Bacteria - general characteristic. Classification, structure, nutrition and role of bacteria in nature

People are trying to find new ways to protect themselves from their harmful influence. But there are also beneficial microorganisms: they promote the ripening of cream, the formation of nitrates for plants, decompose dead tissue, etc. Microorganisms live in water, soil, air, on the body of living organisms and inside them.

Shapes of bacteria

There are main 4 forms of bacteria, namely:

1. Micrococci – located separately or in irregular clusters. They are usually motionless.
2. Diplococci are arranged in pairs and can be surrounded by a capsule in the body.
3. Streptococci occur in chains.
4. Sarcines form clusters of cells shaped like packets.
5. Staphylococci. As a result of the division process, they do not diverge, but form clusters (clusters).

Rod-shaped types (bacilli) are distinguished by size, relative position and shape:

The bacterium has a complex structure:

• Wall cells protect a single-celled organism from external influences, give it a certain shape, provide nutrition and preserve its internal contents.
• Cytoplasmic membrane contains enzymes, participates in the process of reproduction and biosynthesis of components.
• Cytoplasm serves to perform vital functions. In many species, the cytoplasm contains DNA, ribosomes, various granules, and a colloidal phase.
• Nucleoid is the irregularly shaped nuclear region in which DNA is located.
• Capsule is a surface structure that makes the shell more durable and protects against damage and drying out. This mucous structure is more than 0.2 microns thick. With a smaller thickness it is called microcapsule. Sometimes around the shell there is slime, has no clear boundaries and is soluble in water.
• flagella are called surface structures that serve to move cells in a liquid environment or on a solid surface.
• Drank- thread-like formations, much thinner and fewer flagella. They come in various types, differ in purpose and structure. Pili are needed to attach the organism to the affected cell.
• Controversy. Sporulation occurs when unfavorable conditions arise and serves to adapt the species or preserve it.

Types of bacteria

We suggest considering the main types of bacteria:

Life activity

Nutrients enter the cell through its entire surface. Microorganisms have become widespread due to the existence of different types of nutrition. To live, they need a variety of elements: carbon, phosphorus, nitrogen, etc. The supply of nutrients is regulated using a membrane.

The type of nutrition is determined by how carbon and nitrogen are absorbed and by the type of energy source. Some of them can obtain these elements from the air and use solar energy, while others require substances of organic origin to exist. They all need vitamins and amino acids that can act as catalysts for reactions occurring in their body. The removal of substances from the cell occurs through the process of diffusion.

In many types of microorganisms, oxygen plays an important role in metabolism and respiration. As a result of respiration, energy is released, which they use to form organic compounds. But there are bacteria for which oxygen is lethal.

Reproduction occurs by dividing the cell into two parts. After it reaches a certain size, the separation process begins. The cell elongates and a transverse septum is formed in it. The resulting parts disperse, but some species remain connected and form clusters. Each of the newly formed parts feeds and grows as an independent organism. When placed in a favorable environment, the reproduction process occurs at high speed.

Microorganisms are able to decompose complex substances into simple ones, which can then be used again by plants. Therefore, bacteria are indispensable in the cycle of substances; without them, many important processes on Earth would be impossible.

Do you know?

Conclusion: Don't forget to wash your hands every time you come home after going outside. When you go to the toilet, also wash your hands with soap. A simple rule, but so important! Keep it clean and bacteria won't bother you!

To reinforce the material, we invite you to complete our exciting assignments. Good luck!

Task No. 1

Look carefully at the picture and tell me which of these cells is bacterial? Try to name the remaining cells without looking at the clues:

There are two types of taxonomy of biological objects: phylogenetic, or natural, which is based on the establishment of related (genetic, evolutionary) connections between organisms, and practical, or artificial, the purpose of which is to identify the degree of similarity between organisms in order to quickly identify them and establish their belonging to certain taxa.

Most classifications of bacteria are artificial. They are designed to identify a particular group of microorganisms of interest to researchers

The classification of all living things is based almost entirely on the morphological characteristics of the organisms.

The morphology of microorganisms studies the shape and structural features of cells, methods of reproduction and movement, etc. Morphological characteristics play a large role in the identification of microorganisms and their classification.

In bacteria, the classification has specific features due to the paucity of their morphological characteristics. Modern microbiology uses a set of characteristics for classification: morphological (cell shape, presence and location of flagella, method of reproduction, Gram staining, ability to form endospores ; physiological features (method of nutrition, energy production, composition of metabolic products, attitude to the effects of temperature, pH, oxygen and other factors ) ;cultural (character of growth on various nutrient media of the bacterial culture; on liquid media - the presence of film, turbidity, sediment; on solid media - the type of colonies and their features).

Currently, it is of great importance biochemical (genotypic) traits, i.e. features of the nucleotide composition of DNA. It is reliably known that individuals of the same species have the same composition of DNA bases, and in species belonging to the same genus, the nucleotide composition has similar values. Based on a combination of morphological, physiological, cultural and biochemical characteristics, bacteria can be classified as one species or another.

In recent years, the artificial classification of bacteria proposed by R. Murray in 1978 has gained recognition. According to this classification, the prokaryotic kingdom "Procaryotae" is divided into four divisions. The distribution of microorganisms into departments is based mainly on the presence or absence of cell walls and their structural features. For the microbiology of food production, two departments are important:

IN first department Firmicutes(“Firmus” - thick, solid) or “thick-skinned”, include all bacteria that are characterized by the structure of the cell wall according to the type Gram+ bacteria: all cocci, lactic acid bacteria (pediococcus - Pediococcus, lactobacilli - Lactobacillus, streptococci - Streptococcus and leuconostoc - Leuconostoc), rod-shaped spore-forming bacteria (Bacillus, Clostridium) and actinomycetes. Second department Gracilicutes(“Gracilus” - thin, graceful, “cutes” - skin) or “thin-skinned”, unites all bacteria that have a cell wall characteristic of Gram- bacteria: the genus Pseudomonas (some putrefactive bacteria, etc.), the genera Acetobacter and Gluconobacter (acetic acid bacteria), used in the production of vinegar, as well as pests of fermentation industries. Gram rods also include a large group - enterobacteria (bacteria of the intestinal group), incl. and the genus Escherichia. Some of the bacteria of the intestinal group constantly inhabit the intestines of humans and animals. Others are causative agents of infectious gastrointestinal diseases (dysentery, typhoid fever, paratyphoid fever) transmitted through food products, and food poisoning.

Control questions:

1. What are the main forms of bacteria in food production? 2. What are the main functions and chemical composition of the bacterial cell wall? 3. What functions does the cytoplasmic membrane perform in a bacterial cell? 4. What is the genetic apparatus of prokaryotes? 5.What is plasmids, In which bacteria are they present and what functions do they perform? 6.How do bacteria move? 7.What functions do endospores perform in bacteria, and under what conditions are they formed? 8.What is the basic principle of classification of bacteria?

Eukaryotes - microscopic fungi (filamentous fungi and yeast)

Filamentous fungi are characterized by a variety of methods and organs of reproduction. Differences in the structure of the mycelium and methods of reproduction are used to classify fungi. Fungal cells have branching threads - hyphae with apical growth and lateral branching, intertwining they form mycelium (mycelium).

Fungi reproduce vegetatively, asexually and sexually.

Vegetative propagation is carried out by separate sections of the mycelium, i.e. without the formation of specialized reproductive organs.

During asexual and sexual reproduction, specialized cells are formed - spores, with the help of which reproduction is carried out.

The formation of spores during asexual reproduction is preceded by mitotic nuclear division , in which two daughter nuclei are formed with a set of chromosomes identical to the set of the parent cell.

During asexual reproduction, spores are formed on special fruits
bearing hyphae of aerial mycelium, externally different from vegetative
tive gif.

In lower fungi, spores are formed inside special cells - sporangia, they are called sporangiospores . In higher fungi, spores are formed exogenously (externally) on the hyphae of aerial mycelium and are called conidia .

Fig. 12. Organs of vegetative and asexual reproduction of fungi: a - oidia; b - chlamydospores; c - sporangiospores; d – conidia

The formation of spores during sexual reproduction is preceded by fusion ( copulation) two germ cells – gametes and their nuclei. A diploid cell is formed - zygote, containing a double set of chromosomes. Then follows the process of reduction division - meiosis, accompanied by a redistribution of paternal and maternal characteristics, leading to a decrease in the number of chromosomes to the original and an increase in the diversity of species. As a result, specialized reproductive organs are formed. The development of these organs and the forms of the sexual process in fungi are diverse.

Classification of mushrooms. The division of fungi into classes is based on the use of a set of characteristics, the leading of which are the composition of the cell wall, types of sexual and asexual reproduction. According to modern classification, all mushrooms are divided into the following classes:

Class Chytridiomycetes(Chytridiomycetes)

Synchytrium- is the causative agent of potato cancer.

Class Zygomycetes(Zygomycetes): Genus Mucor - cause food spoilage by forming fluffy deposits.

Fig. 13. Genus Mucor Fig. 14. Genus Rhizopus

Fungi of the genus Rhizopus cause so-called “soft rot” of berries, fruits and vegetables. Mucor fungi produce organic acids and enzymes and are capable of causing weak alcoholic fermentation.

Class Ascomycetes(Ascomycetes): Ascomycetes include the important Aspergillus and Penicillium fungi.

Fig.15 . Aspergillus niger Fig.16 . Penicillium chrysogenum

Marsupial fungi are widespread in nature. Many of them are the causative agents of spoilage of fruits and vegetables (especially during storage - various rots) and many food products. Some of them cause damage to industrial products and materials (textiles, rubber, cellophane, plastics, etc.). Some representatives of Aspergillus and Penicillium fungi are used in industry. Thus, some penicilliums are producers of antibiotics - penicillin, cephalosporin, griseofulvin, citrinin, etc. Penicillium roqueforti, Penicillium camemberti used in the production of Roquefort and Camembert cheeses; Aspergillus niger – for industrial production of citric acid; A. oryzae, A. awamori - for obtaining enzyme preparations. Some Aspergillus are pathogenic for humans and animals, causing damage to the respiratory tract (otomycosis, aspergillosis and emphysema), skin (dermatomycosis), and oral mucosa.

In the last half century, scientists have paid special attention to secondary metabolites of filamentous fungi that develop on food raw materials of plant and animal origin and on food products and feeds - mycotoxins . Approximately 60–75% of fungi that cause spoilage of food and animal feed are toxic and highly toxic. Eating moldy food is extremely dangerous to human and animal health. Numerous studies have established the hepatotropic, carcinogenic and mutagenic effect on the human and animal body of aflatoxins, ochratoxins, patulin, rubratoxin, etc., secreted by fungi Aspergillus flavus, A. ochraceus, Penicillium veridatum, P.islandicum, P. rubrum, P. expansum etc. All mycotoxins are dangerous even in small quantities and are difficult to degrade (destruct).

Fig. 17. Claviceps (ergot) Fig. 18. Monilia (monilia)

Fruit-bearing ascomycetes also include truffles and morels, the fruiting bodies of which are eaten, as well as strings, which are considered conditionally edible, since some of their species are poisonous.

Fig. 19: a – morel cap; b - autumn line.

Fig.20. tinder mushroom

This ability is much more pronounced in them than in higher plants, lichens and other organisms. This is why you should not collect mushrooms in areas contaminated with industrial waste. The accumulation of these elements causes a number of irreversible rearrangements in the biochemical apparatus of fungi. This phenomenon has so far been little studied and therefore poses a threat to human health.

Class Deuteromycetes(Deuteromycetes): They do not have sexual reproduction; they reproduce only asexually, mainly by conidia, which, like conidiophores, have a wide variety of shapes, appearances and colors. Some species do not develop specialized reproductive organs, and they reproduce by pieces of mycelium.

Fig.21. Genus Fusarium (Fusarium) Fig. 22. Genus Botrytis

Genus Botrytis the fungus causes black rot of sugar beets; developing on grapes, fruits and berries, it softens tissues that become watery. Produces the enzymes pectinase, ceplulase, invertase, etc.

Kinds Alternaria widely distributed in soil and plant debris. The fungus causes Alternaria disease in many agricultural plants. Black sunken spots form on food products (black dry rot of carrots, black spot of cabbage). When the affected areas of the leaf fall out, holes are formed.

Genus Geotrichum develops on the surface of fermented milk products, cheeses, pickled vegetables, compressed yeast, walls of equipment, and damp rooms. Some species of the genus Geotrichum cause spoilage of poorly dried hops.

Genus Monilia are active causative agents of spoilage of fruits, which turn into so-called “mummies”. Representatives of this genus, belonging to the class Deuteromycetes, exist in the conidial stage.

Genus Cladosporium. Mushrooms are often found during refrigerated storage on various food products in the form of velvety dark olive (to black) spots.

Genus Helminthosporium Diseases of cereals caused by fungi of this genus are called helminthosporioses. Some species of this genus are saprophytes and develop on roots, leaves, dry branches, stems, stems of wood and herbaceous plants.

Rice. 23. Rod Helminthosporium

Yeast are unicellular fungal, nonmotile organisms that do not have true mycelium. They live mainly on plants where there are sugary substances that they ferment (nectar of flowers, juicy fruits, berries, especially overripe and damaged ones, leaves, birch trunks during sap and oak during sap, soil). Yeast cells are oval, cylindrical, ovoid, lemon-shaped, flask-shaped, triangular, arrow-shaped and crescent-shaped. Some types of yeast, along with round and oval cells, can form elongated and pseudomycelium. Yeast cells are much larger than bacterial cells.

Like all fungi, yeast are non-motile organisms. Yeast has a rather complex structural organization, typical of eukaryotic organisms.

Yeast reproduces vegetatively and by spores produced asexually and sexually. The method of reproduction is an important characteristic for the classification of yeast. The most common method of vegetative propagation is budding.

If, during budding, the newly emerging cells are not separated from each other, then pseudomycelium is formed. Reproduction by division, characteristic of cylindrical yeasts, is less common. In lemon-shaped yeast, the so-called budding division is observed, in which a bud is formed on a wide base, the process ends with the appearance of a clearly visible septum in the area of ​​the isthmus.

During sexual reproduction, their appearance is preceded by the fusion of cells and the subsequent union of nuclei; during asexual reproduction, the preliminary fusion of cells and nuclei does not occur. Sexual reproduction of most yeasts involves the formation of asci (bags) and ascospores.

The formation of ascospores is preceded by copulation (fusion of the contents of two cells and their nuclei). A zygote is formed, in which spores are then formed: the nucleus divides by meiosis, the cytoplasm is compacted around the new nuclei, and they are covered with a dense shell. Such yeasts belong to the class of ascomycetes. Ascospores can only form in young cells on a complete nutrient medium and transferred to conditions of starvation, poor supply of oxygen and moisture. In various types of yeast, the ascus produces

2 - 4, and sometimes 8 disputes. During sporulation, metabolism and cell activity are slowed down. This condition ensures their survival in conditions unfavorable for vegetative propagation.

Ascospores are resistant to high temperatures and drying, but they are less thermostable than bacterial spores and die at a temperature of 60°C. Under conditions favorable for vegetative development, on a fresh nutrient medium, spores germinate and again reproduce vegetatively. Since yeasts are essentially single-celled, non-mycelial fungi, they are included in the classification of fungi. They are divided into three classes of mushrooms - Ascomycetes, Basidiomycetes and Deuteromycetes .

Ascomycete yeast include approximately 2/3 of yeast. Among them, Saccharomycetes are of greatest practical importance, uniting more than half of the known genera of yeast. A particularly important role belongs to Saccharomyces cerevisiae (large oval cells) in the production of ethyl alcohol, beer, kvass and in bakery and Saccharomyces ellpsoideus (large elliptical cells) - they are used mainly in winemaking.

Fig.25. Saccharomyces cerevisiae

Yeast class Deuteromycetes childbirth matters most Candida, Torulopsis and Rhodotorula. Candida have an elongated shape of cells, the combinations of which form a primitive pseudomycelium. Many of them do not cause alcoholic fermentation and are pests in fermentation industries (for example, Candida mycoderma ). Other representatives of the genus Candida They are pests in yeast production and reduce the quality of baker's yeast, as they are a weakly fermenting species. Some of them cause spoilage of pickled vegetables, soft drinks and a number of other drinks and products. Among these yeasts there are pathogenic species that cause candidiasis, affecting the mucous membranes of the oral cavity, nasopharynx and other human organs. Various types of yeast genus Candida are used to obtain feed protein and protein-vitamin concentrates (PVC).

Yeast genus Torulopsis are capable of causing weak alcoholic fermentation and are used in the production of kefir and kumiss. Some are used for industrial production of feed protein.

Yeast genus Rhodotorula are used for the industrial production of feed protein-vitamin concentrates, which serve as a source of fat-soluble vitamin A for animals. Other members of this genus accumulate a lot of lipids in cells and are used in the microbiological industry as lipid producers.

Viruses

Fig.26. Bacteriophage: A – phage model; B – phage that has injected its DNA into the cell

In medicine, bacteriophages are used to treat certain diseases, such as dysentery.

Control questions:

1 . What are the morphological features and methods of reproduction of filamentous fungi? 2. What are the structural features and reproduction of yeast? 3. Explain the basic principles of classification of prokaryotes and eukaryotes. 4. Name the main representatives of individual classes of eukaryotes and their practical significance. 5. Explain the structure and practical significance of viruses and phages.

Metabolism in microorganisms is extremely diverse. This is due to the ability of microorganisms to use a wide range of organic and mineral compounds for metabolism. This ability is due to the presence of a wide variety of enzymes in microorganisms. The activity of enzymes is influenced by temperature, pH and other environmental factors - exposure to environmental chemicals, radiant energy, etc. Physiological processes occurring in the cells of microorganisms almost completely depend on the activity of enzymes, therefore any factor acting on the enzyme will also affect metabolism of microorganisms.

Each type of microorganism is characterized by a certain set of enzymes that are constantly present in the cell (the so-called constitutive enzymes). At the same time, some enzymes are synthesized by the cell only when the appropriate substrate appears in the environment. Such enzymes are called inductive.

Based on the nature of their action, enzymes are divided into exoenzymes, released by the cell into the environment, and endoenzymes. firmly associated with cellular structures (mitochondria, cytoplasmic membrane and mesosomes) and act inside the cell. Both play an important role in the metabolism of microorganisms. Exoenzymes (usually hydrolases) catalyze reactions outside the cell. Endoenzymes include oxidoreductases (redox enzymes), transferases (transfer enzymes), etc., which play an important role in energy metabolism.

Constructive metabolism consists in the biosynthesis of the main cellular components from the substances of the nutrient medium that enter the cell. Constructive metabolism is aimed at the synthesis of four main types of biopolymers: proteins, nucleic acids, polysaccharides and lipids. Synthesis proceeds as a series of sequential reactions with the formation of a variety of metabolic intermediate products. In addition, the levels of development of the biosynthetic abilities of microorganisms are different. That is why microorganisms differ sharply from each other in their nutritional needs. Regardless of their needs, the nutrient medium must contain all the elements that are present in the cells of microorganisms. In relation to carbon sources, all microorganisms are divided into two large groups: autotrophs And heterotrophs . Accordingly, the type of nutrition of these microorganisms is called either autotrophic or heterotrophic. Microorganisms that use an inorganic source of carbon (CO 2) for the biosynthesis of cell substances are called autotrophs. Microorganisms that cannot use CO 2 as the only carbon source and require organic compounds are called heterotrophs. Most microorganisms are heterotrophs.

Many heterotrophic microorganisms for the synthesis of cell substances use mainly carbohydrates and alcohols as a carbon source, but in addition they can use lipids, proteins, amino acids (their carbon skeleton) and much less often organic acids. In relation to the source of nitrogen, microorganisms are divided into aminoautotrophs and aminoheterotrophs. Aminoautotrophs absorb nitrogen from mineral compounds (nitrates, nitrites, ammonium salts, etc.) Aminoheterotrophs need ready-made organic nitrogen-containing compounds (proteins, amino acids, purines, pyrimidines), which they use simultaneously as a source of carbon and nitrogen.

Saprophytes feed on organic matter from dead animals and plants. These include putrefactive bacteria, filamentous fungi, actinomycetes, yeast, bacteria that cause fermentation processes, etc.

Supply of water and nutrients from the environment and the release of metabolic products from microorganisms occurs through the entire surface of the cells. Substances in the nutrient medium must be soluble in water or lipids, since they can penetrate into the microbial cell only in dissolved form; Metabolic products are also removed from the cell in a dissolved state. Insoluble complex organic substances (proteins, polysaccharides, fats, etc.) of the nutrient medium are first subjected to splitting outside the cell into lower molecular weight compounds that are soluble in water (amino acids, monosaccharides, organic acids, etc.), with the help of hydrolytic agents released into the external environment by microorganisms. enzymes.

Molecules of water, some gases O 2, H 2, N 2, some ions, the concentration of which in the external environment is higher than in the cell, move through the CPM into the cell by passive diffusion. Passive transfer of substances occurs until the concentration of substances on both sides of the CPM is equalized. Water is the main substance that penetrates the cell through passive diffusion.

Only those nutrients for which there are appropriate carriers in the CPM enter the cell from the nutrient medium, and this manifests the selective permeability of the CPM.

Permeases have strict substrate specificity, i.e. each of them transports only a certain substance. The transporter interacts with a substance on the outside of the CPM, and this complex diffuses through the CPM to the inside of the CPM, the complex disintegrates and then the substance is transferred into the cytoplasm. After this, the carriers “capture” certain metabolic products, carry them out of the cell, and the process repeats. Thus, only those substances for which there are appropriate carriers in the CPM enter the cell from the nutrient medium, and this manifests the selective permeability of the CPM.

With the help of carriers, the transfer of dissolved substances in the nutrient medium is carried out through facilitated diffusion and active transport.

Facilitated diffusion occurs along a concentration gradient, like passive diffusion, it also occurs without energy consumption, but at a higher speed.

Figure 27. Transport of substances across the cytoplasmic membrane:

a - cytoplasm: b - membrane; c- environment: p – carrier

Active transport substances goes against the concentration gradient, i.e. from lower to higher concentrations, which is necessarily accompanied by energy expenditure. Once inside the cell, the substance is released from the carrier, also with the expenditure of energy. With active transport, the rate of entry of a substance into the cell reaches a maximum even at a low concentration in the nutrient medium, and the concentration of this substance in the cell can significantly exceed its concentration in the nutrient medium.

Prokaryotes and eukaryotes differ in transport mechanisms - in prokaryotes, selective intake of nutrients occurs by active transport, in eukaryotes - by facilitated diffusion. The removal of metabolic products from microbial cells is most often carried out by facilitated diffusion.

1.5. Modern classification of bacteria In modern taxonomy of bacteria, a situation has developed that is also characteristic of the classification of other organisms: successes have been achieved in creating a phylogenetic classification system that reflects the main directions of evolutionary development and the kinship of representatives of certain taxa, but artificial phenomena retain their importance - typical classifications, more convenient for identifying microorganisms. At present, there is no detailed evolutionary system of prokaryotes and, most likely, the solution to this problem is a matter of the near future. The peculiarities of prokaryotes in the field of morphological, physiological-biochemical, and genetic organization indicate the inapplicability to them of well-developed principles used in constructing a system of higher organisms. Without dwelling on the historical aspects of the problem of bacterial taxonomy, it should be noted that the most acceptable phylogenetic system for classifying prokaryotes is the system based on comparison of the nucleotide sequence in 16S rRNA. This system is the basis for the 2nd edition of the multi-volume encyclopedia of prokaryotes - Bergey's Manual of Systematic Bacteriology, the first volume of which was published in 2001. In this work, all prokaryotes are divided into 26 phylogenetic “branches” (groups ) based on the structure of their 16S rRNA; 23 “branches” are represented by eubacteria, and three by archaebacteria. It should be emphasized that a large number of these phylogenetic groups contain species of prokaryotes that have not been isolated as pure cultures and therefore have not yet been studied in detail. For representatives of these species, only nucleotide sequences in 16S rRNA are currently known. Of the 23 groups of eubacteria, two phylogenetic groups are represented by gram-positive bacteria, the remaining groups are gram-negative. Gram-negative bacteria consist of a large group of Proteobacteria and 20 groups of other bacteria that have this type of cell wall. A brief description of Proteobacteria, to which the mitochondria and chloroplasts of most eukaryotes are most similar in 16S-rRNA composition, is given in Table. 2. Proteobacteria are a very heterogeneous group of gram-negative bacteria in morphological, physiological and biochemical terms. Representatives of this group are characterized by all types of energy metabolism and nutrition. The cells of most species of Proteobacteria have a rod-shaped, spherical or vibrioid shape and reproduce mainly by binary fission, but some species are characterized by budding and the formation of fruiting bodies in a complex cell cycle. This group contains both motile bacteria due to flagella and immobile bacteria. With respect to molecular oxygen, Proteobacteria are obligate aerobes, obligate and facultative anaerobes. The Proteobacteria group is divided into five subgroups based on differences in 16S rRNA: alpha, beta, gamma, delta and epsilon. In addition to prosebacteria, the following main groups of eubacteria include: hydrogen thermophiles, green thread bacteria, green sulfuric bacteria, cyanobacteria, spirochetes, cytopharages, bacteroids, chlamydia, planktomycetes, deinococci, chloroflexus, fuzobacteria, fibrobacteria, and thermal fiberias, and thermal bacteria and other phylogenetic groups gram-positive bacteria – Actinobacteria and Firmicutes. The Actinobacteria group (“actinomycete branch”) is represented by the following genera of bacteria that have a high content of GC pairs in DNA: Geodermatophilus, Frankia, Streptomyces, Arthrobacter, Micrococcus, Actinomyces, Bifidobacterium, Propionibacterium, Actinoplanes, Nocardia, Rhodococcus, Corynebacterium, Mycobacterium. The Firmicutes group (“clostridial branch” - mainly gram-positive bacteria with a low content of GC pairs in DNA) consists of the following genera: Clostridium, Lactococcus, Pediococcus, Streptococcus, Enterococcus, Leuconostoc, Listeria, Caryophanon, Staphylococcus, Sarcina, Sporosarcina, Bacillus, Desulfotomaculum, Heliobacterium, Mycoplasma, Ureaplasma, etc. Archaebacteria include three phylogenetic groups: Crenarchaeota, Euryarchaeota and Korarchaeota. The Crenarchaeota group consists of extremely thermophilic bacteria, most of whose representatives metabolize sulfur, while some reduce iron and molybdenum ions. The Euryarchaeota group includes obligate anaerobic methanogenic archaebacteria, as well as extreme thermophiles and halophiles. The Korarchaeota group is formed by archaebacteria that live in hot sulfur springs. To date, none of the representatives of this group (possessing a similar 16S rRNA) has been isolated as a pure culture, so their phenotypic characteristics have not been sufficiently studied. Concluding the consideration of the phylogenetic branches of prokaryotes, it should be noted that the proposed phylogenetic system, based on the study of nucleotide sequences of only one ribosomal RNA gene, is nothing more than one of the technically convenient and developed systems for ordering numerous organisms for the purpose of their identification, therefore, construct logically a correct taxonomy of bacteria only taking this feature into account is not possible. The most recognized and used phenotypic classification of bacteria is the classification presented in the ninth edition of Bergey's Key to Bacteria. In this publication, bacteria, based on the structure of the boundary layer of cells, are divided into four main categories (divisions): 1) Gracilicutes (from the Latin cutes - skin, gracilis - thin) - gram-negative eubacteria with cell walls; 2) Firmicutes (from Latin firmus – strong) – gram-positive eubacteria with cell walls; 3) Tenericutes (from Latin tener - soft, tender) - eubacteria lacking cell walls; 4) Mendosicutes (from the Latin mendosus - erroneous) - archaebacteria, the cell walls of which differ from similar structures of other prokaryotes. The department Gracilicutes includes bacteria of various morphologies with a Gram-negative cell wall. Reproduction occurs mainly by binary fission; some bacteria reproduce by budding. Endospores do not form. Most are motile: all types of bacterial movement are found – with the help of flagella, sliding, bending. The department includes aerobic, anaerobic and facultative anaerobic bacteria; phototrophic and chemotrophic bacteria. The department is divided into three classes: Scotobacteria, Oxyphotobacteria, Anoxyphotobacteria. The class Scotobacteria includes gram-negative bacteria that do not use light energy for metabolic purposes, but receive it only as a result of redox reactions. The name of the class comes from the Greek. sсotos – darkness. This is the largest class of bacteria. The class Anoxyphotobacteria includes purple bacteria, green bacteria and heliobacteria, which carry out anoxygenic photosynthesis (without the release of molecular oxygen). The Oxyphotobacteria class is represented by cyanobacteria and prochlorophytes that carry out oxygenic photosynthesis (with the release of molecular oxygen). This type of photosynthesis is similar to the photosynthesis that occurs in plants. The division Firmicutes includes bacteria with a gram-positive cell wall. Cells can have different shapes: rods, cocci, filamentous, branching. Some representatives form endospores. Most of them are motionless; motile forms have peritrichous flagellation. The department includes aerobic, anaerobic and facultative anaerobic bacteria. The department consists of two classes: Firmibacteria, Thallobacteria. The class Firmibacteria includes a large number of “non-branching” gram-positive bacteria. The Thallobacteria class includes bacteria whose cells are capable of branching. The Tenericutes division is represented by bacteria that do not have a cell wall. Due to the absence of a cell wall, the shape of the cells is not constant: in a pure culture of one species, coccoid, rod-shaped, filamentous, pear-shaped, disc-shaped and other cells are simultaneously present. Reproduction of bacteria included in this section occurs by binary fission and budding. Gram stain is negative. The formation of small colonies growing into agar is characteristic. May be saprophytic, parasitic or pathogenic. The department consists of one class Mollicutes (mycoplasma). The division Mendosicutes is formed by bacteria with a rigid cell wall, but not containing the peptidoglycan murein. Most representatives are strict anaerobes, many of which have flagella. Species are characterized by ecological and metabolic diversity and the ability to live in extreme conditions. The department consists of one class – Archaebacteria. Within four divisions (main categories), 35 groups (or sections) of bacteria have been identified, which will be characterized to a greater or lesser extent in subsequent chapters. The following groups belong to the department Gracilicutes. Group 1. Spirochetes. Group 2. Aerobic (or microaerophilic), motile, spiral-shaped (or vibrioid) gram-negative bacteria. Group 3. Non-motile or rarely motile gram-negative curved bacteria. Group 4. Gram-negative aerobic (or microaerophilic) rods and cocci. Group 5. Facultative aerobic gram-negative rods. Group 6. Gram-negative anaerobic straight, curved or spiral rods. Group 7. Bacteria that carry out the dissimilatory reduction of sulfur or sulfate. Group 8. Anaerobic gram-negative cocci. Group 9. Rickettsia and chlamydia. Group 10. Anoxygenic phototrophic bacteria. Group 11. Oxygenic phototrophic bacteria. Group 12. Aerobic chemolithotrophic bacteria and related organisms. Group 13. Budding and (or) outgrowth-forming bacteria. Group 14. Bacteria with covers. Group 15. Non-photosynthetic gliding bacteria that do not form fruiting bodies. Group 16. Sliding bacteria that form fruiting bodies. The division Firmicutes includes: Group 17. Gram-positive cocci. Group 18. Gram-positive rods and cocci forming endospores. Group 19. Gram-positive rods of regular shape, not forming spores. Group 20. Gram-positive rods of irregular shape that do not form spores. Group 21. Mycobacteria. Groups 22–29. Actinomycetes. The department Tenericutes belongs to: Group 30. Mycoplasmas. The department Mendosicutes includes: Group 31. Methanogens. Group 32. Sulfate-reducing archaebacteria. Group 33. Extremely halophilic archaebacteria (halobacteria). Group 34. Archaebacteria lacking a cell wall. Group 35. Extremely thermophilic and hyperthermophilic archaebacteria that metabolize sulfur. In conclusion, it should be emphasized that the majority of microorganisms existing in natural communities must still be isolated into pure cultures. It is believed that at present only 0.1% of the total microbial diversity can be cultivated, and the remaining representatives of bacteria cannot be grown and identified, although about 5 thousand species of prokaryotes have already been isolated and described in pure culture.

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

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

Classification of bacteria by Gram stain

Form: cocci, rods or spirals.

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

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

Demandingness: Some bacteria require special culture conditions to grow.

Classification of bacteria in relation to oxygen

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

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

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

Medically significant species of bacteria

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

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

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

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

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

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

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

Bacteria are prokaryotic microorganisms with a cellular structure. Their sizes range from 0.1 to 30 microns. Germs 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 takes into account 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:

Coca - micro-, diplo-, strepto-, staphylococci, as well as sarcina;

Rod-shaped - monobacteria, diplobacteria and streptobacteria;

The convoluted species are vibrios and spirochetes.

Bergey's determinant systematizes all known bacteria according to the most widely used principles of bacterial identification in practical bacteriology, based on differences in the structure of the cell wall and the relationship to Gram staining. 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 identifies four main categories of bacteria -

Gracillicutes [from Lat. gracilis, graceful, thin, + cutis, skin] - species with a thin cell wall, staining gram negative;

firmicutes [from lat. flrmus, strong, + cutis, skin] - bacteria with a thick cell wall, staining gram-positive;

Tenericutes [from Lat. tener, tender, + cutis, skin] - bacteria lacking a cell wall(mycoplasmas and other representatives of the class Mollicutes)

Mendosicutes [from Lat. mendosus, irregular, + cutis, skin] - archaebacteria (methane- and sulfate-reducing, halophilic, thermophilic and archaebacteria lacking a cell wall).

Group 2 of the Bergey determinant. Aerobic and microaerophilic motile convoluted and curved gram-negative bacteria. Species pathogenic to humans are included in the genera Campylobacter and Helicobacters Spirillum.

Group 3 of the Bergey determinant. Non-motile (rarely motile) gram-negative bacteria. Does not contain pathogenic species.

Group 4 of the Bergey determinant. Gram-negative aerobic and microaerophilic rods and cocci. Species pathogenic to humans are included in the families Legionellaceae, Neisseriaceae and Pseudomonada-ceae; the group also includes pathogenic and opportunistic bacteria of the genera Acinetobacter, Afipia, Alcaligenes, Bordetella, Brucella, Flavobacterium, Francisella, Kingella and Moraxella.

Group 5 of the Bergey determinant. Facultatively 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 the Bergey 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 the Bergey determinant. Bacteria performing dissimilatory reduction of sulfate or sulfur Does not include pathogenic species.

Group 8 of the Bergey determinant. Anaerobic gram-negative cocci. Includes opportunistic bacteria of the genus Veillonella.

Group 9 of the Bergey determinant. Rickettsia and chlamydia. Three families - Rickettsiaceae, Bartonellaceae and Chlamydiaceae, each of which contains species pathogenic to humans.

Groups 10 and 11 of Bergey's determinant include anoxy- and oxygenic phototrophic bacteria that are not pathogenic to humans.

Group 12 of the Bergey determinant. Aerobic chemolithotrophic bacteria and related organisms. Combines iron-sulphur- and manganese-oxidizing and nitrifying bacteria that do not cause damage to humans.

Groups 13 and 14 of Bergey's determinant include budding and/or protruding bacteria and sheath-forming bacteria. They are represented by free-living species that are not pathogenic to humans;

Groups 15 and 16 of Bergey's determinant combine gliding bacteria that do not form fruiting bodies and those that form them. The groups do not include species pathogenic to humans.

Group 17 of the Bergey determinant. Gram-positive cocci. Includes opportunistic species of the genera Enterococcus Leuconostoc, Peptococcus, Peptostreptococcus, Sarcina, Staphylococcus, Stomatococcus, Streptococcus.

Group 18 of the Bergey determinant. Spore-forming gram-positive rods and cocci. Includes pathogenic and opportunistic bacilli of the genera Clostridium and Bacillus.

Group 19 of the Bergey determinant. Spore-forming gram-positive rods of regular shape. Including opportunistic species of the genera Erysipelothrix and Listeria.

Group 20 of the Bergey determinant. Spore-forming gram-positive rods of irregular shape. The group includes pathogenic and opportunistic species of the genera Actinomyces, Corynebacterium Gardnerella, Mobiluncus, etc.

Group 21 of the Bergey 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 the Bergey determinant. Mycoplasmas. Species included in the genus Acholeplasma, Mycoplasma and Ureaplasma are pathogenic to humans.

The remaining groups of Bergey's determinant - methanogenic bacteria (31), sulfate-reducing bacteria (32 extremely halophilic aerobic archaebacteria (33), archaebacteria lacking cell walls (34), extreme thermophiles and hyperthermophiles that metabolize sulfur (35) - do not contain species pathogenic to humans.