Bacteria that for their growth and development. The most important bacterial growth factors
One of the manifestations of the vital activity of microorganisms is their growth and reproduction.
Growth is an increase in the size of an individual.
Reproduction is the ability of an organism to reproduce.
The main method of reproduction in bacteria is transverse division, which occurs in different planes with the formation of diverse combinations, cells (clusters, chains, bales, etc.). In bacterial cells, division is preceded by duplication of maternal DNA. Each daughter cell receives a copy of the mother's DNA. The division process is considered complete when the cytoplasm of the daughter cells is separated by a septum. Cells with a dividing septum diverge as a result of the action of enzymes that destroy the core of the septum.
The rate of reproduction of bacteria is different and depends on the type of microbe, the age of the culture, the nutrient medium, and the temperature.
When growing bacteria in a liquid nutrient medium, several phases of culture growth are observed:
1. Phase initial (latent) - microbes adapt to the nutrient medium, the cell size increases. By the end of this phase, bacteria begin to multiply.
2. The phase of logarithmic incubation growth - there is an intensive division of cells. This phase lasts about 5 hours. Under optimal conditions, a bacterial cell can divide every 15-30 minutes.
3. Stationary phase - the number of newly appeared bacteria is equal to the number of dead ones. The duration of this phase is expressed in hours and varies depending on the type of microorganisms.
4. Phase of death - characterized by cell death under conditions of depletion of the nutrient medium and the accumulation of metabolic products of microorganisms in it.
5h 10 15 20 25 30 35 40 45 Time week week
If the nutrient medium in which the microorganisms are cultivated is renewed, the logarithmic growth phase can be maintained.
When multiplying on dense nutrient media, bacteria form colonies typical for each microbial species on the surface of the medium and inside it. Colonies may be convex or flat, with even or uneven edges, with a rough or smooth surface, and may vary in color from white to black. All these features (cultural properties) are taken into account when identifying bacteria, as well as when selecting colonies to obtain pure cultures. To know how to obtain a pure culture of a particular microorganism, one must carefully read the practical part of this chapter.
§ 5. Pigment formation in bacteria
The formation of pigments occurs with good access to oxygen and a certain composition of the nutrient medium. According to the chemical composition and properties, pigments are heterogeneous and are divided into:
Soluble in water (pyocyanins of Pseudomonas aeruginosa);
Soluble in alcohol;
Insoluble in water;
Insoluble in water and alcohol.
Bacteria can form pigments of different colors:
red - Serratia marcescens; cream - Staphilococcus aureus; yellow - Scifreus; blue - Pseudomonas aeruginosa, etc.
Pigments of bacteria protect them from natural ultraviolet radiation, participate in the processes of respiration, synthesis reactions, and have an antibiotic effect.
Photogenic bacteria, i.e., bacteria that can glow, are a kind of form of energy release during oxidative processes. The stronger the influx of oxygen, the stronger the glow of bacteria.
Luminous bacteria are called "photobacteria". These include a large group of physiologically similar but morphologically distinct bacteria (cocci, bacilli, vibrios). They are non-spore-forming vibrios. Most of the species of luminous bacteria are isolated from sea water; they do not cause decay, they are cultivated in ordinary environments. From some bacteria, extracts were obtained that emit light in a dark room, from some extracts, luciferin and the enzyme luciferase were isolated.
A typical representative of photogenic microbes Photobacterium phosphoreum is an immobile coccoid bacterium that develops at a temperature of 28 °C.
No species pathogenic for humans have been identified in the group of photogenic bacteria.
Aroma-forming microbes are microorganisms that have the ability to release volatile substances produced by them in the process of life. They form acetic-ethyl and acetic-amyl esters.
The aromatic properties of wines, dairy products, soil, hay and other substances depend on the activity of certain types of microorganisms. Dairy products, especially butter, are aromatic due to the bacterium Teisonostos cremoris.
With the help of microbes, methane is obtained by fermenting manure, plant residues and household waste, which is used in many countries for space heating.
Industrial enterprises have already begun to produce microbial protein used for animal and bird feed. With the help of microbes, you can get vitamins, enzymes (amylase, lactose, penicillinase, proteases.)
Pathogenic representatives produce substances that are toxic to humans and animals - toxins, which are divided into 2 groups:
1. Exotoxin - proteins that the cell secretes into the external environment, has pronounced immunogenic and antigenic properties. Often they consist of two fragments - A and B. The B-fragment promotes adhesion, invasion. A - has a pronounced activity in relation to the internal systems of the cell.
2. Endoxin - is closely associated with the body of the microbial cell, as it is localized in the lipopolysaccharide layer of the cell wall. The action of endoxins on the body is not specific. Endoxins are released when the microbial cell is destroyed.
More information about the properties of toxins can be found in the chapter "The Doctrine of Infection".
Bacterial activity is characterized by growth- the formation of structural and functional components of the cell and the increase in the bacterial cell itself, as well as reproduction-- self-reproduction, leading to an increase in the number of bacterial cells in the population.
bacteria multiply by binary fission in half, less often by budding. Actinomycetes, like fungi, can reproduce by spores. Actinomycetes, being branching bacteria, reproduce by fragmentation of filamentous cells. Gram-positive bacteria divide by growing the synthesized division partitions into the cell, and gram-negative bacteria divide by constriction, as a result of the formation of dumbbell-shaped figures, from which two identical cells are formed.
Cell division preceded replication of the bacterial chromosome according to a semi-conservative type (the double-stranded DNA chain opens and each strand is completed by a complementary strand), leading to the doubling of the DNA molecules of the bacterial nucleus - the nucleoid.
DNA replication occurs in three stages: initiation, elongation, or chain growth, and termination.
Reproduction of bacteria in a liquid nutrient medium. Bacteria seeded in a certain, unchanging volume of the nutrient medium, multiplying, consume nutrients, which subsequently leads to the depletion of the nutrient medium and the cessation of bacterial growth. The cultivation of bacteria in such a system is called periodic cultivation, and the culture is called periodic. If the cultivation conditions are maintained by continuous supply of fresh nutrient medium and the outflow of the same volume of culture fluid, then such cultivation is called continuous, and the culture is called continuous.
When growing bacteria on a liquid nutrient medium, near-bottom, diffuse, or surface (in the form of a film) culture growth is observed. The growth of a periodic culture of bacteria grown on a liquid nutrient medium is divided into several phases, or periods:
- 1. lag phase;
- 2. phase of logarithmic growth;
- 3. phase of stationary growth, or maximum concentration
bacteria;
4. phase of bacterial death.
These phases can be depicted graphically as segments of the bacterial reproduction curve, which reflects the dependence of the logarithm of the number of living cells on the time of their cultivation.
Lag phase- the period between sowing bacteria and the beginning of reproduction. The duration of the lag phase is on average 4-5 hours. Bacteria increase in size and prepare for division; the amount of nucleic acids, protein and other components increases.
Logarithmic (exponential) growth phase is a period of intensive division of bacteria. Its duration is about 5-6 hours. Under optimal growth conditions, bacteria can divide every 20-40 minutes. During this phase, bacteria are the most vulnerable, which is explained by the high sensitivity of the metabolic components of a rapidly growing cell to inhibitors of protein synthesis, nucleic acids, etc.
Then comes the stationary growth phase., at which the number of viable cells remains unchanged, constituting the maximum level (M-concentration). Its duration is expressed in hours and varies depending on the type of bacteria, their characteristics and cultivation.
The death phase completes the process of bacterial growth, characterized by the death of bacteria in conditions of depletion of the sources of the nutrient medium and the accumulation of metabolic products of bacteria in it. Its duration varies from 10 hours to several weeks. The intensity of growth and reproduction of bacteria depends on many factors, including the optimal composition of the nutrient medium, redox potential, pH, temperature, etc.
Reproduction of bacteria on a dense nutrient medium. Bacteria growing on dense nutrient media form isolated rounded colonies with even or uneven edges (S- and R-forms), of different consistency and color, depending on the bacterial pigment.
Water-soluble pigments diffuse into the nutrient medium and color it. Another group of pigments is insoluble in water but soluble in organic solvents. And, finally, there are pigments that are insoluble neither in water nor in organic compounds.
The most common pigments among microorganisms are carotenes, xanthophylls, and melanins. Melanins are insoluble black, brown or red pigments synthesized from phenolic compounds. Melanins, along with catalase, superoxide cismutase, and peroxidases, protect microorganisms from the effects of toxic oxygen peroxide radicals. Many pigments have antimicrobial, antibiotic-like effects.
Bacteria growth- this is an increase in the number, mass and size of all microbial cells, starting immediately after its division. Growth is inextricably linked with reproduction.
Reproduction in bacteria– the process of self-reproduction of a microbial cell. It begins with the division of the nucleoid DNA into two daughter strands, each of which is then completed with a complementary strand, while the formation of two daughter cells occurs simultaneously (semi-conservative method). bacteria multiply transverse division a sharp increase in the number of cells in the population, the process is repeated at regular intervals (from several minutes to several days), being an individual genetic characteristic of the microbial species. During division, either two identical cells or two asymmetric (polymorphic) cells can be formed.
Bacteria are distinguished by a high rate of reproduction on various nutrient media, which is characterized by the generation time. This is the time between two cell divisions, passing from the moment the cell appears to the moment of division (for example, the generation time of Escherichia coli is 20 minutes, the causative agent of tuberculosis is 14 hours). The rate of reproduction depends on the type of bacteria and cultivation conditions (the chemical composition of the nutrient medium, its state of aggregation, pH, temperature, aeration, gas composition, the presence of nutrients and growth stimulants, etc.). When bacteria multiply on dense nutrient media, they form colonies- offspring of one cell, visually determined on (or in) a nutrient medium. Isolated colonies are accumulations of microbes of the same species, and, as a rule, one clone.
Appearance of the colonies in some bacteria it can be very peculiar, being typical for some microorganisms. For example, colonies of the anthrax agent are compared with a “lion's mane” or “jellyfish's head”, plague colonies are similar to a “lace scarf”, etc.
To characterize colonies growing on nutrient media, a number of standard parameters are used - macroscopic characteristic .
In the form of a colony there are regular - rounded, or irregular - amoeboid and rhizoid, resembling intertwining tree roots. Depending on the size, colonies are punctate (diameter less than 1 mm), small (diameter I - 2 mm), medium (diameter 2 - 4 mm) and large (diameter 4 - 6 mm or more).
Colour determined by the type of pigment (white, yellow, red, etc. - Fig. 25 - Appendix). Pigmented colonies, for example, are found in staphylococcus aureus (white, lemon yellow or golden), in sarcinas the color of the pigment is yellow, in bacteria of the genus Serratia red, in yeast-like fungi candida albicans white. Many pathogenic bacteria do not form pigment - their colonies are transparent or opalescent.
By consistency colonies of bacteria are more often soft, mucous or dense, crumbly. By the nature of the regions Distinguish between smooth edges in the form of a clearly defined line and uneven - scalloped and wavy. Surface colonies are matte or shiny with gloss, dry or wet, smooth or rough. Smooth colonies are denoted by the letter S (smooth - smooth), rough by the letter R (rough - rough).
When growing bacteria on a liquid nutrient medium, a successive change of individual phases in the reproduction of the bacterial population is observed (Fig. 9):
1. Initial phase (lag phase). Cell reproduction does not occur; microbes adapt to the nutrient medium, increase in size, accumulate enzymes, DNA replication begins. At the end of the phase, the slow multiplication of microbes begins.
2. Exponential phase (log phase) characterized by the maximum rate of reproduction, while the number of bacteria increases exponentially.
3. stationary phase, at which there is a balance between the number of newly formed cells and the number of dead ones.
4. Dying phase. During this phase, cell death occurs.
The value of biomass is determined by its dry weight, as well as the content of bacterial nitrogen, protein, DNA, and phosphorus.
Microorganisms, like other living beings, are characterized by growth and reproduction. Cell growth is understood as a coordinated increase in the amount of all chemical components (for example, protein, RNA, DNA), leading, ultimately, to an increase in the size and mass of the cell. The growth of a microbial cell is not unlimited, having reached a certain value, the cell stops growing and begins to multiply.
Reproduction is an increase in the number of microorganism cells in a Population. Microorganisms reproduce either by transverse division, which occurs during growth, or by budding (which is extremely rare), or by the formation of spores.
Prokaryotes usually reproduce asexually by binary fission. At the beginning of cell division, the cell elongates, then the nucleoid divides. The reproduction of a nucleoid containing all the genetic information necessary for the life of a microorganism is the most important of all the processes that occur during cell growth.
The nucleoid is represented by a supercoiled and very densely packed DNA molecule, which is a self-replicating structure and is known as a replicon. Replicons also include plasmids - genetic structures capable of self-replication. DNA replication is carried out by DNA polymerase enzymes. This process starts at a certain point in the DNA and proceeds simultaneously in two opposite directions. Replication also takes place in a certain place of DNA - As a result of replication, the number of DNA molecules in a cell doubles. The newly synthesized DNA molecules gradually diverge into the resulting daughter cells. All this allows the daughter cell to have a DNA molecule completely identical to the mother cell in the nucleotide sequence. It is believed that the replication of the DIC takes almost 80% of the time during which the division of the bacterial cell is carried out.
After completion of DNA replication, a complex set of processes begins that lead to the formation of an intercellular septa. Initially, two layers of the cytoplasmic membrane grow on both sides of the cell, and then peptidoglycan is synthesized between them and a septum is formed, consisting of two layers of the cytoplasmic membrane and peptidoglycan.
During DNA replication and the formation of a dividing septum, the cell of the microorganism continuously grows. During this period, the synthesis of peptidoglycan of the cell wall, the cytoplasmic membrane, the formation of new ribosomes and other organelles and compounds that are part of the cytoplasm take place. At the last stage of division, daughter cells separate from each other. The process of division in some bacteria does not go to the end, as a result, chains of cells are formed.
When rod-shaped bacteria divide, the cells first grow in length (the diameter of the cell does not change). When the bacterium doubles in length, the rod narrows somewhat in the middle and then splits into two cells. Most often, the cell is divided into two equal parts (isomorphic division), but uneven (heteromorphic) division also occurs when the daughter cell is larger than the mother cell.
Figure 25 shows the division of a bacterium with flagella. Only the mother cell has flagella. The daughter cell does not have flagella: they grow later. In numerous studies, flagella were usually found in only one cell from a recently separated pair. It can be assumed that the mother cell retains the main part of the original cell wall, fibria and flagella.
Spirochetes, rickettsiae, some yeasts and fungi, protozoa and other organisms reproduce by transverse cell division.
Myxobacteria divide by constriction. First, the cell narrows slightly at the site of division, then the cell wall, gradually protruding from both sides into the cell, narrows it more and more and, finally, divides it into two. The daughter cell, already clothed with its own cytoplasmic membrane, still temporarily retains a common cell wall.
Bacteria sometimes have a "sexual" process, or conjugation (see Chapter 4).
As a result of the growth and reproduction of a microorganism cell, a colony of microbes is formed - descendants.
Microorganisms are characterized by a high rate of reproduction, expressed in the generation time, that is, the time during which cell division occurs. The generation time is determined by the type of microorganism, its age, and external conditions (composition of the nutrient medium, temperature, pH, and other factors).
Under favorable conditions, the generation time of many microorganisms ranges from 20 to 30 minutes. With this growth rate, 6 generations can be obtained in 2 hours (it takes 120 years to obtain the same number of generations in a person). Due to the ability of bacteria to multiply rapidly, in nature their numerical superiority over other living organisms is observed. However, bacteria cannot continue to grow for a very long time with a generation period of 20 min. If such growth were possible, then one - the only cell of E. coli (Escherichia coli) after 24 hours would form 272, or about 1022 descendants, the total mass of which would be several tens of thousands of tons, and after another 24 hours of growth of this bacterium, its mass descendants would exceed several times the mass of the globe. The lack of food, and the accumulation of decay products, limit such rapid growth of bacteria. In a flowing medium, bacteria can divide every 15-18 minutes.
Observations of the growth of microorganisms cultivated in a liquid medium in closed tanks show that the rate of their growth varies with time. Microorganisms introduced into the nutrient medium do not develop at first, they "get used" to environmental conditions. Then their reproduction begins with an ever-increasing rate, reaching the maximum that they are capable of in a given environment. As nutrients are depleted and metabolic products accumulate, growth slows down and then stops completely. The development cycle of bacteria consists of several phases (Fig. 26).
I. The initial (stationary) phase begins after the introduction of microorganisms into the nutrient medium and lasts from 1 to 2 hours. During this phase, the number of bacteria does not increase, and the cells do not grow.
II. Lag - phase - a period of delay in reproduction. At this time, the bacteria introduced into the fresh nutrient medium begin to grow rapidly, but the rate of their division remains low.
The first two phases of the development of a bacterial population are called the period of adaptation to a new environment. By the end of the lag phase, cells often increase in volume. The duration of the lag phase depends both on external conditions and on the age of bacteria and their species specificity.
III. The phase of intensive logarithmic, or exponential, reproduction. During this period, bacteria multiply at the highest rate, and the number of cells increases exponentially.
IV. In the phase of negative acceleration, bacterial cells become less active, and the generation period begins to lengthen. One of the reasons that slow down the reproduction of bacteria is the depletion of the nutrient medium and the accumulation of poisonous (toxic) metabolic products in it. This slows down the rate of reproduction. Some cells stop multiplying and die.
V. Stationary phase - the period when the number of newly emerging cells is approximately equal to the number of dying ones. Therefore, the number of living cells remains practically unchanged for some time. However, at the same time, the total number of living and dead bacteria somewhat increases, although not so rapidly. This phase is sometimes called the "maximum stationary" phase, since it is during this phase that the number of cells in the medium reaches its maximum.
VI-VIII. The dying phases are characterized by the fact that cell death prevails over reproduction. During the passage of phase VI, the number of dead cells increases. This phase is replaced by VII - logarithmic cell death, when they die off at a constant rate. Finally, phase VIII sets in, in which the rate of death of bacterial cells gradually decreases. The death of cells of the bacterial population in the last three phases is associated with a change in the physicochemical properties of the nutrient medium in an unfavorable direction for bacteria and with other reasons. The rhythm of cell death in these phases becomes rapid, and the number of living cells decreases more and more, until they almost completely die.
In the closed tank culture described above, the microorganisms are constantly under changing conditions, this is the so-called stagnant culture of microorganisms. At first they have all the nutrients in abundance, then gradually there is a lack of nutrition and poisoning with metabolic products. All this leads to a decrease in the growth rate, as a result of which the culture passes into the stationary phase. However, if nutrients are added to the medium and metabolic products are removed at the same time, then microorganisms could remain in the exponential growth phase for an indefinite time. This method underlies the flow cultivation of microorganisms, carried out in chemostats and turbidostats using special devices for continuous supply of the medium at a controlled rate and for its good mixing.
Therefore, in contrast to non-flow culture, constant conditions are created for microorganisms in flow culture. Therefore, continuous and constant cell growth can be maintained at any culture growth rate. The flow cultivation of microorganisms is amenable to automatic control, it is very promising and is widely introduced into industry and laboratory practice.
In physiological studies of microorganisms, it is important to obtain so-called synchronous cultures. Synchronous culture is a bacterial culture (or population) in which all cells are at the same stage of the cell cycle. Synchronous cultures are usually used to study individual bacteria as they grow.
In order to study microorganisms, determine the etiological factors of infectious diseases, deal with the prevention and treatment of infectious diseases, and solve many other issues related to microorganisms, it is necessary to have enough of them, which means creating all conditions for the normal growth and reproduction of microorganisms.
The term "reproduction" of microbes means their ability to self-reproduce, to increase the number of individuals.
Reproduction of microorganisms occurs by transverse division, budding, spore formation, reproduction.
The growth of microorganisms means an increase in the mass of microbes as a result of the synthesis of cellular material and the reproduction of all cellular components and structures.
Bacteria, spirochetes, actinomycetes, fungi, rickettsiae, mycoplasmas, protozoa, chlamydia are said to reproduce, while viruses and phages (microbial viruses) reproduce.
The reproduction of microorganisms corresponds to certain patterns. The rate of division of microorganisms is different, it depends on the type of microbe, the age of the culture, the characteristics of the natural and artificial nutrient medium, temperature, carbon dioxide concentration and many other factors.
In the process of reproduction, microorganisms undergo morphological and physiological changes at various stages (in shape, size, staining, biochemical activity, sensitivity to physical and chemical factors, etc.).
Microorganisms have age-related variability, i.e. individuals change at different stages of growth, maturation and aging. These changes are observed in the normal cycle of the individual development of a microorganism, which depends on the nature of the organism, on the complexity of its structure and sequence in development.
Bacteria have the simplest cycle of development among microorganisms. They reproduce by simple transverse division in different planes. Depending on this, cells can be arranged randomly, in clusters, chains, packages, in pairs, in fours, etc.
A characteristic feature of bacteria, which distinguishes them from numerous animals and plants, is their extraordinary rate of reproduction.
Each bacterial cell, on average, undergoes division within half an hour, which is due to increased metabolism, the speed with which the nutrient material enters the cell.
The factor inhibiting the reproduction of bacteria is the depletion of the nutrient substrate and the poisoning of the environment by decay products.
There are eight main phases of reproduction in bacteria.
1. The initial stationary phase, which is a period of time of one to two hours from the moment of sowing bacteria on a nutrient medium. No reproduction occurs during this phase.
2. The phase of reproduction delay (lag - phase), during which the reproduction of bacteria occurs very slowly, and their growth rate increases. The duration of the second phase is about two hours.
3. The phase lasts five to six hours. The third phase is characterized by the maximum rate of division, a decrease in cell size.
4. Phase of negative acceleration (lasts about two hours). The rate of reproduction of bacteria decreases, the number of dividing cells decreases.
5. Stationary phase, lasting about two hours. The number of new bacteria is almost equal to the number of dead individuals.
6. Phase of cell death acceleration (lasts about three hours).
7. Phase of logarithmic cell death (lasts about five hours), in which cell death occurs at a constant rate
8. Phase of decrease in the rate of death. The surviving individuals go into a state of rest.
The duration of the breeding phases is not a constant value. It can be different depending on the type of microorganisms and cultivation conditions.
The development cycle of coccoid bacteria is reduced to the growth of the cell and its subsequent division. Rod-shaped asporogenic bacteria grow at a young age, reach a maximum size, then divide into two daughter cells, which repeat the same cycle. In bacilli and clostridia, the process of spore formation is included in the development cycle under certain conditions.
Spirochetes and rickettsia, like bacteria, reproduce by binary fission.
Among mycoplasmas, all elementary bodies of a spherical or ovoid shape have the ability to reproduce. In the process of development, several filamentous outgrowths appear on the elementary body, in which spherical bodies are formed. Gradually, the threads become thinner and chains are formed with clearly defined spherical bodies. Then the threads are divided into fragments and the spherical bodies are released.
Reproduction of some mycoplasmas occurs by budding of daughter cells from larger spherical bodies. Mycoplasmas reproduce by transverse fission if the processes of mycoplasma division proceed synchronously with the replication of the nucleoid DNA. In case of violation of synchrony, filamentous multinucleoid forms are formed, subsequently dividing into coccoid cells.
Actinomycetes and fungi have two different stages of development: the stage of vegetative growth, in which the formation of mycelium is characteristic, and the stage of formation of spores that form on sporophores.
An important feature of actinomycetes and fungi is a significant variety of ways of their reproduction. They are characterized by vegetative, asexual and sexual reproduction.
Vegetative propagation is carried out by dividing into fragments of hyphae, followed by the formation of individual rod-shaped and cocci-shaped cells.
Asexual reproduction occurs vegetatively (growth of fragments of hyphae or their individual cells) and with the help of more or less specialized reproductive organs (spores and conidia). The most frequent, asexual, way of reproduction is manifested in the formation of exogenous and endogenous spores. Exospores or conidia are formed at the ends of fruiting hyphae, but are enclosed within a common sac - sporangia. Hyphae that carry sporangia are called sporangiophores. Sporangiophores can be straight, wavy, spiral.
Sexual reproduction occurs with the help of special organs - ascospores, basidiospores, the formation of which is preceded by the sexual process. According to the biological purpose, spores of actinomycetes and fungi are dormant, serving to preserve the species for a certain period and serving for rapid reproduction.
Spores of actinomycetes and fungi are formed by each individual in large numbers, since, unlike spores of bacteria, they serve mainly for the purposes of reproduction. They are less resistant to environmental factors than bacterial spores.
In protozoa, as well as in actinomycetes and fungi, along with reproduction by division, there is also a sexual process.
Chlamydia, viruses and phages have peculiar cycles of development.
Reproduction of chlamydia begins with the penetration of elementary bodies into a sensitive tissue cell by endocytosis. These bodies in the vacuole of the cell turn into vegetative forms, called initial or reticular bodies, which have the ability to divide. Reticular bodies have a lamellar cell wall, and in the cytoplasm there are loosely located nuclear fibrils and numerous ribosomes. After repeated division, the reticular bodies turn into intermediate forms, from which a new generation of elementary bodies develops. The whole cycle of development of chlamydia lasts 40-48 hours and ends with the formation of a microcolony of chlamydia in the cytoplasm of the host cell.
After the rupture of the vacuole wall and the complete destruction of the host cell, the microcolonies of chlamydia, being outside the whole cell, break up into independent elementary bodies, and the cycle of penetration of chlamydia into the cell with their subsequent reproduction is repeated.
The reproduction of viruses is characterized by a sequence of individual stages.
1. Stage of adsorption. Virions are adsorbed on the surface structures of the cell. In this case, the interaction of complementary structures of the virion and the cell, which are called receptors, occurs.
2. The stage of penetration of the virion into the host cell. The ways of introduction of viruses into cells sensitive to them are not the same. Many virions enter the cell by pinocytosis, when the resulting pinocytic vacuole "pulls" the virion into the cell. Some viruses enter the cell directly through its membrane.
3. The stage of destruction of the outer shell and capsid of the virion with the help of proteolytic enzymes of the host cell. In some virions, the process of destruction of their shell begins at the stage of adsorption, in others - in the pinocytic vacuole, in others - directly in the cytoplasm of the cell with the participation of the same proteolytic enzymes.
4. Stage of viral protein synthesis and nucleic acid replication. After the complete or partial release of the viral nucleic acid, the process of viral protein synthesis and nucleic acid replication begins.
5. Assembly stage or virion morphogenesis. The formation of virions is possible only under the condition of a strictly ordered connection of viral structural polypeptides and their nucleic acid, which is ensured by the self-assembly of protein molecules around the nucleic acid. In some viruses, this process occurs in the cytoplasm, in others, in the nucleus of the host cell. In complexly organized viruses with an outer shell, further assembly occurs in the cytoplasm during their release from the cell.
6. The stage of release of virions from the host cell. A number of complex viruses leave the host cell, while the cells remain viable for some time, and then die. Simple virions leave the cell through the holes formed in its shell, the host cell dies, not maintaining viability for some time.
In some cases, the reproduction of virions in cells can occur over many months and even years. Viruses are shed through the cell wall. When such cells divide, the virions are transferred to daughter cells, which in turn begin to produce viral particles.
There are three types of interaction between a virus and a cell: productive, abortive, and virogenic.
Productive the type of interaction is the formation of new virions.
Abortive the type of interaction can be abruptly interrupted at the stage of viral nucleic acid replication or viral protein synthesis, or virion morphogenesis.
Virogenic the type is characterized by the incorporation (integration) of the viral nucleic acid into the DNA of the cell, which ensures synchronous replication of the viral and cellular DNA.
During phage reproduction, it is also adsorbed on the cell surface (stage 1) as a result of the interaction of amino groups of proteins localized in the peripheral part of the phage tail process and negatively charged carboxyl groups on the surface of the bacterial cell.
There are reversible and irreversible phases of adsorption. The reversible phase is characterized by the fact that fixed phages can be separated from the cell by vigorous agitation or the concentration of ions can be sharply reduced. The released phages retain their viability.
During the second irreversible phase of adsorption, the phage does not separate from the microbial cell body. The adsorption process takes several minutes. Under the influence of an enzyme located in the tail process of the phage, a hole is formed in the body of the microbial cell at the site of attachment of the phage, through which the phage DNA penetrates into the cell. The phage shell remains outside (stage 2).
Some phages introduce their nucleic acid into the cell without prior mechanical damage to the cell wall. During the latent period following the penetration of the phage nucleic acid into the cell, the biosynthesis of the phage nucleic acid and phage capsid proteins takes place.
There is a synthesis of enzymes necessary for the replication of phage nucleic acid and structural proteins of the phage (stage 3).
In the fourth stage, the hollow phage particles are filled with the phage nucleoacid and mature phages are formed. Phage morphogenesis is carried out.
At the end of the latent period, the infected microbial cells are lysed and mature phage particles are released (stage 5).
It is believed that the adsorption of the phage lasts 40 minutes, the latent period is 75 minutes. The entire cycle of interaction between a phage and a microbial cell lasts a little more than three hours.
The introduction of a phage into a microbial cell is not always accompanied by its lysis. Often, the interaction of a phage with a microbial cell leads to the formation of lysogenic cultures.
By the nature of the interaction with the microbial cell, temperate and virulent phages are distinguished. The state of lysogeny is caused by temperate phages. Lysogenic microbial cells are resistant to virulent phages. Virulent phages cause the formation of new phages and the lysis of the microbial cell.
