Island of O. of Brodhage, 1961, 1962) S-antigen, is found in E. coli and Sh. sonnei. At Sh. sonnei by means of hemagglutination reaction is revealed the bacterial agglutinogen (VA) connected with lipopolisakharidy. In 1969 E. Engelbrecht reported about one general antigen at enterobakteriya — a «alkogolfilny» factor which was received from S. paratyphi And yes In, S. bareilly. It is supposed that «alkogolfilny» antigen — polysaccharide. In cell walls at a cholera vibrio specific alpha antigen, at the causative agent of whooping cough — proteinaceous protective antigen and a gistaminsensibiliziruyushchy factor, at a plague microbe — the antigen extracted by mix phenol — water, and traces of fraction I is localized.

Protective activity of the isolated cell walls is shown in experiences with stafilokokka, streptococci, tulyaremiyny a microbe, the causative agent of plague, enterobakteriya, a pertussoid microbe, mycobacteria, a cholera vibrio, brucellas. Remove the soluble antigens having protective activity from cell walls of the specified microbes. Cell walls of many gram-positive and gram-negative microbes cause in laboratory animals formation of granules, dermatitis, hepatitises, hron, carditises and arthritises. Cell walls stimulate release of lizosomalny enzymes in experiences of in vitro, have cytotoxic effect, inhibit flyutsitoz bacteria and growth of cells.

Thus, superficial structures of many bacteria contain tipo-, gruppo-, twisted and rodospetsifichesky antigens, and also the general antigens for different types of microbes. Many of the listed antigens are important in a pathogeny of diseases and formation of specific immunity.

Antigens of membranes and intracellular structures. In membranes of bacteria specific antigens are concentrated. So, antigens of a cytoplasmic membrane you. megaterium differ on the specificity from antigens of a cell wall.

Studying of an antigenic structure of membranes of Micrococcus lysodeicticus showed that on a surface of a cytoplasmic membrane 8 antigens are located. In fraction of membranes E. coli 0111: To 4: H12 and other enterobakteriya are found About - and N-antigens, and also not identified antigens. It is established that 0 antigen of membranes is identical to O-antigen of cell walls. N-antigen of membranes is identical to N-antigen of the isolated flagellums since a basal part of a flagellum is attached or located on an inner surface of a cytoplasmic membrane. Therefore N-antigenic activity of membranes is caused by antigenic activity of a basal part of a flagellum. The proteins extracted from membranes of mycoplasmas different serol of groups, had specific antigenic activity. From the pertussoid microbe destroyed by ultrasound the rhabdoid structure with coefficient of sedimentation 22s is allocated, edges has protective properties (223 antigen). This antigen is probably localized in membranes. The new class of a bacterial antigen — lipoteykhoyevy acid which can be isolated from streptococci, lactobacilli and nek-ry bacilli is described. Lipoteykhoyevy to - that is localized on a surface of a cytoplasmic membrane and is group-specific antigen. Lipoteykhoyevy to - that is constructed of 25 — 30 glycerophosphatic remains and a lipidic component (glycolipid). Part of the glycerophosphatic remains is replaced with glucose and D-alanine. Membrane antigens of the majority of pathogenic bacteriums are studied a little.

The cytoplasmatic fraction of bacteria differs in a certain originality: at it along with components of cytoplasm (ribosomes, granules, fragments of an endoplasmic reticulum, cellular juice) there are components of a kernel (DNA and, perhaps, nuclear proteins).

Therefore, subjecting cytoplasmatic fraction immunol, to the analysis, sometimes it is hard to say at the expense of what antigens activity is revealed.

The so-called total fraction of cytoplasm of enterobakteriya, a pertussoid microbe, cocci and other bacteria has weak antigenic activity. In cytoplasm of a number of bacteria the general antigens are found: between strains of the sort Nocardia and Streptomyces, Nocardia and Mycobacterum. Identical cytoplasma antigens are revealed at mycobacteria, actinomycetes and korinebakteriya. However in cytoplasm of a plague microbe specific antigens are found: fraction I, the «mouse» toxin, VW antigen and an antigenic complex taken by trichloroacetic processing. The listed antigens can be important in a pathogeny of an infection. On model of a plague microbe it is shown that the antigenic complexes received by method phenol — water, and the antigenic complex taken trichloroacetic to - that, are different antigens and, perhaps, are localized in different structures. From an ultrasonic lysate of shigellas Zeltman (G. Seltman, 1975) isolated the antigen moving to the anode (ATA) which was the general for many enterobakteriya. This antigen of the proteinaceous nature is probably located in a cell.

Antigens in ribosomes are revealed: during 1960 — 1963 it was established that in ribosomes of bacteria three types of antigens, the general for many bacteria (apparently, RNA), the general for limited number of types (squirrels) and specific to each look are localized. In 1967 — 1975 it is shown that the ribosomalny fractions received from enterobakteriya, listeriya, mycobacteria, pertussoid microbes, cholera vibrioes, stafilokokk have protective properties in experiences on laboratory animals. At the same time it is proved that protective activity of ribosomes is not connected with impurity of antigens of a cell wall. From ribosomalny fraction of a cholera vibrio the method of ion-exchange chromatography isolated protein, to-ry had specific protective properties, and the cleared ribosomes did not cause protection in animals. However one researchers assume that protective activity of ribosomes is connected with RNA, others — with protein, and the third consider that some carbohydrate «is attached» to the isolated ribosomes, perhaps, a cell wall which has specific properties of antigen. The mechanism of protective action of «ribosomalny» vaccines is not found out.

Researches of Ribi (E. Ribi) with sotr. existence in cytoplasm of enterobakteriya of low-molecular polysaccharide was shown, to-ry on antigenic properties and chemical structure it is close to O-antigen of a cell wall. This polysaccharide is described as plasmatic. Its antigenic activity is shown only when it is connected to O-antigen. However such complex does not cause antibody formation in rabbits. Plasmatic polysaccharide was designated as the native hapten constructed of «linear molecules» (particles), a pier. weight to-rykh is equal 163 000, to dia. — 1,6 nanometers, length — 130 nanometers. Molecules of native hapten, unlike O-antigen, do not form micelle structures. It is suggested that native hapten is a predecessor of O-antigen of a cell wall.

By many researchers it is established that bacterial DNA has antigenic properties. Drugs of bacterial DNA react as antigens with homologous and heterological serums. Reactivity between DNA of bacteria and DNA of cells of a macroorganism is shown cross serol.

Nek-ry researchers consider that DNA and nucleoproteids of bacteria stimulate autoimmune process.

Thus, bacteria have a difficult mosaic of antigens, to-rye are distributed almost in all structures and organellas ah. One of these antigens are more active, others — less. The question of identification and release of protective antigens in the cleared view with the purpose of production of effective vaccines and diagnostic drugs is most important from the practical point of view.

See also Antigens .



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Genetics B. — Brown V. Genetics of bacteria, the lane with English, M., 1968, bibliogr.; Jacob F.ivolman E. A floor and genetics of bacteria, the lane with English, M., 1962; Zakharov I. A. and K. V. Genetik's Receipt of microorganisms, JI., 1967; The Collection of techniques on genetics of microorganisms, under the editorship of R. Claus and U. Heys, lane with English, M., 1970, bibliogr.; With to and-vronskayaa.g. Mutations at bacteria, M., 1967, bibliogr.; T and at 1 about And. Z. and. T of 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 12-th international congress of genetics, v. 3, Tokyo, 1968; Sanderson Κ. E. Genetics of the Enterobacteriaceae, Advanc. Genet., v. 16, p. 35, 1971, bibliogr.

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B. S. Levashev; A. G. Skavronskaya (the gen. with the tab.); D. M. Goldfarb (bakt. tab.). E. S. Stanislavsky.

Яндекс.Метрика