Microorganisms are a large collective group, within which representatives may differ in cellular organization, morphology and metabolic capabilities, but are united by microscopic sizes. Therefore, the term "microorganism" has no taxonomic meaning. Representatives of the world of microbes belong to a variety of taxonomic groups, the other members of which can be multicellular organisms, sometimes gigantic. For example, lower mold fungi are related cap mushrooms, and microalgae are combined with such large specimens as kelp. Microorganisms are the largest group in terms of the number of representatives and its members are ubiquitous. Microorganisms have all known types of metabolism.

Ways to classify microorganisms

The accumulation of vast factual material required the introduction of rules for describing objects and distributing them into groups. For the possibility of comparing the results obtained by different researchers, and the convenience of work, it became necessary to classify microorganisms. Classification refers to the assignment of a specific biological object to a certain homogeneity group (taxon) according to the totality of its inherent features.

The relationship of subordination and the relationship of taxa of different levels is studied by systematics . In the modern classification of microorganisms, the following hierarchy of taxa is adopted: domain, phylum, class, order, family, genus, species. The species is the basic taxonomic unit. Microbiologists use a binomial system for designating an object (nomenclature), including generic and specific names, for example, Escherichia coli, Saccharomyces cerevisiae, Pseudomonas aeruginosa etc. In some cases, the use of historically established Russian-language names (E. coli, baker's yeast, Pseudomonas aeruginosa) is allowed.

For classification, it is important to agree on a set of criteria that will be decisive when combining objects into a group. Most microorganisms have an extremely simple and universal structure; therefore, morphological descriptions are not enough to divide them into taxa. Researchers were forced to use the functional characteristics of microorganisms, i.e. note the peculiarities of their metabolism. At the same time, depending on the approach, the signs could have unequal significance (some were mandatory for placement in this group, while others could vary).

At present, it is impossible to classify a microbiological object without examining the totality of morphophysiological, biochemical, and molecular biological data. When determining an unknown microorganism (identification), the following properties are examined:

  1. Cell cytology (first of all, assignment to pro- or eukaryotes);
  2. Morphology of cells and colonies (on certain media and under certain conditions);
  3. Cultural characteristics (character of growth on solid and liquid media);
  4. Physiological properties (ability to use various substrates, relation to temperature, aeration, pH, etc.);
  5. Biochemical properties (presence of certain metabolic pathways);
  6. Molecular biological properties (nucleotide sequence of 16S rRNA, content of GC-AT pairs in mol.%, the possibility of hybridization of nucleic acids with the material of typical strains);
  7. Chemotaxonomic properties (chemical composition of various compounds and structures, for example, the spectrum of fatty and teichoic acids in actinobacteria, mycolic acids in nocardia, mycobacteria, corynebacteria);
  8. Serological properties based on antigen-antibody reactions (especially for pathogens);
  9. Sensitivity to specific phages (phage typing).

Sometimes the presence of extrachromosomal elements in a microorganism, including silent (cryptic) plasmids, is noted. It should be remembered that plasmids can be easily lost.

When identifying prokaryotic microorganisms, modern researchers rely on the instructions of the Bergey's Manual of Systematic Bacteriology and use the Bergey key.

Currently, there are several main ways to classify living objects, including microorganisms.

Formal numerical classification considers all signs of an organism to be of equal importance. The criteria to be taken into account must be alternative, i.e. present (+) or (-) absent from a particular object. The accuracy of placing it in this group will depend on the completeness of the study of the organism. To quantify the degree of similarity and difference between objects, special computer programs have been developed that compare organisms according to a set of studied traits. Similar organisms are combined into clusters.

For morphophysiological classification, it is necessary to study the totality of morphological features and characteristics of the metabolism of organisms. At the same time, the different significance of the applied criteria is taken into account: some properties are considered mandatory, significant for the object, while others may be present to varying degrees or completely absent. To place microorganisms in a group and give them a name, first determine the type of cellular organization, describe the morphology of cells and colonies, as well as the nature of growth on certain media and under certain conditions. The functional characteristics of the object include the possibility of using various nutrients, the relationship to the physical and chemical factors of the environment, as well as the identification of ways to obtain energy and reactions of constructive exchange. Some microorganisms require chemotaxonomic studies. Pathogenic microorganisms are usually subjected to serodiagnosis. The results of all these tests are used when working with the determinant. At present, to identify prokaryotic microorganisms, researchers use a determinant named after the American bacteriologist Burgee, who in 1923 proposed the basis for such a classification.

Molecular genetic classification involves the analysis of the molecular structure of important biopolymers. Such a molecule must be conserved and meaningful to the underlying life process. University of Illinois professor Carl Vöz suggested taking prokaryotic 16S ribosomal RNA (18S rRNA for eukaryotic organisms) as a basis. This molecule is part of the ribosomes, which in all living beings are responsible for the most important life process - protein synthesis. The apparatus of protein synthesis changes slightly over time, since any significant disturbance can lead to cell death. Therefore, in rRNA molecules different organisms most nucleotides are unchanged, and the part that changes in the course of evolution is unique to a particular organism. 16S rRNA consists of 1500 nucleotides, of which 900 are conserved; it possesses sufficiently large, but not excessive information and can be considered a kind of biological genetic "chronometer". Comparing with special computer programs nucleotide sequences of this molecule in different organisms, it is possible to obtain similarity groups of biological objects, reflecting their family ties and evolutionary development. Based on many comparisons, a phylogenetic tree was built, where all representatives of the living world are divided into three large domains (empires, superkingdoms): Bacteria, Archaea and Eukarya. The Bacteria and Archaea domains contain only prokaryotic organisms, while the Eukarya domain includes all eukaryotes, both unicellular and multicellular, including humans. At the same time, it was proved that mitochondria and chloroplasts have a prokaryotic symbiotic origin. Researchers send the nucleotide sequences of the studied organisms to the worldwide computer genebank, the data of which are intended for comparison with the sequences of each newly isolated organism.

Currently, to identify a specific microorganism, its pure culture is first isolated and the 16S rRNA nucleotide sequence is analyzed. It allows you to determine the place of the microorganism on the phylogenetic tree, and then the determination of the species name is carried out by traditional methods. microbiological methods. At the same time, 90% of matches indicate belonging to a certain genus, 97% - to a certain species. To clarify the taxonomic affiliation, DNA-DNA hybridization is carried out, which gives > 30% coincidence within the genus and > 70% within the species.

For a clearer differentiation of microorganisms at the level of genus and species, it is proposed to use polyphyletic (polyphase) taxonomy, when, along with the determination of nucleotide sequences, information is used different levels up to ecological. At the same time, a preliminary search for groups of similar strains and the determination of the phylogenetic positions of these groups are carried out, differences between the groups and their nearest neighbors are recorded, and data are collected to differentiate the groups.

Main groups of eukaryotic microorganisms

IN Eukarya domain there are three groups containing microscopic objects. These are algae, protozoa and fungi.

Seaweed("growing in water") are unicellular, colonial or multicellular phototrophs that carry out oxygenic photosynthesis. The molecular genetic classification of algae is under development, therefore, for practical purposes, algae are classified according to the composition of pigments, reserve substances, the structure of the cell wall, the presence of mobility and the method of reproduction. Microbiological objects are traditionally considered unicellular representatives of dinoflagellates, diatoms, euglenoids and green algae, as well as their colorless forms that grow in the dark and have lost pigments. All algae form chlorophyll A and various forms of carotenoids, and representatives of the groups differ in their ability to synthesize other forms of chlorophylls and phycobilins. Cell staining in different colors: green, brown, red, golden, - depends on the combination of pigments in a particular species. Diatoms are unicellular planktonic forms that have a characteristic cell wall in the form of a silicon bivalve shell. Some representatives can move by sliding. They reproduce both asexually and sexually. Unicellular euglenoid algae live in freshwater bodies and move with the help of flagella. They lack a cell wall. In the dark, they are able to grow due to the oxidation of organic substances. The cell wall of dinoflagellates is made up of cellulose. These planktonic unicellular algae have two lateral flagella. Microscopic representatives of green algae live in fresh and marine water bodies, in the soil and on the surface of various terrestrial objects. They can be motionless or move with the help of flagella. Green microalgae have a cellulose cell wall and store starch in their cells. They are able to reproduce both asexually and sexually.

Mushrooms are divided into groups according to the characteristics of their reproduction. Imperfect fungi include representatives in which no sexual reproduction. Traditional microbiological objects - types of genera Penicillium, Aspergillus, Candida, Rhodotorula and others are included in this group. The group of zygomycetes is made up of fungi that have coenocytic mycelium and form a zygospore by the fusion of two parental hyphae during the sexual process. Known genera of Zygomycetes are Mucor and Rhizopus. Mushrooms that form a special bag (ask) for sporulation are called ascomycetes. They have a septate mycelium, and during asexual reproduction they form conidia (chains of spores collected in brushes or heads). This group includes genera Neurospora, Saccharomyces, Lipomyces, Cryptococcus. Some yeasts and most of the higher hat fungi are basidiomycetes. During sexual reproduction, they form a special swollen hypha (basidia), which forms outgrowths with spores. The mycelium of basidiomycetes is divided by partitions.

important place in economic activity a person is occupied by representatives of the combined non-taxonomic group of yeasts. It includes mushrooms, which are characterized by the absence or a significant reduction in the mycelial stage of growth. Best known as yeast representatives of the genera Saccharomyces, Lipomyces, Candida, Rhodotorula, Pichia. The morphology and metabolism of yeasts largely depends on the growing conditions. Many yeasts exist for a long time as separate immobile cells and reproduce by budding. Most yeasts are facultative anaerobes. There are also pathogenic species among yeasts (for example, candida albicans is the causative agent of "thrush").

Main groups of prokaryotic microorganisms

Prokaryotic microorganisms are grouped into two separate domains: Bacteria and Archaea. The division of these groups occurred based on the results of comparison of 16S rRNA nucleotide sequences, as well as due to significant differences in the composition of cell walls, lipids, and due to metabolic features. Archaea differ from bacteria and eukaria in a number of essential ways. In ordinary lipids, glycerol is linked by an ester bond to fatty acids, and in archaea, by an ether bond to the isoprenoid C 20 alcohol, phytanol. . Phytanol chains may contain five-membered rings. Archaeal lipids are able to form tetramers (C40), so the membrane composed of tetramers is more rigid than a traditional bilayer due to the lack of internal space. Archaea can have both conventional bilayer and rigid monolayer membranes. The more extreme the conditions of their habitat, the more monolayer regions are contained in their CPM.

In archaea, peptidoglycan (murein) cell walls typical of bacteria have not been found. The composition of the cell walls of archaea may include another heteropolysaccharide - pseudomurein, which lacks N-acetylmuramic acid. Some archaea may have a protein S-layer on top of the CPM as a cell wall. Another way to organize archaea is complete absence cell wall, when the membrane is almost entirely represented by a rigid monolayer of tetramers, reinforced big amount five-membered rings, for example, as in Thermoplasma.

In a number of ways, archaea are closer to eukaria than to bacteria. So, like eukaryotes, archaea have intron regions in DNA, as well as histone-like proteins associated with nucleic acids. Halophilic archaea are able to carry out chlorophyll-free photosynthesis associated with the functioning of a special protein, bacteriorhodopsin, which is similar in many properties to rhodopsin in the retina of animals. Many archaea live in extreme environments and grow sparsely. However, in such habitats they have few competitors, which has allowed them to survive to the present day.

Archaea domain divided into three phyla: Euryarchaeota, Crenarchaeota and Korarchaeota. The first includes ubiquitous microorganisms of several physiological and systematic groups. These are methanogens - strict anaerobes that live in the bottom sediments of freshwater zones rich in organic matter, or in the rumen of ruminants. Extreme halophiles (haloarchaea) are also widespread, growing at high salt concentrations and capable of performing a special type of photosynthesis with the help of bacteriorhodopsin, which works like a proton pump in the light. Thermoplasmas living in hot acidic springs and obligately anaerobic thermococci develop at high temperatures, and thermoplasmas are devoid of cell walls. This phylum also includes extremely thermophilic sulfate reducers.

The second phylum includes microorganisms that live in very specific places with narrow boundaries for the values ​​of physicochemical factors. These are extremophiles dependent on sulfur compounds, whose optimum pH and growth temperatures are characterized by extreme values.

The third phylum is reserved for groups whose representatives are not amenable, but for which the sequences of genes encoding the 16S rRNA molecule are known.

Domain Bacteria combines prokaryotic microorganisms that have typical features of bacteria, in particular, cell membranes containing peptidoglycan. Currently, the domain is divided into 23 phyla, which contain cultivated representatives, all or part of which are obtained as pure cultures.

The systematics (taxonomy) of organisms consists in the distribution (classification) of them into certain groups, each of which has its own name: class, order, family, genus, species. A species is the basic taxonomic unit. The classification of all living beings is based almost entirely on morphological features organisms. In bacteria, the classification has specific features due to the small number of their morphological characters. Modern microbiology uses a set of features for classification: morphological (cell shape, presence and location of flagella, method of reproduction, Gram stain, ability to form endospores ; physiological features (way of nutrition, energy production, composition of metabolic products, attitude to the effects of temperature, pH, oxygen, and other factors ); cultural (the nature of growth on various nutrient media of bacterial culture; on liquid media> - the presence of a film, turbidity, sediment; on dense media - the type of colonies and their features). Most classifications of bacteria are artificial. They are designed to identify a particular group of microorganisms of interest to researchers. Unlike artificial, natural reflects the gradual development (evolution) of living organisms.

IN last years the artificial classification of bacteria proposed by R. Murray in 1978 was recognized. It is based on the structure of the cell wall. IN first department all bacteria are classified, which are characterized by the structure of the cell wall according to the type Gram+ bacteria: all cocci, lactic acid bacteria (pediococci - Pediococcus, lactobacilli - Lactobacillus, streptococci - Streptococcus and leuconostoc - Leuconostoc), rod-shaped spore-forming bacteria (Bacillus, Clostridium) and actinomycetes. Second department 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-sticks 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 the causative agents of infectious gastrointestinal diseases (dysentery, typhoid, paratyphoid), transmitted through food, and food poisoning. Third department combines special forms of bacteria that lack a true cell wall, they do not play a role in food production, and therefore will not be considered.

In accordance with the rules accepted in biology, proposed back in the 18th century. K. Linnaeus, the name of microorganisms is given in Latin and consists of two words. The first designates the genus and is written with a capital letter, the second - the species to which the organism belongs - is written with a lowercase letter. For example: "Bacillus subtilis (hay stick) is a bacterium belonging to the genus Bacillus, rod-shaped, forming bacillary-type endospores, lives in hay.

Eukaryotes (filamentous fungi and yeasts)

Fungi make up a large group of organisms that are separated into a separate kingdom, Mycota. Mushrooms have a mycelial structure. The methods of reproduction of fungi are diverse (vegetative, asexual and sexual) and specific.

Mushrooms are divided into macromycetes And micromycetes (filamentous fungi and yeast). The former form large fruit bodies, the latter lack them, and their entire life cycle is represented by microscopic structures.

Mushrooms are one of the largest and most diverse groups of organisms and include about 80 thousand species.

Mushrooms are widely distributed in nature and occupy a wide variety of habitats, both in water and on land. In practice, their spores can be found on any natural substrates, artificial materials and products. Among the fungi there are organisms that develop on dead organic residues; there are also those that can exist only in living organisms and cause their diseases. Some fungi secrete toxic substances - mycotoxins.

Fungi can spoil many foods, potato grains, and wood and other materials, including glass. But mushrooms are also of great practical importance, many of them are eaten, used in the production of ethyl alcohol, organic acids, enzymes, antibiotics, vitamins, etc.

Lecture No. 5 Morphology and systematics of microorganisms. Prokaryotes (bacteria and actinomycetes).

1 Morphology and systematics of microorganisms. Morphology of microorganisms studies them appearance, shape and structural features, the ability to move, spore formation, methods of reproduction. Morphological features play an important role in the recognition and classification of microorganisms. Since ancient times, the living world has been divided into two kingdoms: the kingdom of plants and the kingdom of animals. When the world of microorganisms was discovered, they were separated into a separate kingdom. Thus, until the 19th century, the whole world of living organisms was divided into three kingdoms. At the beginning, the classification of microorganisms was based on morphological characteristics, since a person knew nothing more about them. By the end of the 19th century, many species had been described; different scientists, mainly botanists, divided microorganisms into groups accepted for the classification of plants. In 1897, for the systematics of microbes, they began to use, along with morphological, and physiological signs. As it turned out later, for a scientifically based classification, some signs alone are not enough. Therefore, a set of features is used:

Morphological (cell shape, size, mobility, reproduction, sporulation, Gram stain);

Cultural (character of growth on liquid and solid nutrient media);

Physiological and biochemical (nature of accumulated products);

Genotypic (physical and chemical properties of DNA).

Genosystematics allows you to determine the type of microorganisms not by similarity, but by kinship. It has been established that the nucleotide composition of total DNA does not change during the development of microorganisms under different conditions. S- and R-forms are identical in DNA composition. Microorganisms have also been found that have a similar nucleotide composition of DNA, although they belong to different systematic groups: Escherichia coli and some corynebacteria. This indicates that the systematics (taxonomy) of microbes should take into account different features.

Until recently, all living beings cellular structure depending on the relationship of the nucleus and organelles with the cytoplasm, the composition of the cell wall and other features, they were divided into two groups (kingdoms):

1.1 Prokaryotes-prenuclear (classified - organisms that do not have a clearly defined nucleus, represented by a DNA molecule in the form of a ring; peptidoglycan (murein) and teichoic acids are part of the cell wall; ribosomes have sedimentation constants of 70; energy centers of the cell are located in mesosomes and there are no organelles ).

1.2 Nuclear eukaryotes (with a clearly defined nucleus separated from the cytoplasm by a membrane; peptidoglycan and teichoic acids are absent in the cell wall; cytoplasmic ribosomes are larger; sedimentation constant is 80; energy processes are carried out in mitochondria; there is a Golgi complex from organelles, etc.).

Later it turned out that among microorganisms there are also non-cellular forms-viruses, and therefore a third group (kingdom) was identified - vira.

To designate microorganisms, a double (binary) nomenclature is adopted, which includes the name of the genus and species. The generic name is written with a capital letter (capital), the species name (even derived from a surname) is written with a lowercase (small). For example, anthrax bacillus is called Bacillus anthracis, Escherichia coli is called Escherichia coli, black aspergillus is called Aspergillus niger.

The basic (lower) taxonomic unit is the species. Species are grouped into genera, genera into families, families into orders, orders into classes, classes into divisions, and divisions into kingdoms.

A species is a collection of individuals of the same genotype with a pronounced phenotypic similarity.

Culture - microorganisms obtained from an animal, human, plant or environmental substrate and grown on a nutrient medium. Pure cultures consist of individuals of the same species (the offspring obtained from one cell is a clone).

A strain is a culture of the same species isolated from various environments habitats and characterized by minor changes in properties. For example, E. coli isolated from the human body, cattle, water bodies, soil, can be of different strains.

2 Prokaryotes (bacteria and actinomycetes). Bacteria (prokaryotes) are a large group of microorganisms (about 1600 species), most of which are unicellular. Shape and size of bacteria. The main forms of bacteria are spherical, rod-shaped and convoluted. Spherical bacteria - cocci have the usual shape of a ball, there are flattened, oval or bean-shaped. Cocci can be in the form of single cells - monococci (micrococci) or connected in various combinations: in pairs - diplococci, four cells - tetracocci, in the form of more or less long chains - streptococci, and also in the form of clusters of a cubic shape (in the form of packages) of eight cells arranged in two tiers, one above the other, are sarcins. Clusters meet irregular shape resembling bunches of grapes - staphylococci. Rod-shaped bacteria can be single or connected in pairs - diplobacteria, chains of three to four or more cells - streptobacteria. The ratios between the length and thickness of the sticks are very different. Curved, or curved, bacteria vary in length, thickness, and degree of curvature. Sticks slightly curved in the form of a comma are called vibrios, sticks with one or more corkscrew curls are called spirilla, and thin sticks with numerous curls are called spirochetes. Thanks to the use of an electron microscope to study microorganisms in natural substrates, bacteria were found that have a special shape of cells: a closed or open ring (toroids); with outgrowths (prostekami); worm-shaped - long with curved very thin ends; and also in the form of a hexagonal star.

Bacteria are very small, ranging from tenths of a micrometer (µm) to a few micrometers. On average, the body size of most bacteria is 0.5-1 microns, and the average length of rod-shaped bacteria is 2-5 microns. There are bacteria that are much larger than average value, and some are on the verge of visibility in conventional optical microscopes. The body shape of bacteria, as well as their size, can vary depending on age and growth conditions. However, under certain, relatively stable conditions, bacteria retain their inherent this species sizes and shape. Weight bacterial cell very small, approximately 4-10-1:! G.

The structure of a bacterial cell . The cell of prokaryotic organisms, which include bacteria, has the fundamental features of the ultrastructure. The cell wall (shell) is an important structural element of most bacteria. The cell wall accounts for 5 to 20% of the dry matter of the cell. It has elasticity, serves as a mechanical barrier between the protoplast and the environment, gives the cell a certain shape. The cell wall contains a heteropolymer compound specific for prokaryotic cells - peptidoglycan (murein), which is absent in the cell walls of eukaryotic organisms. According to the staining method proposed by the Danish physicist H. Gram (1884), bacteria are divided into two groups: gram-positive and gram-negative. Gram-positive cells retain the dye, while Gram-negative cells do not, due to differences in the chemical composition and ultrastructure of their cell walls. Gram-positive bacteria have thicker, amorphous cell walls, they contain a large amount of murein (from 50 to 90% of the dry mass of the cell wall) and teichoic acids. The cell walls of gram-negative bacteria are thinner, layered, they contain a lot of lipids, little murein (5-10%) and no teichoic acids.

The cell wall of bacteria is often covered with mucus. The mucous layer may be thin, barely visible, but may be significant, may form a capsule. Often the capsule is much larger than the bacterial cell. The mucus of the cell walls is sometimes so strong that the capsules of individual cells merge into mucous masses (zoogels) in which bacterial cells are interspersed. Mucous substances formed by some bacteria are not held in a compact mass around the cell wall, but diffuse into the environment. When rapidly multiplying in liquid substrates, mucus-forming bacteria can turn them into a continuous slimy mass. This phenomenon is sometimes observed in sugary extracts from beets in the production of sugar. In a short time, sugar syrup can turn into a viscous slimy mass. Meat, sausages, cottage cheese are subjected to mucus; the viscosity of milk, brines, pickled vegetables, beer, wine is observed. The intensity of mucus formation and the chemical composition of mucus depend on the type of bacteria and cultivation conditions. The capsule has useful properties, mucus protects cells from adverse conditions - in many bacteria, mucus formation increases under such conditions. The capsule protects the cell from mechanical damage and drying out, creates an additional osmotic barrier, serves as an obstacle to the penetration of phages, antibodies, and sometimes it is a source of reserve nutrients. The cytoplasmic membrane separates the contents of the cell from the cell wall. This is a mandatory structure of any cell. If the integrity of the cytoplasmic membrane is violated, the cell loses its viability. The cytoplasmic membrane accounts for 8-15% of the dry matter of the cell. The membrane contains up to 70-90% of cell lipids, its thickness is 7-10 nm 1 . On sections of cells in electron microscope it is visible in the form of a three-layer structure - one lipid layer and two protein layers adjacent to it on both sides. The cytoplasmic membrane in places protrudes into the cell, forming all kinds of membrane structures. It contains various enzymes; she is semi-permeable, plays important role in the exchange of substances between the cell and the environment. The cytoplasm of a bacterial cell is a semi-fluid, viscous, colloidal system. In some places, it is permeated with membrane structures - mesosomes, which originated from the cytoplasmic membrane and retained their connection with it. Mesosomes perform various functions; in them and in the cytoplasmic membrane associated with them there are enzymes involved in energy processes - in supplying the cell with energy. Well-developed mesosomes are found only in gram-positive bacteria; in gram-negative bacteria, they are poorly developed and have a simpler structure. The cytoplasm contains ribosomes, a nuclear apparatus and various inclusions. Ribosomes are scattered in the cytoplasm in the form of 20–30 nm granules; Ribosomes are about 60% ribonucleic acid (RNA) and 40% protein. Ribosomes are responsible for cell protein synthesis. In a bacterial cell, depending on its age and living conditions, there may or may not be 5-50 thousand ribosomes. The nuclear apparatus of bacteria is called the nucleoid. electron microscopy Ultrathin sections of bacterial cells made it possible to establish that the carrier of the cell's genetic information is the deoxyribonucleic acid (DNA) molecule. DNA has the form of a double helical strand closed in a ring; it is also called the "bacterial chromosome". It is located in a certain area of ​​the cytoplasm, but is not separated from it by its own membrane.

Cytoplasmic inclusion bacterial cells are diverse, mainly these are reserve nutrients that are deposited in cells when they develop in conditions of excess nutrients in the environment, and are consumed when cells fall into starvation conditions. Polysaccharides are deposited in bacterial cells: glycogen, a starch-like granulose substance, which are used as a source of carbon and energy. Lipids are found in cells in the form of granules and droplets. Fat serves good source carbon and energy. Many bacteria accumulate polyphosphates; they are contained in volutin granules and are used by cells as a source of phosphorus and energy. Molecular sulfur is deposited in the cells of sulfur bacteria.

Mobility of bacteria . Globular bacteria are usually immobile. Rod-shaped bacteria are both mobile and non-motile. Curved and spiral bacteria are mobile. Some bacteria move by sliding. The movement of most bacteria is carried out using flagella. Flagella are thin, spirally twisted filaments of a protein nature that can carry out rotational movements. The length of the flagella is different, and the thickness is so small (10-20 nm) that they can be seen in a light microscope only after special processing of the cell. The presence, number, and arrangement of flagella are constant features for the species and have diagnostic value. Bacteria with one flagellum at the end of the cell are called monotrichous; with a bunch of flagella - lofotrichs ", with a bunch of flagella at both ends of the cell - amphitriches; bacteria in which flagella are located on the entire surface of the cell are called peritrichous. The speed of movement of bacteria is high: in a second a cell with flagella can travel a distance of 20-50 times more than the length of its body.Under unfavorable living conditions, with aging of the cell, with mechanical action, mobility may be lost.In addition to the flagella, on the surface of some bacteria there are a large number of filamentous formations, much thinner and shorter than the flagella - fimbriae (or pili) .

Reproduction of bacteria. Prokaryotic cells are characterized by simple cell division in two. Cell division begins, as a rule, some time after the division of the nucleoid. Rod-shaped bacteria divide across, spherical shapes in different planes. Depending on the orientation of the fission plane and their number, various forms arise: single cocci, paired, chains, in the form of packages, clusters. A feature of the reproduction of bacteria is the speed of the process. The rate of division depends on the type of bacteria, cultivation conditions: some species divide every 15-20 minutes, others - after 5-10 hours. With this division, the number of bacterial cells per day reaches huge amount. This is often observed in food products: rapid souring of milk due to the development of lactic acid bacteria, rapid spoilage of meat and fish due to the development of putrefactive bacteria, etc.

Sporulation. Spores in bacteria are usually formed under unfavorable conditions of development: with a lack of nutrients, changes in temperature, pH, with the accumulation of metabolic products above a certain level. Rod-shaped bacteria have the ability to form spores. Each cell produces only one spore (endospore).

Sporulation is a complex process, several stages are distinguished in it: first, a restructuring of the genetic apparatus of the cell is observed, and the morphology of the nucleoid changes. DNA synthesis stops in the cell. The nuclear DNA is pulled out as a strand, which is then split; part of it is concentrated at one of the poles of the cell. This part of the cell is called the sporogenous zone. In the sporogenous zone, the cytoplasm becomes denser, then this area is separated from the rest of the cellular contents by a septum (septa). The cut-off area is covered by the membrane of the mother cell, the so-called prospore is formed. A prospore is a structure located inside the mother cell, from which it is separated by two membranes: outer and inner. A cortical layer (cortex) is formed between the membranes, similar in chemical composition to the cell wall of a vegetative cell. In addition to peptidoglycan, the cortex contains dipicolinic acid (C 7 H 8 O 4 Mg), which is absent in vegetative cells. Subsequently, a spore shell is formed on top of the prospore, consisting of several layers. The number, thickness and structure of the layers are different in different types of bacteria. The surface of the outer shell can be smooth or with outgrowths. different lengths and forms. On top of the spore shell, a thin cover is often formed that surrounds the spore in the form of a sheath, the exosporium.

Spores are usually round or oval in shape. The diameter of the spores of some bacteria exceeds the width of the cell, as a result of which the shape of the spore-bearing cells changes. The cell takes the form of a spindle (clostridium) , if the spore is located in its center, or the shape of a drumstick (plectridium) when the spore is near the end of the cell.

After maturation of the spore, the mother cell dies, its shell is destroyed, and the spore is released. The spore formation process takes several hours.

The presence of a dense, impermeable membrane in bacterial spores, a low water content in it, a large amount of lipids, as well as the presence calcium And dipicolinic acid determine the high resistance of spores to environmental factors. Spores can survive for hundreds or even thousands of years. For example, viable spores have been isolated from the corpses of mammoths and Egyptian mummies, which are thousands of years old. Spores are resistant to high temperature: in a dry state, they die after heating at 165-170 ° C for 1.5-2 hours, and with superheated steam (in an autoclave) - at 121 ° C for 15-30 minutes.

Under favorable conditions, the spore germinates into a vegetative cell; this process usually takes several hours.

The germinating spore begins to actively absorb water, its enzymes are activated, and biochemical processes leading to growth are intensified. During spore germination, the cortex turns into the cell wall of a young vegetative cell; dipicolinic acid and calcium are released into the external environment. The outer shell of the spore is torn, through the gaps the "sprout" of a new cell comes out, from which a vegetative bacterial cell is then formed.

Food spoilage is caused only by vegetative cells. Knowledge of the factors that contribute to the formation of spores in bacteria, and the factors that cause them to grow into vegetative cells, is important in choosing a method for processing products in order to prevent their microbial spoilage.

The above information characterizes mainly the so-called true bacteria. There are others, more or less different from them, which include the following.

Filamentous (filamentous bacteria). These are multicellular organisms in the form of threads of various lengths, with a diameter of 1 to 7 microns, mobile or attached to the substrate. Mostly filaments with a slimy sheath. They may contain magnesium oxide or iron oxides. They live in water bodies, are found in the soil.

Myxobacteria. These are rod-shaped bacteria that move by sliding. They form fruiting bodies - clusters of cells enclosed in mucus. Cells in fruit bodies go into a dormant state - myxospores. These bacteria live in the soil, on various plant debris.

Budding and stalk bacteria reproduce by budding, forming stalks, or both. There are species with outgrowths - prostheca. They live in soil and water bodies.

Actinomycetes. Bacteria are branched. Some are slightly branched sticks (see Fig. 2, e), others are in the form of thin branching filaments that form a unicellular mycelium. Mycelial actinomycetes, called "radiant fungi", reproduce by spores that develop on the aerial branches of the mycelium. Actinomycetes are colored; they are widely distributed in nature. They are also found on food products and can cause spoilage. The product acquires a characteristic earthy odour. Many actinomycetes produce antibiotics. There are species that are pathogenic to humans and animals.

Mycoplasmas. Organisms without a cell wall are covered only by a three-layer membrane. The cells are very small, sometimes ultramicroscopic in size (about 200 nm), pleomorphic (of various shapes) - from coccoid to filamentous. Some cause diseases in humans, animals, plants.

Fundamentals of taxonomy of bacteria Modern bacterial classification systems are essentially artificial, combining bacteria into certain groups based on their similarity in terms of a complex of morphological, physiological, biochemical and genotypic characters. For this purpose, Bergi's guide to the definition of bacteria (1974, 8th edition and 1984) is used. - 9th edition). According to the 8th edition, all prokaryotes are divided into two divisions - cyanobacteria and bacteria. The first section - cyanobacteria (blue-green algae) - are phototrophic microorganisms. The second section is bacteria. This department is divided into 19 groups. The 17th group includes actinomycetes. According to the 9th edition, the prokaryotic kingdom is subdivided into four divisions depending on the presence or absence of a cell wall and its chemical composition: in the first section - thin-skinned, groups of bacteria, gram-negative, phototrophic and cyanobacteria are included; in the 2nd department - hard-skinned, groups of bacteria are included that are positive for Gram stain; the third section includes mycoplasmas - bacteria that do not have a cell wall; the fourth section includes methane-forming and archaebacteria (a special group of bacteria that lives in extreme environmental conditions and is one of ancient forms life).


Biological systematics is a major branch of biology, the main tasks of which include the definition of all living organisms studied by science into a single system. The taxonomy of bacteria began to develop actively only at the end of the 20th century. It was then that methods were found, thanks to which scientists were able to identify the basic principles of the life of numerous representatives of the bacterial kingdom.

Modern system

In view of the fact that man has just begun the study of microorganisms, a complete scheme of the prokaryotic community in microbiology does not yet exist. In general, it is difficult to say with certainty that someday it will be compiled. If we recall one of the main postulates that guides the entire scientific world, that the knowledge of nature is inexhaustible, then it is difficult to imagine that someday mankind will hear from representatives of microbiology a statement about the completion of the taxonomy of bacteria.

A clear example of the influence of new discoveries on taxonomy is the relatively recent division of the once unified kingdom of bacteria and the separation from it of the kingdom of archaea. Having the opportunity to study in detail the structure of both organisms, scientists came to the conclusion that archaea are more like eukaryotic cells in their structure, although they are nuclear-free prokaryotes. It is now believed that it was the archaea that became the transitional link between protozoa and eukaryotes.

But, despite the relatively short period of existence of microbiology, the systematization of bacteria is based on all those basic principles that allow us to combine all living things into a coherent scheme. These principles were formulated at the end of the 18th century by the Swedish scientist Carl Linnaeus, who was the first to set out to create a unified system of living nature.

These principles are the following axioms:

  1. The structure of living diversity is based on a single common structure.
  2. The overall structure is built on a hierarchical principle.
  3. The result of the knowledge of the general structure can be a single system of living nature.

As for the main practical tasks that systematics solves in microbiology, these are:

  • classification - ranking of known living organisms according to biological taxa (taxon - classification unit);
  • identification - work with unknown living organisms to establish their belonging to one or another existing taxa;
  • nomenclature - the way in which names are assigned to living organisms.

Classification and identification

With the accumulation of knowledge about bacterial organisms, scientists were able to determine the similarities and differences between individual representatives of this kingdom. It is the identification of similar features that is the basis for the classification of bacteria by taxa.

However, here everything is not as simple as it seems. For example, if you take two round unicellular cocci (round bacteria), you can easily determine their similarity in shape. But this is not enough to competently declare that these cocci belong to the same taxon. For such statements, it is necessary to establish in the available cocci the general ones:

  • phenotypic properties (body structure),
  • genotypic properties (the structure of the body's genes).

By studying the data collected on the structural features of microorganisms, it is possible to identify characteristics that will further determine the place of the bacterium in the general classification:

  • morphology - sizes, shapes and their relationships;
  • Gram stain (gram-negative or gram-positive);
  • biochemical - what substances are formed during the bacterial life cycle;
  • the presence in the body of the ability to produce antibodies (antigenic);
  • physiology (nutrition, respiration, reproduction);
  • the ability to form disputes;
  • degree of homogeneity of genes.

The study of each individual feature of the structure and vital activity of a bacterium provides a lot of information about its belonging to one or another taxa. So, for example, there are only a few ways of reproduction of bacteria, and this despite the fact that reproduction always occurs by division.

Bacteria are widely distributed in nature, their characteristic feature is cosmopolitanism. The available data on the geographical distribution and specificity of bacteria do not yet make it possible to use them for systematic purposes.[ ...]

Systematics of spore-forming anaerobic bacteria.[ ...]

The taxonomy of spore-forming bacteria has evolved along with the evolution of views on the principles of differentiation and identification of microbial species, as well as the improvement of methods for the morphological and physiological study of bacteria.[ ...]

Systematics of bacteria is carried out on the basis of certain characteristics in a group of microorganisms. To isolate bacteria at a specific systematic group a thorough study of morphology, ability to move, spore formation is necessary. A distinctive feature is the ratio of cells to staining. The most commonly used method for differentiating microorganism cells is Gram staining. The essence of this method is to find out the possibility of holding the dye (crystal violet - iodine) by the cell during subsequent treatment of the drug with alcohol. The use of this indicator method allows us to distinguish two groups of microorganisms: gram-positive, retaining color; and gram-negative, discolored when the preparation is treated with alcohol.[ ...]

Questions of taxonomy of bacteria are of exceptional importance for research and study of the formation of various physiologically active substances of microbial origin. A biological species represents the unity of specific morphological and physiological-biochemical characteristics of an organism that determine all the features of its vital activity, distribution and interaction with the external environment. In this regard, the formation of one or another product of vital activity, as well as characteristic biological features, cannot be imagined in isolation from the species of the microorganism.[ ...]

For the isolation of bacteria into independent species, some authors consider the enzymatic properties of organisms to be decisive, others - morphological and cultural characteristics, others - the cytological features of the bacterial cell, etc. In all such cases, the principles of taxonomy change as new features in the structure and physiological properties of organisms are revealed. and using them as signs of species identification. The taxonomy of different types of spore-forming bacteria reflects the degree of their study, and therefore, should develop and change as new data are accumulated.[ ...]

Phylogenetic systematics is developed at all taxonomic levels, from species and subspecies to the level of higher taxonomic units - classes, divisions (types) and kingdoms. In this final part of the chapter, we will focus on the macrosystem of living beings, that is, on their highest taxonomic units- kingdoms and sub-kingdoms. This question is extremely important for all biology in general and especially for botany in connection with the question of the systematic position of bacteria, blue-green algae and fungi.[ ...]

The peculiarities of the structure of bacteria do not allow in their study to apply all those methods that are successfully used in botany. The simplicity of the structure of bacteria, the absence of a typical nucleus and other organelles in their cells, as well as the sexual process, exclude the possibility of using the cytomorphological method to the extent that it takes place in plant systematics. The historical method is also excluded here. We know almost nothing about the distant past of bacteria. The available indications of the fossilized remains of bacteria are few and do little to explain the historical processes of the evolutionary development of these organisms.[ ...]

Artificial classifications of bacteria are simpler and their tasks are less complicated. They were created with the aim of speeding up the cataloging of microbes and speeding up the recognition or identification of beneficial or harmful organisms of practical importance. An artificial, or nomenclature, classification is also the basis for the taxonomy of bacteria used in most bacterial determinants, including those published in the USSR: L. M. Horowitz-Vlasova, V. D. Shtiben and I. K. Babich, Zion and Bergi. Of these, only determinants can be recommended for determining bacteria isolated from sewage treatment plants, settling tanks, lagoons, reservoirs, collections of industrial effluents, purification ponds, maps on irrigation fields and various reservoirs contaminated with wastewater: Bergi - Russian translation of the 4th edition; N. A. Krasilnikova and Berga's 7-8th editions.[ ...]

Ivanov V. I., Lya likov a N. N. On the taxonomy of iron-oxidizing thionic bacteria. "Microbiology", vol. XXXI, no. 3, 1962.[ ...]

A possible and desirable biochemical method of systematics, unfortunately, as applied to microbiology, remains poorly developed. However, some biochemical works are of considerable interest, as they provide grounds for dividing bacteria into groups and species.[ ...]

In the presentation of questions concerning the taxonomy and systematics of prokaryotes, we adhere to the interpretation adopted in the 8th edition of Berga's Key to Bacteria. This order includes organisms that form either a true mycelium or branching filaments and have other common features. These bacteria do not form mycelium, they look like irregularly shaped rods - curved or clavate-swollen, sometimes coccoid. Most actinomycete-related bacteria show a tendency to polymorphism and the formation of cells with little branching.[ ...]

However, the serological method is not used for taxonomy of bacteria to the extent that one would expect. In most cases, it fails to identify or separate species. Numerous attempts in this direction give conflicting results, clearly inconsistent with the indicators obtained by other methods. The serological method is most well developed for the differentiation of bacteria of the intestinal group.[ ...]

Gram-positive esporogenic rod-shaped bacteria, which include lactic acid bacteria - fam. Systematics, ecology and biology of lactic acid bacteria in the Soviet Union was developed in detail by E. I. Kvasnikov and O. A. Nesterenko.[ ...]

new organisms. As has been repeatedly noted, the competition of the taxonomy of microorganisms with ever new mysteries of nature continues uninterruptedly. An object recently presented for identification - a gram-negative non-spore-forming bacterium with a hexagonal cell (Fig. 36) - cannot be assigned to any of the existing taxa (classification groups) and is assigned to itself, remaining the only representative of this group. This group got a random name - Stella (star).[ ...]

Spore-forming bacteria can use both simple sugars and polysaccharides as a source of carbon nutrition. Of the monosaccharides, they best absorb glucose, and of the disaccharides, sucrose. The ratio of different types of spore-forming bacteria to carbohydrates is different, which is widely used in taxonomy studies to determine the species of microorganisms.[ ...]

From the foregoing, we can conclude that the numerical, or Adansonian, taxonomy did not introduce anything new into the taxonomy of bacteria, which would make it possible to put its merits above traditional taxonomy. And if we compare numerical systematics with genetic systematics based on the study of the nucleotide composition, then we have to admit that the biochemical study of the nucleotide composition forms a new foundation for the systematics of bacteria, which cannot be said about the numerical (digital) systematics. However, at present, "...neither iumeric methods, nor chemical determinations of the genetic proximity of organisms can be used as the basis for building a system" (G. A. Zavarzin, ).[ ...]

The functional kingdoms of communities may not be identical to the kingdoms in taxonomy, but they largely form their evolutionary basis. In the traditional system of the Two Kingdoms, the animal kingdom included both unicellular and multicellular organisms, characterized by the ability to swallow food and mobility, while the vast plant kingdom included mainly photosynthetic groups and (somewhat arbitrarily co-operated with them) bacteria and fungi. In the modern alternate division of life forms, bacteria (together with blue-green algae) form the Mopega kingdom, being prokaryotes, while higher plants and animals also constitute kingdoms characterized by the direction of evolution discussed above. At the same time, it is quite logical to consider higher mushrooms separate kingdom, and unite eukaryotic unicellular organisms into the kingdom Protista.[ ...]

The reader can easily conclude from the example of the presented material that the problems of taxonomy of bacteria are among the most complex. Being heterotrophs, they have unique physiology features (economical metabolism). Undoubtedly, they occupy a special position among non-spore-forming bacteria.[ ...]

Razumov AS Microbial indicators of saprobity of reservoirs polluted by industrial waters. 111.[ ...]

Among prokaryotes, blue-green algae turned out to be in the most advantageous position. Their study and the construction of systematics were developed by algologists, and not by microbiologists. In algology, as in other branches of botany, taxonomy was based on phylogenetic principles. This, undoubtedly, was favored by a significantly larger number of morphological characters and a greater diversity biological features, in particular, reproduction and the formation of resting (surviving) forms than bacteria. IN best position than other bacteria, there are also higher forms of actinomycetes, which have mycelium and specialized sporulation organs. Morphological characters for the construction of phylogenetic systematics are undoubtedly more reliable than some physiological and many biochemical ones.[ ...]

The most natural natural taxon is the species - the classification unit of the lowest rank. Modern systematics includes five higher taxa in wildlife, the representatives of which differ in the type of metabolic processes and role in nature: these are bacteria, protozoa, fungi, plants and animals. In each of these large groups of organisms one can find more primitive and more morphologically and physiologically complex representatives, all of them in high degree adapted to their environment.[ ...]

However, the assessment of the biodiversity of the biocenosis as a whole in terms of the number of species will be incorrect if we do not take into account the size of the organisms. After all, the biocenosis includes both bacteria and macroorganisms. Therefore, it is necessary to combine organisms into groups that are similar in size. Consortia - a group of heterogeneous organisms that settle on the body or in the body of an individual of a certain species - the central member of the consortium, capable of creating a certain microenvironment around itself. Other members of the consortium can create smaller consortia, etc., i.e., consortia of the first, second, third, etc. order can be distinguished. From this it is clear that biocenosis is a system of interconnected consortia.[ ...]

Only those species that are of practical importance (pathogenic, fermentative forms, producers of various antibiotics, enzymes, etc.) have been well studied. The issues of taxonomy of spore-forming bacteria were studied by specialists in applied sciences for diagnostic purposes, mainly for sanitary and hygienic purposes.[ ...]

This grouping of legumes with their respective Rhizobium species was especially useful for the production of inoculums. After initially splitting into cross-inoculating groups, taxonomists and inoculum manufacturers have turned their attention to other traits and techniques by which Rhizobium species can be characterized in more detail: growth rate, induced antibiotic activity, immunofluorescence, and longevity.[ ...]

Types of microorganisms are subdivided according to the totality of morphological, physiological and biochemical characteristics. Each organism has many characters, but not every character can be used in taxonomy. There are leading signs that characterize the species, and subordinate signs. The leading feature may be different indicators for different groups of bacteria. For some species, this is the ability to assimilate carbohydrates, for others - to form antibiotics, for others - to ferment sugar or synthesize specific metabolites, pigments, acids, hormones, etc. In some species, the leading feature is the ability to form nodules on the roots or leaves of plants . Some species are classified according to their enzymatic properties, such as acetic acid, lactic acid, propionic acid and other bacteria. Many species are classified according to their virulence and pathogenicity in relation to plants, animals and humans.[ ...]

Blue-green algae or cyanophycea (their structure is described in detail on pages 39-43). Previously, these organisms were considered only in manuals on algology, now some researchers attribute them to bacteria. Their taxonomy, as we have already indicated above, is better developed than the actual bacteria (zubacteria), and is detailed in the literature. It is based solely on morphological features.[ ...]

The problem of microbial variability has been a subject of discussion since the emergence of microbiology as a science. From the 70s of the XIX century. to this day, variability is one of the brightest and most fascinating chapters of microbiology. The study of the variability of bacteria has brought a lot of valuable material to create a picture of the ontogenetic development of many species. Experimental variability, in the opinion of leading experts in bacterial taxonomy, can serve as one of the most fruitful methods for elucidating the place of an organism in a system when trying to establish phylogenetic relationships. Laboratory variability in the experiment helps to determine the boundaries of the species and genus of bacteria.[ ...]

The scope of this book does not allow us to list all the groups of pathogens that we may encounter in rooms, conservatories and botanical garden collections. Only the most common and most dangerous pathogens are described here. More in-depth and detailed information on the systematics, biology and control of other pathogens not included in the book can be found in the special scientific and reference literature on individual groups phytopathogenic fungi, bacteria, viruses.[ ...]

Some types of microbes form various pigments: red, blue, green, orange, brown, black and mixed colors. Most microbes do not form pigments, their colonies are colorless. Pigments are a stable sign that is inherent in certain types of microbes. This feature can also be used in the taxonomy of bacteria. The biological significance of pigments is still little known.[ ...]

One of the characteristic features of antibiotics is the selectivity of action - each antibiotic acts on a certain set of types of microorganisms, that is, it has its own specific antimicrobial spectrum of action. For example, actinomycetes belonging to the species Actinomyces streptomycini inhibit the growth of gram-positive and gram-negative bacteria, mycobacteria, some types of yeast and fungi. Antibiotics produced by actinomycetes do not inhibit the development of their own culture, even at concentrations that are many times higher than the minimum concentration that inhibits the growth of other microorganisms.[ ...]

Advances in the creation of computer technology provided the basis for rapid mathematical processing of data on the relationship and remoteness of organisms. The application of this technique to bacterial taxonomy has been called numerical taxonomy and has been introduced into microbiology in recent years. Numerical taxonomy considers the grouping and identification of organisms, taking into account their similarity in the analysis of at least 50-60 objective signs. This method with the development of similarity and differentiation schemes has already been used by a number of authors for systematics. various kinds spore-bearing bacteria.[ ...]

According to morphology, the nature of movement, the method of reproduction and the structure of cells, a number of representatives of colorless sulfur bacteria, both multicellular and unicellular (Beggiatoa, Thiothrix, Thiospirillopsis, Thioploca, Achromatium) show great similarity with blue-green algae. Some researchers, in particular Pringsheim (Pringsheim, 1963), consider these microorganisms as their colorless variants. The blue-green algae Oscillatoria, Thiothrix - Rivularia, Thiospirillopsis - Spirulina are considered to be analogues of Beggiatoa, and Achromatium is similar to Synecho-coccus. Since blue-green algae are now classified as bacteria, their rapprochement with colorless sulfur bacteria is becoming more and more justified. It should also be noted that some blue-green algae have the ability to deposit sulfur in cells, although this feature alone does little for the systematics of microorganisms.[ ...]

Structure and biology of blue-green algae. Cyanophycea, or blue-green algae, are characterized by a peculiar cell color with shades from olive green to bluish green, blue, brown, and sometimes almost black. The structure of these pigments is discussed in the corresponding section of this chapter. Photosynthesis with cyanophycea is accompanied by the release of oxygen. Blue-green algae - Cyanophyta are very similar in cell structure, thallus and a number of biological features with bacteria. Their systematic position in connection with this was repeatedly revised. In the 8th edition of Bergi's 1974 guide to bacteria, they are called cyanobacteria, and are singled out in an independent division, Division Cyanobacteria. All other prokaryotic organisms make up Division II, Division II - Bacteria. Stanier's guide gives brief information about cyanobacteria on just one page, but neither a description of known taxa nor systematics is given.[ ...]

Participation in sporogenesis a large number enzymes and antigens, the inclusion of new biosynthetic pathways and the emergence of new specific cell structures shows that the number of genes controlling sporogenesis is quite large (probably more than 100). Some of these genes also function during the vegetative stage of development. The mechanism of functioning of the spore genome (the set of genes responsible for spore formation) still remains unclear. It has been established that spores receive all their nuclear material (DNA) ready-made from mother cells. At the same time, the amount of DNA per spore is constant for a given species and does not depend on the growing environment of bacteria. Thus, this indicator can probably serve as a characteristic of the species and be used in the taxonomy of spore-forming bacteria.