Classification of microorganisms according to their main forms. How are bacteria classified?
2.2. Classification and morphology of bacteria
Classification of bacteria. The decision of the International Code for Bacteria recommends the following taxonomic categories: class, department, order, family, genus, species. The species name corresponds to the binary nomenclature, i.e. it consists of two words. For example, the causative agent of syphilis is written as Treponema pallidum. First word - na-
genus name and is written with capital letter, the second word denotes the species and is written with a lowercase letter. When a species is mentioned again, the generic name is abbreviated to the initial letter, for example: T.pallidum.
Bacteria are prokaryotes, i.e. pre-nuclear organisms, since they have a primitive nucleus without a shell, nucleolus, histones. and in the cytoplasm there are no highly organized organelles (mitochondria, Golgi apparatus, lysosomes, etc.)
In the old Burgey's Manual of Systematic Bacteriology, bacteria were divided into 4 sections according to the features of the bacterial cell wall: Gracilicutes - eubacteria with a thin cell wall, gram-negative; Firmicutes - thick-walled eubacteria, Gram-positive; Tenericutes - eubacteria without a cell wall; Mendosicutes - archaebacteria with a defective cell wall.
Each section was divided into sections, or groups, according to Gram stain, cell shape, oxygen demand, mobility, metabolic and nutritional characteristics.
According to the 2nd Edition (2001) of the ManualBergey, bacteria are divided into 2 domains:"Bacteria" and "Archaea" (Table 2.1).
Table. Domain characteristicsbacteriaandArchaea
|
Domain"Bacteria"(eubacteria) |
Domain"Archaea" (archaebacteria) |
|
In the "Bacteria" domain, one can distinguish the following bacteria: 1) bacteria with a thin cell wall, gram-negative*; 2) bacteria with a thick cell wall, gram-positive**; 3) bacteria beta cell wall (class Mollicutes - mycoplasmas) |
Archsbacteria do not contain peptidoglycan in the cell wall. They have special ribosomes and ribosomal RNA (rRNA). The term "archaebacteria" appeared in 1977. This is one of the ancient forms of life, as indicated by the prefix "arche". Among them there are no infectious agents |
*Among thin-walled Gram-negative eubacteria distinguish:
spherical forms, or cocci (gonococci, meningococci, veillonella);
convoluted forms - spirochetes and spirilla;
rod-shaped forms, including rickettsiae.
** To thick-walled gram-positive eubacteria include:
spherical shapes, or cocci (staphylococci, streptococci, pneumococci);
rod-shaped forms, as well as actinomycetes (branching, filamentous bacteria), corynebacteria (club-shaped bacteria), mycobacteria and bifidobacteria (Fig. 2.1).
Most Gram-negative bacteria are grouped under the Proteobacteria phylum. based on the similarity in ribosomal RNA "Proteobacteria" - named after the Greek god Proteus. taking on various forms). They appeared from the general photosynthesis tic ancestor.
Gram-positive bacteria, according to the studied ribosomal RNA sequences, are a separate phylogenetic group with two large subdivisions - with a high and low ratio G+ C (genetic similarity). Like proteobacteria, this group is metabolically diverse.
To the domain "bacteria» includes 22 types, from whichThe following are of medical importance:
Type ofProteobacteria
Class Alphaproteobacteria. childbirth: Rickettsia, Orientia, Ehrlichia, Bartonella, Brucella
Class Betaproteobacteria. childbirth: Burkholderia, Alcaligenes, Bordetella, Neisseria, Kingella, Spirillum
Class Gammaproteobacteria. childbirth: Francisella, Legionella, Coxiella, Pseudomonas, Moraxella, Acinetobacter, Vibrio, Enterobacter, Callimatobacterium, Citrobacter, Edwardsiella, Erwinia, Escherichia, Hafnia, Klebsiella, Morganella, Proteus, Providencia, Salmonella, Serratia, Shigella, Yersinia, Pasteurella
Class Deltaproteobacteria. Genus: Bilophila
Class Epsilonproteobacteria. childbirth: Campylobacter, Helicobacter, Wolinella
Type ofFirmicutes (mainwaygrampolo resident)
Class Clostridia. childbirth: Clostridium, Sarcina, Peptostreptococcus, Eubacterium, Peptococcus, Veillonella (gram-negative)
Class Mollicutes. Genera: Mycoplasma, Ureaplasma
Class bacilli. childbirth: Bacillus, Sporosarcina, Listeria, Staphylococcus, Gemella, Lactobacillus, Pediococcus, Aerococcus, Leuconostoc, Streptococcus, Lactococcus
Type ofActinobacteria
Class Actinobacteria. childbirth: Actinomyces, Arcanodacterium, Mobiluncus, Micrococcus, Rothia, Stomatococcus, Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, Bifidobacterium, Gardnerella
Type ofClamydiae
Class Clamydiae. childbirth: Clamydia, Clamydophila
Type ofSpirochaetes
Class Spirochaetes. childbirth: Spirochaeta, Borrelia, Treponema, Leptospira
Phylum Bacteroidetes
Class Bacteroidetes. childbirth: Bacteroides, Porphyromonas, Prevotella
Class Flavobacteria. Childbirth: Flavobacterium
The subdivision of bacteria according to the structural features of the cell wall is associated with the possible variability of their coloration in one color or another according to the Gram method. According to this method, proposed in 1884 by the Danish scientist H. Gram, depending on the staining results, bacteria are divided into gram-positive, stained blue-violet, and gram-negative, stained red. However, it turned out that bacteria with the so-called gram-positive type of cell wall (thicker than those of gram-negative bacteria), for example, bacteria of the genus Mobiluncus and some spore-forming bacteria, instead of the usual gram-positive color, have a gram-negative color. Therefore, for the taxonomy of bacteria, the features of the structure and chemical composition of cell walls are of greater importance than the Gram stain.
2.2.1. Shapes of bacteria
There are several basic forms of bacteria (see Fig. 2.1) - coccoid, rod-shaped, convoluted and branching, filamentous forms of bacteria.
Spherical shapes, or cocci,- spherical bacteria with a size of 0.5-1.0 microns *, which are divided by mutual arrangement into micrococci, diplococci, streptococci, tetracocci, sarcins and staphylococci.
micrococci(from Greek. micros - small) - separately located cells.
diplococci(from Greek. diploos - double), or paired cocci, arranged in pairs (pneumococcus, gonococcus, meningococcus), since the cells do not diverge after division. Pneumococcus (the causative agent of pneumonia) has a lanceolate shape on opposite sides, and gonococcus(the causative agent of gonorrhea) and meningococcus (the causative agent of epidemic meningitis) are shaped like coffee beans facing each other with a concave surface.
streptococci(from Greek. streptos - chain) - cells of a rounded or elongated shape that make up a chain due to cell division in the same plane and maintaining the connection between them at the place of division.
Sarcins(from lat. Sarcina - bundle, bale) are arranged in the form of packages of 8 or more cocci, as they are formed during cell division in three mutually perpendicular planes.
Staphylococci(from Greek. staphyle - bunch of grapes) - cocci, arranged in the form of a bunch of grapes as a result of division in different planes.
rod-shaped bacteria differ in size, shape of the ends of the cell and the relative position of the cells. Cell length varies from 1.0 to 10 µm, thickness - from 0.5 to 2.0 µm. Sticks can be correct (E. coli, etc.) and incorrect (Corynebacterium and etc.) forms, including branching, for example, in actinomycetes. Rickettsiae are among the smallest rod-shaped bacteria.
The ends of the sticks can be, as it were, cut off (anthrax bacillus), rounded (E. coli), pointed (fusobacteria) or in the form of a thickening. In the latter case, the stick looks like a mace (Corynebacterium diphtheria).
The slightly curved rods are called vibrios (Vibrio cholerae). Most rod-shaped bacteria are arranged randomly, because after division, the cells diverge. If cells remain connected after division,
mi common fragments of the cell wall and do not diverge, they are located at an angle to each other (corynebacterium diphtheria) or form a chain (anthrax bacillus).
Convoluted forms- spiral-shaped bacteria, for example spirilla, having the appearance of corkscrew-shaped convoluted cells. Pathogenic spirilla is the causative agent of sodoku (rat bite disease). The tortuous also include campylobacter and helicobacteria, which have curves like the wing of a flying gull; close to them are bacteria such as spirochetes. Spirochetes- thin, long, twisted
spiral-shaped) bacteria that differ from spirilla in mobility due to flexion changes in cells. Spirochetes are made up of an outer membrane
cell wall) surrounding the protoplasmic cylinder with a cytoplasmic membrane and an axial filament (axystyle). The axial filament is located under the outer membrane of the cell wall (in the periplasm) and, as it were, twists around the protoplasmic cylinder of the spirochete, giving it a helical shape (primary whorls of spirochetes). The axial filament consists of periplasmic fibrils, analogues of bacterial flagella, and is a contractile protein, flagellin. Fibrils are attached to the ends of the cell (Fig. 2.2) and directed towards each other. The other end of the fibrils is free. The number and location of fibrils vary in different types. Fibrils are involved in the movement of spirochetes, giving the cells rotational, flexion and translational motion. In this case, spirochetes form loops, curls, bends, which are called secondary curls. Spirochetes
dyes are poorly perceived. Usually they are stained according to Romanovsky-Giemsa or silvered. Live spirochetes are examined using phase-contrast or dark-field microscopy.
Spirochetes are represented by 3 genera pathogenic for humans: Treponema, Borrelia, Leptospira.
Treponema(genus Treponema) have the appearance of thin corkscrew-twisted threads with 8-12 uniform small curls. There are 3-4 fibrils (flagella) around the treponema protoplast. The cytoplasm contains cytoplasmic filaments. Pathogenic representatives are T.pallidum - causative agent of syphilis T.pertenue - the causative agent of a tropical disease - fram besia. There are also saprophytes - inhabitants of the human oral cavity, silt of reservoirs.
Borrelia(genus Borrelia), unlike treponemas, they are longer, have 3-8 large curls and 7-20 fibrils. These include the causative agent of relapsing fever (AT.recurrentis) and causative agents of Lyme disease (AT.burgdorferi and etc.).
Leptospira(genus Leptospira) have curls shallow and frequent - in the form of a twisted rope. The ends of these spirochetes are curved like hooks with thickenings at the ends. Forming secondary curls, they take the form of letters S or with; have 2 axial threads (flagella). Pathogenic representative L. in terrogans causes leptospirosis when ingested with water or food, leading to the development of hemorrhages and jaundice.
in the cytoplasm, and some in the nucleus of infected cells. They live in arthropods (lice, fleas, ticks) that are their hosts or carriers. Rickettsia got its name from X. T. Ricketts, an American scientist who first described one of the pathogens (Rocky Mountain spotted fever). The shape and size of the rickettsia may vary (irregularly shaped cells, filamentous) depending on the growth conditions. The structure of rickettsia does not differ from that of gram-negative bacteria.
Rickettsia have a metabolism independent of the host cell, however, it is possible that they receive macroergic compounds from the host cell for their reproduction. In smears and tissues, they are stained according to Romanovsky-Giemsa, according to Machiavello-Zdrodovsky (rickettsia are red, and infected cells are blue).
Rickettsia causes epidemic typhus in humans. (Rickettsia prowazekii), tick-borne rickettsiosis (R. sibirica), Rocky Mountain spotted fever (R. rickettsii) and other rickettsiosis.
Elementary bodies enter the epithelial cell by endocytosis with the formation of an intracellular vacuole. Inside the cells, they increase and turn into dividing reticular bodies, forming clusters in vacuoles (inclusions). From the reticular bodies, elementary bodies are formed, which exit the cells by exocytosis or cell lysis. Departed from
elementary body cells enter a new cycle, infecting other cells (Fig. 16.11.1). In humans, chlamydia causes damage to the eyes (trachoma, conjunctivitis), urogenital tract, lungs, etc.
actinomycetes- branching, filamentous or rod-shaped gram-positive bacteria. Its name (from the Greek. actis - Ray, mykes - mushroom) they received in connection with the formation of drusen in the affected tissues - granules of tightly interwoven threads in the form of rays extending from the center and ending in bulb-shaped thickenings. Actinomycetes, like fungi, form mycelium - filamentous intertwining cells (hyphae). They form substrate mycelium, which is formed as a result of cells growing into the nutrient medium, and air, growing on the surface of the medium. Actinomycetes can divide by fragmenting the mycelium into cells similar to rod-shaped and cocci-shaped bacteria. On aerial hyphae of actinomycetes, spores are formed that serve for reproduction. Actinomycete spores are usually not heat resistant.
A common phylogenetic branch with actinomycetes is formed by the so-called nocardi-like (nocardioform) actinomycetes, a collective group of rod-shaped, irregularly shaped bacteria. Their individual representatives form branching forms. These include bacteria of the genera Corynebacterium, Mycobacterium, Nocardianjxp. Nocardio-like actinomycetes are distinguished by the presence in the cell wall of sugars of arabinose, galactose, as well as mycolic acids and large amounts of fatty acids. Mycolic acids and cell wall lipids determine the acid resistance of bacteria, in particular Mycobacterium tuberculosis and leprosy (when stained according to Ziehl-Nelsen, they are red, and non-acid-resistant bacteria and tissue elements, sputum are blue).
Pathogenic actinomycetes cause actinomycosis, nocardia - nocardiosis, mycobacteria - tuberculosis and leprosy, corynebacteria - diphtheria. Saprophytic forms of actinomycetes and nocardia-like actinomycetes are widespread in the soil, many of them are producers of antibiotics.
cell wall- a strong, elastic structure that gives the bacteria a certain shape and, together with the underlying cytoplasmic membrane, "restrains" the high osmotic pressure in the bacterial cell. It is involved in the process of cell division and transport of metabolites, has receptors for bacteriophages, bacteriocins and various substances. The thickest cell wall in gram-positive bacteria (Fig. 2.4 and 2.5). So, if the thickness of the cell wall of gram-negative bacteria is about 15-20 nm, then in gram-positive bacteria it can reach 50 nm or more.
Mycoplasmas- small bacteria (0.15-1.0 microns), surrounded only by the cytoplasmic membrane. They belong to the class Mollicutes, contain sterols. Due to the lack of a cell wall, mycoplasmas are osmotically sensitive. They have a variety of shapes: coccoid, filiform, flask-shaped. These forms are visible on phase-contrast microscopy of pure cultures of mycoplasmas. On a dense nutrient medium, mycoplasmas form colonies resembling fried eggs: a central opaque part immersed in the medium and a translucent periphery in the form of a circle.
Mycoplasmas cause SARS in humans (Mycoplasma pneumoniae) and lesions of the urinary tract (M.homi- nis and etc.). Mycoplasmas cause diseases not only in animals but also in plants. Non-pathogenic representatives are quite widespread.
2.2.2. Structure of a bacterial cell
The structure of bacteria has been well studied using electron microscopy of whole cells and their ultrathin sections, as well as other methods. A bacterial cell is surrounded by a membrane consisting of a cell wall and a cytoplasmic membrane. Under the shell is protoplasm, consisting of cytoplasm with inclusions and a nucleus called the nucleoid. There are additional structures: capsule, microcapsule, mucus, flagella, pili (Fig. 2.3). Some bacteria under adverse conditions are able to form spores.
In the cell wall of Gram-positive bacteria contains a small amount of polysaccharides, lipids, proteins. The main component of the cell wall of these bacteria is a multilayer peptidoglycan (mu-rein, mucopeptide), which makes up 40-90% of the mass of the cell wall. Teichoic acids (from the Greek. teichos - wall), the molecules of which are chains of 8-50 residues of glycerol and ribitol connected by phosphate bridges. The shape and strength of the bacteria is given by the rigid fibrous structure of the multilayer, cross-linked peptide peptidoglycan.
Peptidoglycan is represented by parallel molecules glycana. consisting of repeating residues of N-acetylglucosamine and N-acetylmuramic acid connected by a glycosidic bond. These bonds are broken by lysozyme, which is an acetylmuramidase. Glycan molecules are connected via N-acetylmuramic acid by a four amino acid cross-peptide bond ( tetrapeptide). Hence the name of this polymer - peptidoglycan.
The basis of the peptide bond of the peptidoglycan of gram-negative bacteria is tetrapeptides, consisting of alternating L- and D-amino acids, for example: L-alanine - D-glutamic acid - meso-diaminopimelic acid - D-alanine. At E.coli (gram-negative bacterium) peptide chains are connected to each other through D-alanine of one chain and meso-diaminopimel-
new acid - another. The composition and structure of the peptide part of the peptidoglycan of gram-negative bacteria are stable, in contrast to the peptidoglycan of gram-positive bacteria, the amino acids of which may differ in composition and sequence. Peptidoglycan tetrapeptides in Gram-positive bacteria are connected to each other by polypeptide chains of 5 residues.
glycine (pentaglycine). Instead of meso-diamino-pimelic acid, they often contain lysine. Glycan elements (acetylglucosamine and acetylmuramic acid) and tetra-peptide amino acids (meso-diaminopimelic and D-glutamic acids, D-alanine) are a distinctive feature of bacteria, since they are absent in animals and humans.
The ability of gram-positive bacteria to retain gentian violet in combination with iodine (blue-violet color of bacteria) during Gram staining is associated with the property of multilayer peptidoglycan to interact with the dye. In addition, the subsequent treatment of a smear of bacteria with alcohol causes narrowing of the pores in 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, become red.
AT composition of the cell wall of gram-negative bacteria the outer membrane enters, connected by means of a lipoprotein to the underlying layer of peptidoglycan (Fig. 2.4 and 2.6). The outer membrane on electron microscopy of ultrathin sections of bacteria has the form of a wavy three-layer structure similar to the inner membrane, which is called cytoplasmic. The main component of these membranes is a bimolecular (double) layer of lipids.
The outer membrane is a mosaic structure represented by lipopolysaccharides, phospholipids and proteins. Its inner layer is represented by phospholipids, and in the outer layer is located lipopolysaccharide(LPS). Thus, the outer membrane is asymmetric. The LPS of the outer membrane consists of three fragments:
lipid A - a conservative structure, almost the same in gram-negative bacteria;
core, or rod, bark part (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 determines the toxicity of LPS and is therefore identified with endotoxin. The destruction of bacteria by antibiotics leads to the release of large amounts of endotoxin, which can cause endotoxic shock in the patient. From lipid A, the core, or the core part of the LPS, departs. The most constant part of the LPS core is keto-deoxyoctonic acid (3-deoxy-O-man-no-2-octulosonic acid). The O-specific chain extending from the core part of the LPS molecule determines the serogroup, serovar (a type of bacteria detected using immune serum) of a certain bacterial strain. Thus, the concept of LPS is associated with ideas about the O-antigen, according to which bacteria can be differentiated. Genetic changes can lead to defects, "shortening" of the LPS of bacteria and the appearance of "rough" colonies of R-forms as a result.
Proteins of the matrix of the outer membrane penetrate it in such a way that protein molecules called porins border hydrophilic pores through which water and small hydrophilic molecules with a relative mass of up to 700 Da pass.
Between the outer and cytoplasmic membranes is the periplasmic space, or periplasm, containing enzymes (proteases, lipases, phosphatases,
nucleases, beta-lactamases), as well as components of transport systems.
In case of violation of the synthesis of the bacterial cell wall 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 devoid of a cell wall; spheroplasts are bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, i.e. acquire a full-fledged cell wall and restore their original shape.
Sphero- or protoplast-type bacteria that have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to multiply are called L-forms (from the name of the D. Lister Institute, where they were first studied). L-forms can also arise as a result of mutations. They are osmotically sensitive, spherical, flask-shaped cells of various sizes, including those passing through bacterial filters. Some L-forms (unstable) when the factor that led to changes in the bacteria is removed, can reverse, "returning" to the original bacterial cell. L-forms can form many pathogens of infectious diseases.
cytoplasmic membrane ana under electron microscopy of ultrathin sections, it is a three-layer membrane (2 dark layers 2.5 nm thick each are separated by a light one - intermediate). In structure (see Fig. 2.5 and 2.6), it is similar to the plasmalemma of animal cells and consists of a double layer of lipids, mainly phospholipids, with embedded surface and integral proteins, as if penetrating through the membrane structure. Some of them are permeases involved in the transport of substances.
The cytoplasmic membrane is a dynamic structure with mobile components, therefore it is presented as a mobile fluid structure. It surrounds the outer part of the bacterial cytoplasm and is involved in the regulation of osmotic pressure.
ion, transport of substances and energy metabolism of the cell (due to the enzymes of the electron transport chain, adenosine triphosphatase, etc.).
With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complexly twisted membrane structures, called mesosomes. Less complex twisted structures are called intracytoplasmic membranes. The role of mesosomes and intracytoplasmic membranes has not been fully elucidated. It is even suggested that they are an artifact that occurs after the preparation (fixation) of the preparation 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, take part in the secretion of substances, sporulation, i.e., in processes with a high energy consumption.
The cytoplasm occupies the main volume of the bacterial cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes responsible for the synthesis (translation) of proteins.
Bacterial ribosomes are about 20 nm in size and have a sedimentation coefficient of 70S, in contrast to the SOS ribosomes characteristic of eukaryotic cells. Therefore, some antibiotics bind to bacterial ribosomes and inhibit bacterial protein synthesis without affecting protein synthesis in eukaryotic cells. Bacterial ribosomes can dissociate into two subunits, 50S and 30S. Ribosomal RNA (rRNA) are conservative elements of bacteria ("molecular clock" of evolution). 16S rRNA is part of the small subunit of ribosomes, and 23S rRNA is part of the large subunit of ribosomes. The study of 16S rRNA is the basis of gene systematics, making it possible to assess the degree of relatedness of organisms.
In the cytoplasm there are various inclusions in the form of glycogen granules, polysaccharides, beta-hydroxybutyric acid and polyphosphates (volutin). They accumulate when there is an excess of nutrients in the environment and
play the role of 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. Toluidine blue or methylene blue stains volutin red-violet, and the bacterial cytoplasm blue. The characteristic arrangement of volutin granules is revealed in diphtheria bacillus in the form of intensely stained poles of the cell. Metachromatic staining of volutin is associated with a high content of polymerized inorganic polyphosphate. Under electron microscopy, they look like electron-dense granules 0.1-1.0 µm in size.
Nucleoid is the equivalent of the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, closed in a ring and tightly packed like a ball. The nucleus of bacteria, unlike eukaryotes, does not have a nuclear membrane, nucleolus and basic proteins (histones). Usually, a bacterial cell contains one chromosome, represented by a DNA molecule closed in a ring. If division is disturbed, 4 or more chromosomes can converge in it. The nucleoid is detected in a light microscope after staining with DNA-specific methods: according to Feulgen or Romanovsky-Giemsa. On the electron diffraction patterns of ultrathin sections of bacteria, the nucleoid has the form of light zones with fibrillar, filamentous DNA structures associated with certain areas with
cytoplasmic membrane or mesoso-
mine involved in chromosome replication (see Figures 2.5 and 2.6).
In addition to the nucleoid represented by one
chromosome, in a bacterial cell there are
extrachromosomal factors of heredity -
plasmids (see section 5.1.2.), representing
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 outer boundaries. The capsule is distinguishable in smears-imprints from pathological material. In pure cultures of bacteria, the capsule is formed
less often. It is detected with special Burri-Gins smear staining methods that create a negative contrast of the capsule substances: the ink creates a dark background around the capsule.
The capsule consists of polysaccharides (exopolysaccharides), sometimes polypeptides; for example, in the anthrax bacillus, it consists of polymers of D-glutamic acid. The capsule is hydrophilic, contains a large amount of water. It prevents phagocytosis of bacteria. Capsule antigen-on: antibodies against the capsule cause it increase (response to swell and I capsule ly).
Many bacteria form a microcapsule - a slimy formation less than 0.2 microns thick, detected only with electron microscopy. Mucus should be distinguished from the capsule - mucoid exopolysaccharides that do not have clear external boundaries. Slime 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); also called glyco-
calix. In addition to the synthesis of exopolysaccharides by bacteria, there is another mechanism for their formation: through the action of extracellular bacterial enzymes on disaccharides. As a result, dextrans and levans are formed.
The capsule and mucus protect bacteria from damage and drying out, since, being hydrophilic, they bind water well and prevent the action of protective factors of the macroorganism and bacteriophages.
Flagella bacteria determine the mobility of the bacterial cell. Flagella are thin filaments originating from the cytoplasmic membrane and are longer than the cell itself (Fig. 2.7). The flagella are 12–20 nm thick and 3–15 µm long. They consist of 3 parts: a spiral thread, a hook and a basal body containing a rod with special discs (1 pair of discs in gram-positive and 2 pairs in gram-negative bacteria). The discs of the flagella are attached to the cytoplasmic membrane and cell wall. This creates the effect of an electric motor with a rod - a rotor that rotates the flagellum. The difference of proton potentials on the cytoplasmic membrane is used as an energy source. The rotation mechanism is provided by proton ATP synthetase. The speed of rotation of the flagellum can reach 100 rpm. If a bacterium has several flagella, they begin to rotate synchronously, intertwining into a single bundle, forming a kind of propeller.
Flagella are made up of a protein called flagellin. flagellum - flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are coiled.
The number of flagella in bacteria of various species varies from one (monotrich) in Vibrio cholerae to ten or hundreds of flagella extending along the perimeter of the bacterium (peritrich), in Escherichia coli, Proteus, etc. Lophotrichous have a bundle of flagella at one end of the cell. Amphitrichous have 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 processing by 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 drank(fimbria) - filamentous formations (Fig. 2.7), thinner and shorter (3 + 10 nm x 0.3 + 10 microns) than flagella. Pili extend from the cell surface and are composed of the pilin protein. They have antigenic activity. There are pili responsible for adhesion, i.e., for attaching bacteria to the affected cell, as well as pili responsible for nutrition, water-salt metabolism, and sexual (F-pili), or conjugation, drank.
Usually drank are numerous - several hundred per cage. However, she usually has 1-3 sex saws per cell: they are formed by the so-called "male" donor cells containing transmissible plasmids (F-, R-, Sol-plasmids). A distinctive feature of sex pili is their interaction with special "male" spherical bacteriophages, which are intensively adsorbed on sex pili (Fig. 2.7).
controversy- a peculiar form of resting bacteria with a gram-positive type of cell wall structure (Fig. 2.8).
Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.). Inside the bacterial cell, one spore (endospore) is formed. The formation of spores contributes to the preservation of the species and is not a method of reproduction, as in fungi.
spore-forming bacteria of the genus bacillus, y whose spore size does not exceed the diameter of the cell are called bacilli. Spore-forming bacteria, in which the spore size exceeds the cell diameter, which is why they take the form of a spindle, are called clostridia, for example, bacteria of the genus Clostridium (lat. Clostridium - spindle). The spores are acid-resistant, therefore they are stained red according to the Aujeszky method or according to the Ziehl-Nelsen method, and the vegetative cell is blue.
Sporulation, the shape and location of spores in a cell (vegetative) are a species property of bacteria, which makes it possible to distinguish them from each other. The shape of the dispute can be oval, spherical; the location in the cell is terminal, that is, at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in causative agents of botulism, gas gangrene) and central in the anthrax bacillus).
Process spore formation(sporulation) goes through a series of stages, during which a part of the cytoplasm and the chromosome of a bacterial vegetative cell are separated, surrounded by a growing cytoplasmic membrane, and a prospore is formed. The prospore is surrounded by two cytoplasmic membranes, between which a thick altered peptidoglycan layer of the cortex (bark) is formed. From the inside, it comes into contact with the cell wall of the spore, and from the outside - with the inner shell of the spore. The outer shell of the spore is formed by a vegetative cell. Spores of some bacteria have an additional cover - exosporium. Thus, a multilayer poorly permeable shell is formed. Sporulation is accompanied by intensive consumption of dipicolinic acid and calcium ions by the prospore, and then by the emerging spore shell. 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 multi-layered shell, calcium dipicolinate, low water content and sluggish metabolic processes. In the soil, for example, anthrax and tetanus pathogens can persist for decades.
Under favorable conditions, spores germinate, passing through three successive stages:
initiation, initiation, growth. In this case, one bacterium is formed from one spore. Activation is the readiness for germination. At a temperature of 60-80 °C, the spore is activated for germination. Germination initiation takes several minutes. The growth stage is characterized by rapid growth, accompanied by the destruction of the shell and the release of the seedling.
Bacteria are prokaryotic microorganisms of the cellular structure. Their sizes are from 0.1 to 30 microns. Microbes are extremely common. They live in soil, air, water, snow and even hot springs, on the body of animals, as well as inside living organisms, including the human body.
The distribution of bacteria into species is based on several criteria, among which the shape of microorganisms and their spatial distribution are most often taken into account. So, according to the shape of the cells, bacteria are divided into:
Coci - micro-, diplo-, strepto-, staphylococci, as well as sarcins;
Rod-shaped - monobacteria, diplobacteria and streptobacteria;
Convoluted species - vibrios and spirochetes.
Burgey's determinant systematizes all known bacteria according to the principles of bacterial identification that have found the widest distribution in practical bacteriology, based on differences in the structure of the cell wall and in relation to Gram stain. The description of bacteria is given by groups (sections), which include families, genera and species; in some cases, groups include classes and orders. Bacteria pathogenic to humans are included in a small number of groups.
The key distinguishes four main categories of bacteria -
Gracillicutes [from lat. gracilis, graceful, thin, + cutis, skin] - species with a thin cell wall, stained gram negative;
firmicutes [from lat. flrmus, strong, + cutis, skin] - bacteria with a thick cell wall, staining gram positive;
Tenericutes [from lat. tener, gentle, + cutis, skin] - bacteria lacking a cell wall(mycoplasmas and other members of the class Mollicutes)
Mendosicutes [from lat. mendosus, irregular, + cutis, skin] - archaebacteria (methane- and sulfate-reducing, halophilic, thermophilic and archaebacteria, devoid of a cell wall).
Group 2 Burgey's determinant. Aerobic and microaerophilic motile convoluted and curved Gram-negative bacteria. Species pathogenic for humans are included in the genera Campylobacter, Helicobacters Spirillum.
Group 3 of Bergey's determinant. Non-motile (rarely motile) Gram-negative bacteria. Does not contain pathogenic species.
Group 4 of Burgey's determinant. Gram-negative aerobic and microaerophilic rods and cocci. Species pathogenic for humans are included in the Legionellaceae, Neisseriaceae and Pseudomonada-ceae families, the group also includes pathogenic and opportunistic bacteria of the genera Acinetobacter, Afipia, Alcaligenes, Bordetella, Brucella, Flavobacterium, Francisella, Kingella and Moraxella.
Group 5 of Bergey's determinant. Facultative anaerobic Gram-negative rods. The group is formed by three families - Enterobacteriaceae, Vibrionaceae and Pasteurellaceae, each of which includes pathogenic species, as well as pathogenic and opportunistic bacteria of the genera Calymmobaterium, Cardiobacterium, Eikenetta, Gardnerella and Streptobacillus.
Group 6 of Bergey's determinant. Gram-negative anaerobic straight, curved and spiral bacteria. Pathogenic and opportunistic species are included in the genera Bacteroides, Fusobacterium, Porphoromonas and Prevotelta.
Group 7 of Bergey's determinant. Bacteria that perform dissimilation reduction of sulfate or sulfur Does not include pathogenic species.
Group 8 of Bergey's determinant. Anaerobic Gram-negative cocci. Includes opportunistic bacteria of the genus Veillonella.
Group 9 of Bergey's determinant. Rickettsia and chlamydia. Three families - Rickettsiaceae, Bartonellaceae and Chlamydiaceae, each of which contains species pathogenic to humans.
Groups 10 and 11 of the Burgey's guide include anoxy- and oxygenic phototrophic bacteria that are not pathogenic to humans.
Group 12 of Burgey's determinant. Aerobic chemolithotrophic bacteria and related organisms. It combines sulfur-iron- and manganese-oxidizing and nitrifying bacteria that do not cause damage to humans.
Groups 13 and 14 of Burgey's guide include budding and/or outgrowth bacteria and sheath-forming bacteria. Represented by free-living species, not pathogenic for humans;
Groups 15 and 16 of the Burgey's guide unite gliding bacteria that do not form fruiting bodies and form them. The groups do not include species pathogenic to humans.
Group 17 of Burgey's determinant. Gram-positive cocci. Includes opportunistic species of the genera Enterococcus Leuconostoc, Peptococcus, Peptostreptococcus, Sarcina, Staphylococcus, Stomatococcus, Streptococcus.
Group 18 of Burgey's determinant. Spore-forming Gram-positive rods and cocci. Includes pathogenic, conditionally pathogenic rods of the genera Clostridium and Bacillus.
Group 19 of Burgey's determinant. Spore-forming Gram-positive rods of regular shape. Including opportunistic species of the genera Erysipelothrix and Listeria.
Group 20 of Burgey's determinant. Irregularly shaped spore-forming Gram-positive rods. The group includes pathogenic and opportunistic species of the genera Actinomyces, Corynebacterium Gardnerella, Mobiluncus, etc.
Group 21 of Burgey's determinant. Mycobacteria. Includes the only genus Mycobacterium, which combines pathogenic and opportunistic species.
Groups 22-29. Actinomycetes. Among numerous species, only nocardioform actinomycetes (Group 22) of the genera Gordona, Nocardia, Rhodococcus, Tsukamurella, Jonesia, Oerskovi, and Terrabacter are capable of causing lesions in humans.
Group 30 of Burgey's determinant. Mycoplasmas. Species included in the genus Acholeplasma, Mycoplasma and Ureaplasma are pathogenic for humans.
The remaining groups of Bergey's determinant - methanogenic bacteria (31), sulfate-reducing bacteria (32 extremely halophilic aerobic archaebacteria (33), archaebacteria devoid of a cell wall (34), extreme thermophiles and hyperthermophiles, metabolizing sulfur (35) - do not contain species pathogenic to humans.
The modern classification (grouping) of microorganisms was proposed in 1980 by an American microbiologist bergy. According to this classification, the whole world of microbes is divided into three kingdoms: bacteria, fungi, viruses.
Who are they? To find out, I went to the school library, where our librarian helped me to work through the literature in search of an answer.
Name microorganisms comes from the Latin word micros - small. Therefore, microorganisms (microbes) are unicellular organisms less than 0.1 mm in size, which cannot be seen with the naked eye.
Appeared on Earth many billions of years before the appearance of man! They have a variety of shapes. Some are immobile, while others have cilia or flagella with which they move.
Most microbes breathe air aerobes.
For others, the air is harmful - it is anaerobes.
In the world classification, microbes are divided into pathogenic(pathogenic) and non-pathogenic microbes. These include bacteria, viruses, lower microscopic fungi (mucor, yeast) and algae, protozoa (
).
Attachment 1
Classification of microorganisms
From the lessons of the world around me, I learned that bacteria, previously considered microscopic plants, are now separated into an independent kingdom of Bacteria - one of four in the current classification system, along with plants, animals, fungi.
(other Greek - stick) - these are unicellular microorganisms, characterized by cellular similarities, having a variety of shapes: spherical - cocci, rod-shaped - bacilli, curved - vibrios, spiral - spirilla, in the form of a chain - streptococci, in the form of clusters - staphylococci (
).
Annex 2
Classification of bacteria by shape
| bacterium name | Bacteria shape | Bacteria image |
| cocci | spherical | |
| Bacillus | rod-shaped | |
| Vibrio | curved, comma |  |
| Spirillum | Spiral |  |
| streptococci | Chain |  |
| Staphylococci | bunches |  |
| diplococci | Two round bacteria in one capsule |
About ten thousand species of bacteria have been described so far. The branch of microbiology deals with the study of bacteria bacteriology.
(lat. virus poison) - the most primitive organisms on earth with a size of 20-300 nm. They reproduce only inside the living cells of the body. They do not have a cellular structure. In the free state, no metabolic processes occur in them.
(lower) are unicellular fungi. These mushrooms include the well-known white mold ( mukor mushroom). Such a fungus often develops on bread or vegetables and looks at first like cotton wool - a white fluffy substance that gradually turns black. Despite the fact that in everyday life mucor causes damage, in nature it plays a useful function, decomposing dead organisms.
A special niche in microbiological research is occupied by a group of unicellular fungi that live in a liquid medium, rich in organic matter used in fermentation processes.
(cyanobacteria) is a type of the oldest large bacteria capable of photosynthesis, accompanied by the release of oxygen.
- many different organisms, the body of which consists of a single cell ( infusoria, amoeba, green euglena...).
Thus, according to the classification I have considered, there is a huge number of microorganisms that exist and multiply in conditions that are comfortable for each species. Each type of microorganisms will depend on the habitat and perform certain functions.
Bacteria are single-celled organisms that lack chlorophyll.
bacteria are ubiquitous, inhabiting all habitats. The largest number of them is found in the soil at a depth of up to 3 km (up to 3 billion in one gram of soil). There are many of them in the air (at an altitude of up to 12 km), in the organisms of animals and plants (both living and dead), and the human body is no exception.
Among bacteria, there are fixed and mobile forms. Bacteria move with the help of one or more flagella, which are located on the entire surface of the body or in a specific area.
Bacterial cells are diverse in shape:
- spherical - cocci,
- rod-shaped - bacilli,
- in the form of a comma - vibrios,
- convoluted - spirilla.
cocci:
Monococci: they are separate cells.
Diplococci: these are paired cocci, after division they can form pairs.
Neisser's gonococcus: the causative agent of gonorrhea
Pneumococci: the causative agent of lobar pneumonia
Meningococci: the causative agent of meningitis (acute inflammation of the meninges)
Streptococci: These are cells of a rounded shape, which, after division, form chains.
α - viridescent streptococci
β - hemolytic streptococci, the causative agents of scarlet fever, tonsillitis, pharyngitis ...
γ - non-hemolytic streptococci
Staphylococci: this is a group of microorganisms that has not dispersed after division, forms huge random clusters.
Pathogen: pustular diseases, sepsis, boils, abscesses, phlegmon, mastitis, pyodermatitis and pneumonia in newborns.
Sarcins: this is the accumulation of cocci in groups in the form of bags of 8 or more cocci.
Rod-shaped:
These are bacteria of a cylindrical shape, similar to rods 1-5 × 0.5-1 μm in size, more often located singly .
Actually bacteria: These are rod-shaped bacteria that do not form spores.
Bacilli: These are rod-shaped bacteria that form spores.
(Koch's bacillus, Escherichia coli, anthrax, Pseudomonas aeruginosa, plague pathogen, whooping cough pathogen, chancre pathogen, tetanus pathogen, botulism pathogen, pathogen ...)
Vibrios:
These are slightly curved cells resembling commas 1-3 µm in size.
Vibrio cholerae: the causative agent of cholera. Lives in water through which infection occurs.
Spirilla:
These are convoluted microorganisms in the form of a spiral, with one, two or more spiral rings.
Harmless bacteria living in sewage and dammed reservoirs.
Spirochetes:
These are thin long ax-shaped bacteria, represented by three types: Treponema, Borrelia, Lertospira. Treponema pallidum is pathogenic for humans - the causative agent of syphilis is sexually transmitted.
The structure of a bacterial cell:
Structure of a bacterial cell well studied by electron microscopy. A bacterial cell consists of a shell, the outer layer of which is called the cell wall, and the inner one is the cytoplasmic membrane, as well as the cytoplasm with inclusions and nucleotides. There are additional structures: capsule, microcapsule, mucus, flagella, pili, plasmids;
cell wall - a strong, elastic structure that gives the bacteria a certain shape, and "restrains" the high osmotic pressure in the bacterial cell. It protects the cell from the action of harmful environmental factors.
outer membrane represented by lipopolysaccharides, phospholipids and proteins. On its outer side is a lipo-polysaccharide.
Between the cell wall and the cytoplasmic membranes is the periplasmic space, or periplasm, containing enzymes.
cytoplasmic membrane adjacent to the inner surface of the bacterial cell wall and surrounds the outer part of the bacterial cytoplasm. It consists of a double layer of lipids, as well as integral proteins penetrating through it.
Cytoplasm occupies the bulk of the bacterial cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosome, responsible for the synthesis of proteins. In the cytoplasm there are various inclusions in the form of glycogen granules, polysaccharides, fatty acids and polyphosphates.
Nucleotide - bacterial equivalent of the nucleus. It is located in the cytoplasm of bacteria in the form of two stranded DNA, closed in a ring and tightly packed like a ball. Usually, a bacterial cell contains one chromosome, represented by a DNA molecule closed in a ring.
In addition to the nucleotide in the bacterial cell, there may be extrachromosomal factors of heredity - plasmids, which are covalently closed DNA rings and capable of replication independently of the bacterial chromosome.
Capsule - a mucous structure that is firmly associated with the bacterial cell wall and has clearly defined outer boundaries. Usually the capsule consists of polysaccharides, sometimes poly-peptides,
Many bacteria contain microcapsule - mucous formation, detected only with electron microscopy.
Flagella bacteria determine cell motility. Flagella are thin filaments originating from the cytoplasmic membrane, they are attached to the cytoplasmic membrane and the cell wall by special disks, they are long, they consist of a protein - flagellin, twisted in a spiral. Flagella are detected using an electron microscope.
controversy - a peculiar form of dormant gram-positive bacteria formed in the external environment under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.).
L-shaped bacteria.
In many bacteria, with partial or complete destruction of cell walls, L-forms are formed. For some, they occur spontaneously. The formation of L-forms occurs under the action of penicillin, which disrupts the synthesis of cell wall mucopeptides. According to the morphology, the L-forms of different bacterial species are similar to each other. They are spherical, formations of various sizes: from 1-8 microns to 250 nm, they are capable, like viruses, of passing through the pores of porcelain filters. However, unlike L-form viruses, it can be grown on artificial nutrient media by adding penicillin, sugar, and horse serum to them. When penicillin is removed from the nutrient medium, the L-forms are again converted into the original forms of bacteria.
At present, L-forms of Proteus, Escherichia coli, Vibrio cholerae, Brucella, pathogens of gas gangrene and tetanus and other microorganisms have been obtained.
Gram-positive microorganisms (gr + m / o).
These include: aureus and epidermal staphylococcus aureus and streptococcus ...
Habitat: upper respiratory tract and skin.
Reservoir: skin, air, care items, furniture, bedding, clothes.
They do not die when dried.
Reproduction: they do not reproduce outside of a person, but are capable of reproduction in food products if stored improperly.
Gram-negative microorganisms (gr - m / o).
These include: E. coli, Klebsiella, citrobacter, Proteus, Pseudomonas aeruginosa ...
Habitat: intestines, mucosa of the urinary and respiratory tract ...
Reservoir : wet rags, dishwashing brushes, breathing equipment, wet surfaces, medicinal and mild disinfectants. solutions.
They die when dried.
Reproduction: accumulate in the external environment, in des. low concentration solutions.
Transmitted: airborne and contact-household way.
Bacteria are prokaryotes, single-celled organisms that do not have a nucleus. They are divided into two kingdoms: Bacteria and Archaebacteria. Among the latter there are no pathogens of infectious diseases. To date, the classification of bacteria is based on the principles of genetic communication.
The superkingdom of Bacteria is formed by the following organisms:
- thin-walled (gram-negative);
- thick-walled (gram-positive);
- without cell walls (mycoplasmas).
Within the superkingdom, microorganisms are classified into six taxonomic groups:
- Class.
- Order.
- Family.
The main group is the species. It is presented as a set of individuals with the same genesis and genotype, related by similar features and different from other species.
The name of the species is determined by binary nomenclature (that is, the name is formed from two words). The causative agent of syphilis, for example, is designated as Treponema pallidum. The first part of the name denotes the genus, it is indicated with a capital letter. The second indicates the species, it is written with a small letter. If the species is mentioned a second time, the genus name is indicated by the initial letter (T. padillum).
The most common is considered to be the phenotypic grouping included in the ninth edition of Burgey's Key. Its principles are based on the structure of the cell walls.
Burgey's determinant also classifies bacteria by Gram stain. The Gram technique is a research method in which staining allows differentiating organisms by the biochemical properties of their cell walls. The method was developed in 1884 by the Danish physician Gram.
The largest groups of bacteria in Burgey's classification are:
- Gram negative.
- Gram-positive.
- Mycoplasmas.
- Archaea.
Descriptions are presented in Burgey's guide by groups, including families, genera, and species. Sometimes classes and orders are included in the group. Burgey's key distinguishes 30 groups that include pathogenic organisms, the remaining 5 groups according to Burgey do not contain pathogenic species.
AT last years phylogenetic classification, which is based on the principles of molecular biology, is gaining popularity. In the 60s of the last century, one of the first ways to determine family ties by the similarity of the genome was discovered - a method for comparing the concentration of guanine (element nucleic acid) and cytosine (a constituent of DNA) in the DNA macromolecule. Identical indicators of their concentration do not indicate the evolutionary similarity of microorganisms, but a difference of 10% indicates that bacteria belong to different genera.
In the 1970s, another technique was developed that radically changed the theory of microbiology - the evaluation of the gene sequence in 16s rRNA. Using this method, it became possible to identify several phylogenetic groups of microorganisms and analyze their relationship.
Classification at the species level is carried out using the DNA-DNA hybridization technique. The study of thoroughly studied species shows that 70% of the degree of hybridization describe one species, from 10% to 60% - one genus, less than 10% - different genera.
The phylogenetic classification partially copies the phenotypic one. So, for example, gram-negatives are included in both. At the same time, the system of gram-negative organisms is almost completely modified. Archaebacteria are defined as an independent taxon of the highest level, some taxonomic groups are redistributed, microorganisms with different ecological purposes are assigned to one category.
Shapes of bacteria
Bacteria can be classified based on their morphology. One of the main morphological features is shape.
There are several varieties:
- Spherical (cocci, diplococci, sarcins, streptococci, staphylococci).
- Rod-shaped (bacilli, diplobacilli, streptobacilli, coccobacteria).
- Ornate (vibrio, spirilla).
- Spiral-shaped (spirochetes are thin, elongated, sinuous microorganisms with many curls).
- Filamentous.
The figure shows their forms:
- 1 - micrococci;
- 2 - streptococci;
- 3 - sarcins;
- 4 - non-spore sticks;
- 5 - spore rods (bacilli);
- 6 - vibrios;
- 7 - spirochetes;
- 8 - flagellated spirilla;
- 9 - staphylococci.
Spherical bacteria have a spherical shape, there are also oval and bean-shaped organisms.
Location of cocci:
- Separately - micrococci.
- Paired with diplococci.
- In chains - streptococci.
- In the shape of vine- staphylococci.
- In the "packages" - sarcins.
The most common are rod-shaped bacteria. The rods are collected singly, in pairs (diplobacteria) or in chains (streptobacteria). A number of rod-shaped organisms can form spores under severe conditions. Bacilli are spore rods. Spindle-shaped bacilli are called clostridia.
Ornate microorganisms have the form of a comma (vibrio), a thin sinuous rod (spirochete), and may also have several curls (spirilla).
Archaebacteria do not have peptidoglycan (a component that performs a mechanical function) in their cell walls. They have specific ribosomes and ribosomal RNA (ribonucleic acid).
Morphology of thin-walled Gram-negative organisms:
- Spherical shape (gonococcus, meningococcus, veillonella).
- Ornate (spirochetes, spirilla).
- Rod-shaped (rickettsia).
Among thick-walled gram-positive microorganisms, there are:
- Spherical (staphylococci, pneumococci, streptococci).
- Rod-shaped.
- Branched, filamentous organisms (actinomycetes).
- Club-shaped organisms (corynebacteria).
- Mycobacteria.
- Bifidobacteria.
Location and number of flagella
Morphology includes such a parameter as the location and number of flagella. According to this parameter, there are:
- Monotrichous (a single flagellum at the pole of their cell).
- Lophotrichous (bundle of flagella at the pole of their cell).
- Amphitrichous (two bundles of flagella at their poles).
- Peritrichous (a large number of flagella throughout the bacterium).
The presence of flagella is characteristic of intestinal microbes, vibrio cholerae, spirilla, alkaline-forming agents.
Cell wall colors
The color of bacteria is determined by the concentration of peptidoglycan. Organisms that are characterized by a high content of peptidoglycan in the cell walls (about 90%) have a blue-violet Gram color. These are Gram-positive bacteria.
All other bacteria, having from 5 to 20% peptidoglycan in the shell, acquire a pinkish color. Gram-negative bacteria are among them. The degree of peptidoglycan thickness in gram-positive organisms is several times higher than in gram-negative ones.
The cell walls of Gram-positive organisms also include polysaccharides, teichoic acids, and proteins. Gram-negative bacteria are covered by an outer membrane consisting of lipopolysaccharides and basal proteins.
Gram coloring allows you to classify prokaryotes into subcategories. Thick-walled microorganisms from the Gracilicutes department, protoplasts and spheroplasts with a defective cell wall are stained gram-negative. Thick-walled bacteria of the Firmicute type stain Gram-positive.
Classification by type of breathing
According to the type of breathing, there are:
- aerobic;
- anaerobic organisms.
Bacterial cells are capable of respiration, i.e., they oxidize organic compounds with oxygen, resulting in the formation of carbon dioxide, water and energy. These organisms are considered aerobic because they need oxygen. They live on the surface of water and land, in the air.
Many microorganisms exist without oxygen, that is, they do without respiration. These include bacteria involved in the process of decomposition of substances during humus. Such organisms are anaerobic. Respiration replaces fermentation - the decomposition of organic compounds without oxygen with energy production. During the fermentation of alcohol, an energy of 114 kJ (or 27 kilocalories) is formed, as a result of lactic acid, the energy is 94 kJ (or 18 kilocalories). Bacteria breathe in their lysosomes.
Feeding method
Classification of bacteria by types of nutrition:
- autotrophs;
- heterotrophs.
The former live in the air and use inorganic substances to produce organic ones. Autotrophs use solar energy (cyanobacteria) or the energy of inorganic compounds (sulfur bacteria, iron bacteria).
Enzyme classification
Enzymes play an important role in metabolic processes cells. They are divided into six groups:
- Oxireductases.
- Transferases.
- Hydrolases.
- Ligases.
- Liase.
- Isomerases.
The enzymes produced are located inside the cell (endoenzymes) or are excreted outside (exoenzymes). The second type of enzymes is involved in the entry of carbon and energy into the cell. Most of the enzymes from the group of hydrolases are classified as exoenzymes. A number of enzymes (collagenase, etc.) belong to the aggression enzymes. Individual enzymes are located in the cell walls. They perform a transport function, that is, they transfer substances into the cell.
Bacteria are non-nuclear unicellular microorganisms that are classified according to many parameters (respiration and nutrition methods, cell wall structure, shape, etc.). To date, science knows more than 10,000 species of bacteria, but presumably their number reaches a million.