Stages of microorganism reproduction. Growth and reproduction of bacteria

Growth and reproduction of bacteria. Mechanism and speed of reproduction. Phases of microbial reproduction.

1. Concepts of bacterial growth and reproduction

2. Bacterial population

3.Colonies

1 . For microbiological diagnostics, study of microorganisms and for biotechnological purposes microorganisms are cultivated on artificial nutrient media.

Under bacterial growth understand increase in cell mass without changing their number in the population as a result of the coordinated reproduction of all cellular components and structures.
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Increasing the number of cells in a population of microorganisms denoted by the term "reproduction". It is characterized generation time(the time interval during which the number of cells doubles) and such a concept as bacteria concentration(number of cells in 1 ml).

In contrast to the mitotic division cycle in eukaryotes, the reproduction of most prokaryotes (bacteria) occurs by binary fission, and actinomycetes - budding. However, all prokaryotes exist in a haploid state, since the DNA molecule is represented in the cell in the singular.

2. When studying the process of bacterial reproduction, it is extremely important to consider that bacteria always exist in the form of more or less numerous populations, and development bacterial population in a liquid nutrient medium in batch culture can be considered as closed system.

There are 4 phases in this process:

‣‣‣ 1st - initial, or lag phase or reproductive delay phase - characterized the beginning of intensive cell growth, But the rate of their division remains low;

‣‣‣ 2nd - logarithmic or log phase, or exponential phase, - characterized constant maximum rate of cell division and a significant increase in the number of cells in the population;

‣‣‣ 3rd - stationary phase - comes when the number of cells in the population stops increasing. This is due to the fact that an equilibrium occurs between the number of newly formed and dying cells. The number of living bacterial cells in a population per unit volume of nutrient medium in the stationary phase is denoted as M-concentration. This indicator is a characteristic feature for each type of bacteria;

‣‣‣ 4th - die-off phase (logarithmic death) - characterized a predominance in the population of the number of dead cells and a progressive decrease in the number of viable cells in the population. The cessation of growth in the number (reproduction) of a population of microorganisms occurs due to the depletion of the nutrient medium and/or the accumulation of metabolic products of microbial cells in it. For this reason, by removing metabolic products and/or replacing the nutrient medium, regulating the transition of the microbial population from the stationary phase to the dying phase, it is possible to create open biological system seeking to eliminate dynamic equilibrium at a certain level of population development.

This process of growing microorganisms is commonly called flow cultivation (continuous culture). Growth in a continuous culture makes it possible to obtain large masses of bacteria during flow cultivation in special devices (chemostats and turbidistats) and is used in the production of vaccines, as well as in biotechnology for the production of various biologically active substances produced by microorganisms.

To study metabolic processes throughout the cell division cycle, it is also possible to use synchronous cultures - such bacterial cultures, all members of the population of which are in one phase of the cycle. This is achieved using special cultivation methods.

In this case, after several simultaneous divisions, the synchronized cell suspension gradually switches back to asynchronous division, so that the number of cells subsequently increases not stepwise, but continuously.

3. When cultivated on solid nutrient media, bacteria form colonies - a cluster of bacteria of the same species visible to the naked eye, which is most often the offspring of one cell.

Colonies of bacteria of different species are different:

‣‣‣ shape;

‣‣‣ size;

‣‣‣ transparency;

‣‣‣ color;

‣‣‣ height;

‣‣‣ the nature of the surface and edges;

‣‣‣ consistency.

The nature of the colonies - one of the taxonomic characteristics of bacteria.

44. Definition and essence of the concepts “biosphere” and “biocenosis”. Modern ideas about the evolution of microbes.

In nature, microorganisms inhabit almost any environment (soil, water, air) and are much more widespread than other living beings. Due to the variety of mechanisms for recycling food and energy sources, as well as pronounced adaptation to external influences, microorganisms can live where other forms of life cannot survive.

The natural habitats of most organisms are water, soil and air. The number of microorganisms living on plants and in animal bodies is much smaller.

The wide distribution of microorganisms is associated with the ease of their spread through air and water; in particular, the surface and bottom of freshwater and salt water bodies, as well as several centimeters of the top layer of soil, are replete with microorganisms that destroy organic matter. A smaller number of microorganisms colonize the surface and some internal cavities of animals (for example, the gastrointestinal tract, upper respiratory tract) and plants. In habitat areas, microorganisms form biocenoses [from Greek bios, life, + koinos, community] - complex associations with specific and often unusual relationships. Each microbial community in a specific biocenosis forms specific autochthonous microorganisms [from Greek autos yours, + chthon,

country, locality], that is, microbes inherent in a specific area. biocenoses Symbiosis symbiosis , cohabitation] - the long-term coexistence of microorganisms in long-lived communities. The relationship in which a microorganism is located outside the cells of the host (larger organism) is known as ectosymbiosis: when localized inside cells, it is known as endosymbiosis. Typical ectosymbiotic microbes - Escherichia coli bacteria genera Bacteroides And Bifidobacterium, Proteus vulgaris,

as well as other representatives of intestinal microflora. As an example of endosymbiosis, we can consider plasmids that provide, for example, bacterial resistance to drugs. Symbiotic relationships are also divided according to the benefits received by each partner. Mutualism [from lat. mutual] - mutually beneficial symbiotic relationship. Thus, microorganisms produce biologically active substances necessary for the host body (for example, B vitamins). At the same time, endo- and ectosymbionts living in macroorganisms are protected from unfavorable environmental conditions (drying and extreme temperatures) and have constant access to nutrients. Of all the types of mutualism, the most surprising is the cultivation of some fungi by insects (beetles and termites). On the one hand, this contributes to a wider distribution of fungi, on the other - o\

mj provides a constant source of nutrients for the larvae. This is reminiscent of human cultivation of useful plants and microorganisms.

Commensalism- a type of symbiosis in which only one partner benefits (without causing “visible” harm to the other); microorganisms involved in such relationships are commensals [from lat. cell-, s, + mensa, table; literally - table mates]. Commensal microorganisms colonize the skin and cavities of the human body (for example, the gastrointestinal tract), without causing “visible” harm; their totality is normal microbial flora (natural microflora). Typical ectosymbiotic commensal organisms are Escherichia coli, bifidobacteria, staphylococci, and lactobacilli. Many commensal bacteria belong to opportunistic microflora and are capable, under certain circumstances, of causing diseases of the macroorganism (for example, when they are introduced into the bloodstream during medical procedures).

Growth and reproduction of bacteria. Mechanism and speed of reproduction. Phases of microbial reproduction. - concept and types. Classification and features of the category "Growth and reproduction of bacteria. Mechanism and speed of reproduction. Phases of microbial reproduction." 2017, 2018.

Cells, like any living organism, are born, live and die. The growth and reproduction of bacteria occurs very quickly; they could take over all living space on the planet if not for their fragility and limiting factors (temperature, acidity level, lack of food, etc.). Under favorable conditions, cell doubling takes on average about half an hour. However, in critical situations, some types of microorganisms (spore-forming bacteria) are capable of forming spores and “hibernating” for a fairly long period.

The rapid proliferation of bacteria has its pros and cons. The use of microorganisms in biotechnology (yeast, lactic acid, nitrogen-fixing organisms, molds, etc.) is aimed at improving the quality of life. However, the uncontrolled growth of disease-causing (pathogenic) microbes is dangerous for people. A person’s own microflora can also harm health. In medicine, there is the concept of bacterial overgrowth syndrome, in which the number of opportunistic microbes in the human body increases sharply, which poses a threat to health.

Cell growth and reproduction are two different processes. Growth refers to an increase in cell mass due to the formation of all cellular structures. Reproduction is an increase in the number of cells in a colony. There are binary fission, budding and genetic recombination (a process reminiscent of sexual reproduction).

Most prokaryotic (non-nuclear) cells, to which all bacteria belong, reproduce by dividing into two (binary fission). In this way, for example, lactic acid bacteria reproduce. The process begins with the doubling of the bacterial chromosome (a DNA molecule that replaces the nucleus) and proceeds in several stages:

• the cell lengthens;
• the outer shell “grows” inward and forms a transverse partition (constriction);
• two new (daughter) cells move in different directions.

The result is two identical organisms.

Individual microorganisms divide by budding, but this is rather an exception to the general rule. The process consists of the formation of a short protrusion at one of the poles of the cell, into which one of the halves of the divided nucleoid (DNA molecules with genetic information) “drifts”. The protrusion then grows and separates from the mother cell.

There is another option that resembles sexual reproduction - genetic recombination. In this case, genetic information is exchanged and the result is a cell containing the genes of its parents. There are three ways to transfer genetic information:

• conjugation – direct transfer (not exchange) of a part of DNA upon contact from one bacterium to another (the process occurs in only one direction);
• transduction – transfer of a DNA fragment using a bacteriophage (bacterial virus);
• transformation – absorption of genetic information of dead or destroyed cells from the environment.

Thus, only as a result of binary fission and budding are cells identical to each other obtained. During genetic recombination, the cell undergoes changes, developing new properties and gaining other functions.

Speed ​​and phases of growth of microorganisms

In nutrient media, the growth and reproduction of bacteria occurs in several stages, varying in the amount of available food and the accumulation of waste products:

1. The first phase (latent) is determined by factors of adaptation to the nutrient medium. At this time, microorganisms are just getting used to new conditions. No bacterial growth is observed.
2. The second phase (exponential) is characterized by growth in geometric progression (increase along an exponential curve). During this period, bacterial cells actively grow, using all available food (maximum growth rate). Having reached a certain size, the bacterium begins to divide, and the reproduction process proceeds at a constant speed, since there are still enough food supplies. As a result of the increased rate of growth and reproduction, waste products (toxins) accumulate in the environment. Towards the end of the phase, the growth rate begins to decrease.
3. The third phase is characterized by stationary growth, i.e. the number of “newborn” cells coincides with the number of dead ones. The growth and reproduction curve no longer rises in this segment. The growth rate is slowing down. For some time, the total number of bacteria in the nutrient medium remains unchanged. However, due to the emergence of new “family members,” nutrient reserves decrease and the toxicity of the environment increases. This process worsens the living conditions of the entire colony.
4. The fourth phase - the death of microorganisms - occurs as a result of a catastrophic decrease in food and an increase in the toxicity of the environment. The number of living organisms is steadily decreasing; eventually, there are fewer viable cells than their dead counterparts.

The rate of kinetic growth of a bacterial colony largely depends on the type of bacteria, the composition of the nutrient media, the number of cells seeded (introduced into the medium), the age of the culture, the method of respiration and a number of other factors. For example, for the reproduction of lactic acid bacteria, it is important to maintain temperatures in a fairly narrow range (25-30⁰C) and a certain level of acidity of the environment (pH). For the reproduction of aerobic and anaerobic cells, the decisive factor is the presence or absence of oxygen for respiration, and spore-forming cells need a sufficient amount of food.

Conditions for growing microbes in artificial environments

For study (medicine, microbiology) and use (industry), bacterial cultures are grown on artificial nutrient media, which are divided according to consistency, origin and purpose:

• liquid, semi-liquid and dense (solid) artificial media;
• media of animal, plant or synthetic origin (chemically pure compounds in a strictly defined concentration);
• conventional (universal), differential (differ by type of bacteria), special, selective or enrichment media (suppressing the growth of unwanted microbes).

There are bacteria that require special conditions. For example, anaerobic microorganisms (both spore-forming and non-spore-forming) are cultivated under anaerobic conditions (without oxygen). For aerobic cells, oxygen becomes the decisive factor for reproduction. Facultative anaerobes are able to change the way they breathe depending on conditions. The spore-forming aerobic organisms used to produce probiotics are very sensitive to reduced nutrition and its quality. Spore-forming anaerobes require the complete absence of oxygen. The basic principle of cultivating microorganisms is the creation of favorable conditions (nutrition, breathing, temperature), which sometimes presents certain difficulties.

Thus, to grow anaerobes, the deep sowing method is used, i.e., a bacterial culture is introduced into the depths of a dense nutrient medium, chemicals that absorb oxygen are added to the growth atmosphere, or the air is pumped out, replacing it with an inert gas. In the case of spore-forming bacteria, a protein synthesis inhibitor is added to the nutrient medium, thereby stopping the sporulation process.

Cultivation of microorganisms

Cultivation refers to the artificial growth of cells under controlled conditions. The ultimate goal is to obtain a biological product from bacteria or with the help of bacteria. Such drugs can be therapeutic, diagnostic, or prophylactic. There are several cultivation methods:

1. The stationary method is characterized by a constant environment; there is no interference in the process. However, with this method of cultivation in liquid nutrient media, anaerobic organisms give an insignificant yield.
2. The deep cultivation method is used in industry to grow bacterial biomass. For this purpose, special containers are used. Growth factors are temperature maintenance and the supply of nutrients to liquid media. In addition, if necessary, stirring or oxygen supply is carried out (for the respiration of aerobic bacteria).
3. The flow media method (industrial cultivation) is based on constantly maintaining the culture in the exponential growth phase. This is achieved by the continuous introduction of nutrients and the removal of toxic waste from cells. This technology makes it possible to achieve maximum yield of various biologically active substances (antibiotics, vitamins, etc.).

One of the most important industrial preparations is the culture of lactic acid bacteria, which are used for preparing dairy starter, sauerkraut, ensiling feed, and producing a blood plasma substitute. To obtain a guaranteed final result, it is necessary to strictly control the resulting quality of lactic acid bacteria.

You need an appropriate nutrient medium and a preparation with a pure culture of lactic acid bacteria grown in laboratory conditions. Next, the cultivation process is left until the third phase (equilibrium) occurs, after which the “harvest” of lactic acid bacteria can begin to be collected.

Bacterial overgrowth syndrome

The growth of bacterial cells is not always beneficial; an excessive increase in bacterial populations in the human body can be dangerous to health. Violation of the qualitative and quantitative composition of the intestinal microflora is called clinical syndrome of bacterial overgrowth. Doctors say that using the term “dysbacteriosis” to describe this process is not entirely correct. The fact is that the number of anaerobic bacteria beneficial to the body (bifidobacteria) actually decreases, but the number of opportunistic cells (for example, aerobic E. coli) increases.

Different bacteria live in different parts of the gastrointestinal tract. In the small intestine, as you progress, the composition of the microflora and the number of microorganisms gradually changes. Aerobic (growing in oxygen) species of bacteria gradually give way to anaerobic (oxygen-free environment). In clinical overgrowth syndrome, the bacterial spectrum shifts towards gram-negative (most pathogenic), facultative aerobic and anaerobic organisms.

As you approach the colon, the number of anaerobic bacteria (bifidobacteria and bacteroides) increases. The main representatives of anaerobic microflora - bifidobacteria - are responsible for the synthesis of proteins, B vitamins, various acids and other substances necessary for life. Aerobic microorganisms (Escherichia coli) produce a number of vitamins and acids that participate in digestion and support immunity.

Lactic acid bacteria are another representative of the intestinal microflora. They belong to microaerophilic organisms, i.e. one of the growth and reproduction factors of lactic acid bacteria is oxygen, but in very small quantities. These microorganisms are responsible for regulating the acidity of the gastrointestinal tract, thereby inhibiting the growth of putrefactive bacteria.

Each type of bacteria performs its own, clearly defined function. In overgrowth syndrome, fecal microflora that normally lives in the large intestine (E. coli or anaerobic cells) enters the small intestine. The quantitative and qualitative composition of the bacterial microflora changes, the performance of some functions slows down or becomes impossible. Conditions appear for the growth and reproduction of pathogenic bacteria.

Clinical criteria of the disease

Criteria for the development of bacterial overgrowth syndrome can be:

• indigestion, decreased immunity, changes in stomach acidity;
• violation of the integrity of the intestinal tract;
• consequences of surgery;
• diseases of the gastrointestinal tract;
• stress;
• uncontrolled use of antibiotic drugs.

The clinical manifestations of bacterial overgrowth syndrome are easily confused with other diseases; they often overlap each other, completely distorting the picture. A diagnosis in such cases can only be made with the help of special tests aimed at identifying overgrowth syndrome, determining not only the number, but also the species of bacteria. This approach will allow you to select the necessary medications to correct the composition of the microflora.

Clinical symptoms of the disease:

• at an early stage of the disease, diarrhea and flatulence appear;
• bloating and cramping pain;
• fatigue, weakness;
• fast weight loss.

Antibacterial drugs are used to treat overgrowth syndrome. In the future, probiotic and prebiotic preparations will be needed to restore the microflora.

A wide variety of bacterial cells (autotrophs and heterotrophs, aerobic and anaerobic, spore-forming and non-spore-forming, etc.) dictates certain conditions for their reproduction. The basic principle of cultivation on an industrial scale is strict control of environmental conditions and growth rate. In nature, ideal environments for the development of microorganisms rarely exist. Otherwise, bacteria would have long ago filled all available space.

The term "growth" means an increase in the cytoplasmic mass of an individual cell or group of bacteria as a result of the synthesis of cellular material. Having reached a certain size, the cell stops growing and begins to multiply. Reproduction refers to the ability of microorganisms to reproduce themselves, i.e. an increase in the number of individuals per unit volume. Thus, reproduction is an increase in the number of individuals in a microbial population.

Bacteria reproduce primarily by simple transverse division (vegetative propagation) in different planes. The division process begins with the formation of a transverse septum, which divides the cytoplasm of the mother cell into two daughter cells. During the division process, DNA replication occurs, thus, each daughter cell receives its hereditary information from the mother cell.

There are three types of reproduction in fungi: vegetative, asexual and sexual.

During vegetative propagation, parts of the mycelium are separated from the mycelium, which, as they develop, form a new mycelium.

Asexual reproduction is carried out using spores that mature in special sporulation organs. Mature spores are released into the environment and, given favorable conditions, germinate, giving rise to new hyphae. A type of asexual reproduction is budding. This process is typical for yeast fungi.

In sexual reproduction, sporulation is preceded by the fusion of haploid male and female gametes. As a result, a zygote appears and a diploid phase begins with a paired set of chromosomes. The sexual process in different types of mushrooms occurs differently and has its own characteristics.

DNA replication and cell division occur at a certain speed, which depends on the type of microorganism, the age of the culture, the composition of the nutrient medium, temperature, the presence or absence of oxygen and some other factors. Thus, in E. coli a new generation is formed in 15...30 minutes, in nitrifying bacteria - in 5...10 hours, and in Mycobacterium tuberculosis - in 18...24 hours. The more optimal the conditions, the faster the microbial cell divides. In the same Escherichia coli, when cultivated in peptone water, division occurs after 33 minutes, and when cultivated in meat-peptone broth, after 23 minutes. The rate of fission is also greatly influenced by the ambient temperature. Thus, in pathogenic microorganisms adapted to the body temperature of animals and humans, reproduction at a temperature of 37...39 0 C occurs several times faster than at a temperature of 18...20 0 C.

Although microorganisms multiply quickly, they are not unlimited. Under natural conditions, there are many factors that limit the growth of microbial populations. These include: depletion of the nutrient medium, unfavorable temperature, light, waste products of the microorganisms themselves, which accumulate in the nutrient medium. The process of development of a bacterial population in a permanent environment proceeds unevenly, but has its own patterns and a certain sequence. It is customary to distinguish several phases in this process. The development phases of a bacterial population differ in time and in the number of living and dying microorganisms. The development history of each individual population will vary significantly, but the sequence with which one phase replaces another remains unchanged.

I.Initial phase (stationary, latent, resting phase). It represents the period from the moment bacteria are inoculated on a nutrient medium until they begin to grow. During this phase, the number of bacteria does not increase and may even decrease.

II.Reproduction delay phase. During this period, bacterial cells grow rapidly, but reproduce weakly. The duration is about two hours and depends on a number of conditions: the age of the culture, the biological characteristics of microorganisms, the usefulness of the nutrient medium, temperature, etc.

III.Logarithmic phase. During this period, the rate of cell reproduction and increase in population size is maximum.

IV.Negative acceleration phase. Occurs due to depletion of the nutrient medium, i.e. specific nutrients necessary for the viability of a given species are running out. The rate of bacterial reproduction decreases, the number of dividing individuals decreases, and the death toll increases.

V.Stationary maximum phase. The number of new bacteria is almost equal to the number of dead ones, i.e. an equilibrium occurs between dying cells and newly formed ones.

VI.Acceleration phase of death. The number of dead cells is superior to those newly formed.

VII.Logarithmic death phase. Cell death occurs at a constant rate.

Reproduction

n Bacteria multiply binary fission, less often by budding, actinomycetes - by spores and fragmentation.

n Gram-negative bacteria divided by constriction.

n Gram-positive bacteria divide by ingrowth of synthesized division septa into the cell

After being introduced into the environment, bacteria adapt to its conditions and multiply relatively slowly (lag phase). Then comes the exponential growth phase (exponential phase). Further, the environment is depleted, toxic metabolic products accumulate in it, which is manifested by a decrease in the rate of reproduction and a cessation of the increase in the number of cells (stationary phase).

Thus, growth in a periodic culture is subject to laws that are valid not only for unicellular, but also for multicellular organisms. Subsequently, the bacterial culture may die or be significantly reduced (die-off phase). Spore-forming species enter the sporulation stage; in non-spore-forming species, the formation of anabiotic forms is possible (see below). In some cases, a growth acceleration phase (the beginning of the exponential phase) and a growth deceleration phase (the transition to the stationary phase) are additionally distinguished.

Lag phase bacterial growth corresponds to a period of physiological adaptation, including enzyme induction, synthesis and assembly of ribosomes. The duration of the phase depends mainly on the age of the inoculum of bacteria and the previous cultivation conditions. If the inoculum is taken from an old culture (in the stationary growth phase), then the bacteria need time to adapt to new conditions. If the sources of energy and carbon in the new environment differ from those available in the previous culture, then adaptation to new conditions may require the synthesis of new enzymes that were not previously needed.

Exponential phase bacterial growth (logarithmic) is characterized by the maximum rate of cell division. For a specific bacterial species under specific growth conditions, the generation time (that is, the time required for the number of bacteria to double) is constant throughout the logarithmic phase, but varies among different species and strains, and also depends on the composition of the medium and cultivation conditions. The generation time on the optimal medium can be short (for E. coli 20 minutes) or long (for Mycobacterium tuberculosais 6 hours). In this phase, the maximum accumulation of bacterial metabolites (for example, toxins, bacteriocins) occurs in the medium.

Stationary phase bacterial growth. During this period, the availability of essential nutrients becomes a limiting factor. A balance is established between cell growth and division and the process of cell death. Spore-forming bacteria (for example, the genera Bacillus and Clostridium) are able to enter the sporulation phase, which is activated when the bacteria are in conditions of limited nutrition. At a certain point, the ratio of dying, newly formed and resting cells becomes stable; such a state is known as the maximum stationary phase. The biomass of bacteria in the stationary phase is referred to as the “harvest” or “biomass yield” (the difference between the maximum and initial biomass); or “economic coefficient”, if the increase in biomass is related to a unit of growth-limiting substrate.

Dieback phase(decline, lysis) includes a period of logarithmic death, which turns into a period of decreasing rate of bacterial death. The reasons for the death of bacteria in normal nutrient media are not completely clear. It is understandable that acids accumulate in the medium (during the growth of Escherichia, Lactobacillus). Sometimes bacteria are destroyed by their own enzymes (autolysis). The rate of death varies widely depending on the living conditions and characteristics of the microorganism (for example, enterobacteriaceae die off slowly, and bacilli die off quickly).

Deep cultivation method bacteria are used in the industrial cultivation of bacterial biomass, for which special reactor boilers are used. They are equipped with systems for maintaining temperature, supplying various nutrients to the broth, mixing biomass and constantly supplying oxygen. The creation of aerobic conditions throughout the entire thickness of the medium promotes the flow of energy processes along the aerobic path, which contributes to the maximum utilization of the energy potential of glucose and, consequently, the maximum yield of biomass.

Flow media method(industrial cultivation method) allows you to constantly maintain a bacterial culture in the exponential growth phase, which is achieved by constantly adding nutrients and removing a certain number of bacterial cells. The presence of bacteria in the exponential stage of growth ensures the maximum yield of various biologically active substances (vitamins, antibiotics, etc.).

The growth of a bacterial cell should be understood as an increase in the mass of its cytoplasm, which occurs as a result of the synthesis of cellular material during nutrition. The growth of a bacterial population goes through 4 stages: 1) lag phase, 2) exponential or logarithmic phase, 3) stationary phase, 4) dying phase.

LAG PHASE (4 -5 hours) Occurs after the seed is introduced into the medium. This is the period of adaptation of bacteria to the nutrient medium, when differential activation of exo- and endoenzymes occurs for the subsequent implementation of the enzyme-substrate reaction. With stable DNA content, there is a sharp increase in bacterial protein and RNA.

LAG PHASE (4 -5 hours) The duration of the lag phase is usually short, measured in hours and depends on the type of bacteria, the multiplicity of inoculation on a given medium, the state of the culture, the temperature used for cultivation, and the composition of the nutrient medium. In the absence of visible signs of growth in the lag phase, an increase in biomass occurs, as a result of which the size of the bacterial cell increases several times.

LAG PHASE (4 -5 hours) Having reached a certain size, having “accumulated” the required amount of protein, RNA and DNA, activating exo- and endoenzymes, the bacterial cell begins to actively divide. Bacteria reproduce by transverse cell division.

LOGARITHMIC GROWTH PHASE (5 - 6 hours) This is the phase of reproduction, carried out through the binary division of the mother cell into two daughter cells. “The chain reaction of progressively accelerating binary fission of bacterial cells leads to a rapid increase in bacterial mass in the nutrient medium, intensive consumption of its energy substrate and accumulation of bacterial metabolic products.

STATIONARY GROWTH PHASE As a result, the environment becomes increasingly unfavorable for further growth and reproduction of bacteria. During the stationary phase, the rate of reproduction remains constant. Depending on the type of bacteria being cultivated, it can last for a long time, after which the fourth stage occurs -

DYING PHASE The dying phase is characterized by the progressive death of bacterial cells in a logarithmic manner. The duration of this phase ranges from 48 hours to several weeks.

The nature of bacterial growth on liquid nutrient media is different - diffuse turbidity of the nutrient medium, - formation of a film or sediment (bottom growth), - growth in the form of a “ball of cotton wool”. The growth pattern on liquid nutrient medium is used to differentiate bacteria.

Nutrient media For the cultivation of bacteria in laboratory conditions, artificial nutrient media of various compositions are used. Conventional or simple nutrient media (meat peptone agar, meat peptone broth) are used for initial crops (primary). Complex media include selective and differential diagnostic nutrient media.

Nutrient media Elective media ensure the growth of only a certain type of microorganisms, while the accompanying microflora is suppressed by special additives. Differential diagnostic nutrient media are used to study the biochemical properties of microorganisms and make it possible to differentiate bacteria by enzymatic activity.

CLASSIFICATION OF MICROORGANISMS As new species of bacteria were studied and identified, each newly created classification reflected the level of development of science. The classification of microorganisms, that is, the systematization of all known species, was based on a number of characteristics:

Sequence of determining a microorganism I. Which kingdom does it belong to - prokaryotes or eukaryotes II. Which of the main categories does it belong to: 1. Gram-negative eubacteria that have cell walls. 2. Gram-positive eubacteria with cell walls. 3. Eubacteria lacking cell walls. 4. Archaebacteria.

A total of 35 groups of microorganisms are known III. Which group within 4 categories does the microorganism belong to: 1. Spirochetes 2. Aerobic /microaerophilic, motile, spiral-shaped/, vibroid, gram-negative bacteria. 3. Non-motile gram-negative, curved bacteria. 4. Gram-negative, anaerobic, microaerophilic rods and cocci.

I. gram-negative eubacteria with a cell wall 5. Facultative anaerobic, gram-negative rods. 6. Gram-negative, anaerobic, straight, curved and spiral rods. 7. Bacteria that carry out the dissimilatory reduction of sulfate or sulfur. 8. Anaerobic gram-negative cocci. 9. Rickettsia and chlamydia.

I. gram-negative eubacteria with a cell wall 10. Anoxygenic phototrophic bacteria. 11. Oxygenic phototrophic bacteria. 12. Aerobic chemolithotrophic bacteria. 13. Budding and/or outgrowth-forming bacteria. 14. Bacteria with covers. 15. Non-photosynthetic gliding bacteria that do not form fruiting bodies. 16. Sliding bacteria forming fruiting bodies.

II. Gram-positive eubacteria with cell walls. 1. Gram-positive cocci. 2. Gram-positive rods and cocci that form endospores. 3. Gram-positive rods that do not form spores and are of regular shape. 4. Non-spore-forming gram-positive rods of irregular shape. 5. Mycobacteria. 6. Actinomycetes.

IV. Archaebacteria. 1. Methanogens. 2. Sulfate-reducing archaea. 3. Extremely halophilic archaebacteria. 4. Archaebacteria lacking a cell wall. 5. Extreme thermophiles and hyperthermophiles metabolizing S

Sequence for identifying a microorganism IV. What genus does the microorganism belong to? V. What family does the microorganism belong to? VI. What type of microorganism is it?

Construction of the taxonomic name of the microorganism. 1. KINGDOM 2. CATEGORY. 3. GROUP. 4. ROD. 5. FAMILY. 6. VIEW

Advantages of the modern classification of microorganisms The phylogenetic systematization created to date has all the advantages and disadvantages of a classification based on one characteristic. The advantages include the almost complete identity of the results obtained in various laboratories around the world. To establish species identity, they also began to additionally evaluate the degree of DNA-DNA homology using type strains.

Disadvantages of the existing classification of microorganisms. The disadvantage of the existing classification is that it does not provide an idea of ​​the functions of bacteria. Therefore, the creation of a phenotypic or functional classification is now of great importance for practical microbiologists. To quickly determine the taxonomic position of microorganisms, use the Bergey Determinant. This reference publication is constantly updated with new groups of isolates and is periodically reprinted. Now the 11th edition is current.

Formation of a modern classification of microorganisms. At the present stage, identification of the phylogenetic position of prokaryotes, including uncultivated ones, is being developed on the basis of nucleotide sequences of 16 S r RNA. Improved sequencing and data processing techniques have made this approach practically no alternative to determining the genus of new organisms. The description of new bacterial taxa has occurred at a very rapid pace in the last 50 years, thanks to advances in the study of anaerobes.

The difference between classification and identification In addition to classifications, in microbiology there are schemes for identifying isolated bacterial cultures. To build an identification scheme, select characteristics of microorganisms that are easy to determine, and for classification, often require the use of complex methods. In this case, the identification scheme should include a small number of characteristics, and for taxonomic determination, the classification uses as many characteristics as possible.

THANK YOU FOR YOUR ATTENTION. YOU HAVE LISTENED LECTURE No. 3 ON MICROBIOLOGY ON THE TOPIC: “GROWTH AND REPRODUCTION OF MICROORGANISMS. EVOLUTION AND CLASSIFICATION OF MICROORGANISMS".