Features of metabolism in bacteria:

1) the variety of substrates used;

2) intensity of metabolic processes;

4) the predominance of decay processes over synthesis processes;

5) the presence of exo- and endoenzymes of metabolism.

There are two types of metabolism in the process of metabolism:

1) plastic (constructive):

a) anabolism (with energy costs);

b) catabolism (with the release of energy);

2) energy metabolism (occurs in the respiratory mesosomes):

a) breathing

b) fermentation.

Depending on the acceptor of protons and electrons among bacteria, aerobes, facultative anaerobes and obligate anaerobes are distinguished. For aerobes, the acceptor is oxygen. Facultative anaerobes in oxygen conditions use the process of respiration, in anoxic conditions - fermentation. For obligate anaerobes, only fermentation is characteristic; under oxygen conditions, the death of the microorganism occurs due to the formation of peroxides, and cell poisoning occurs.

In the microbial cell, enzymes are biological catalysts. According to the structure, they distinguish:

1) simple enzymes (proteins);

2) complex; consist of protein (active center) and non-protein parts; required for enzyme activation.

There are also:

1) constitutive enzymes (they are constantly synthesized regardless of the presence of a substrate);

2) inducible enzymes (synthesized only in the presence of a substrate).

The set of enzymes in a cell is strictly individual for the species. The ability of a microorganism to utilize substrates through its set of enzymes determines its biochemical properties.

According to the place of action, there are:

1) exoenzymes (act outside the cell; take part in the process of disintegration of large molecules that cannot penetrate inside the bacterial cell; characteristic of gram-positive bacteria);

2) endoenzymes (act in the cell itself, provide the synthesis and breakdown of various substances).

Depending on the chemical reactions catalyzed, all enzymes are divided into six classes:

1) oxidoreductases (catalyze redox reactions between two substrates);

2) transferases (carry out intermolecular transfer of chemical groups);

3) hydrolases (perform hydrolytic cleavage of intramolecular bonds);

4) lyases (attach chemical groups two bonds, and also carry out reverse reactions);

5) isomerases (carry out isomerization processes, provide internal conversion with the formation of various isomers);

6) ligases, or synthetases (connect two molecules, resulting in the splitting of pyrophosphate bonds in the ATP molecule).

Types of plastic exchange

The main types of plastic exchange are:

1) protein;

2) carbohydrate;

3) lipid;

4) nucleic.

Protein metabolism is characterized by catabolism and anabolism. In the process of catabolism, bacteria decompose proteins under the action of proteases with the formation of peptides. Amino acids are formed from peptides by the action of peptidases.

The breakdown of proteins under aerobic conditions is called smoldering, and under anaerobic conditions, decay.

As a result of the breakdown of amino acids, the cell receives ammonium ions necessary for the formation of its own amino acids. Bacterial cells are able to synthesize all 20 amino acids. Leading among them are alanine, glutamine, asparagine. They are involved in the processes of transamination and transamination. In protein metabolism, synthesis processes predominate over decay, while energy consumption occurs.

In carbohydrate metabolism in bacteria, catabolism prevails over anabolism. Complex carbohydrates of the external environment can be broken down only by those bacteria that secrete enzymes - polysaccharidases. Polysaccharides are broken down to disaccharides, which, under the action of oligosaccharidases, decompose to monosaccharides, and only glucose can enter the cell. Part of it goes to the synthesis of its own polysaccharides in the cell, the other part undergoes further splitting, which can go in two ways: along the path of anaerobic decomposition of carbohydrates - fermentation (glycolysis) and under aerobic conditions - along the path of combustion.

Depending on the final products, the following types of fermentation are distinguished:

1) alcohol (typical for mushrooms);

2) propionic acid (typical for clostridia, propion bacteria);

3) lactic acid (typical for streptococci);

4) butyric (typical for sarcin);

5) butylene glycol (typical for bacilli).

Along with the main anaerobic breakdown (glycolysis), there may be auxiliary pathways for the breakdown of carbohydrates (pentose phosphate, ketodeoxyphosphogluconic, fructose diphosphate, etc.). They differ in key products and reactions.

Lipid metabolism is carried out with the help of enzymes - lipoproteinases, lecitinases, lipases, phospholipases.

Lipases catalyze the breakdown of neutral fatty acids, that is, they are responsible for the cleavage of these acids from glycerol. When fatty acids are broken down, the cell stores energy. The final breakdown product is the acetyl-CoA enzyme.

Lipid biosynthesis is carried out by acetyl-carrying proteins. In this case, the acetyl residue passes to glycerophosphate with the formation of phosphatidic acids, and they already enter into chemical reactions with the formation of esters with alcohols. These transformations underlie the synthesis of phospholipids.

Bacteria are able to synthesize both saturated and unsaturated fatty acids, but the synthesis of the latter is more characteristic of aerobes, since it requires oxygen.

Nucleic metabolism of bacteria is associated with genetic metabolism. The synthesis of nucleic acids is important for the process of cell division. Synthesis is carried out with the help of enzymes: restriction enzyme, DNA polymerase, ligase, DNA-dependent RNA polymerase.

Restriction enzymes cut out sections of DNA, removing unwanted inserts, and ligases provide cross-linking of nucleic acid fragments. DNA polymerases are responsible for the replication of daughter DNA along the maternal DNA. DNA-dependent RNA polymerases are responsible for transcription, building RNA on a DNA template.

The life of the human body is a very complex and unique phenomenon, however, it has such mechanisms that support its existence and at the same time they can be disassembled into the simplest components that are accessible to everyone. Here, first of all, it must be said about the metabolism of bacteria, which is only conditionally complex, in fact, such a process as the metabolism of bacteria is quite simple. The science of microbiology helps to get acquainted in detail with the process of metabolism of microorganisms. The processes being studied help shape new forms of treatment for a variety of ailments.

If we talk about big picture metabolic bacterial process, then we are talking about a certain reaction cycle, and some reactions are responsible for providing the human body with energy, and as for others, they are ways to replenish the body with matter, that is, in fact, they are a kind of building material. If we talk about the metabolism of bacterial cells, then it is impossible to find differences from biological principles of a general type. Bacteria are the basis of the supporting mechanism of the life process of living cells.

There are 2 types of such a process that depend on metabolic products:

1. Catabolism destructive type or destructive reaction. This type of metabolism can be provided by oxidative respiration. The fact is that when the respiratory process is carried out, elements of the oxidative type flow into the human body, which begin to oxidize chemical compounds of a certain type when ATP energy is released. Such energy is available in cells in the form of phosphate-type bonds.
2. Anabolism constructive type or a creative reaction. We are talking about the process of biosynthesis that organic molecules undergo, they are necessary character to keep the cell alive. The whole process takes place as reactions of a chemical type, substances and products of the intracellular type take part in such reactions. Such reactions receive energy due to the fact that the stored energy stored in ATP is consumed.

Most of the processes of the metabolic type take place in a cell of the prokaryotic type, and such a process is of a one-time nature, all this has the form of a closed-type cycle. When the metabolic process takes place, products begin to form, which are accompanied by cell-type structures, then a biosynthetic reaction begins to start, in which certain enzymes take part, they carry out the process of synthesis of an energy nature. These types of microbial metabolism are not the only ones, there are others.

The metabolism of microorganisms refers to the substrate, here we are talking about several stages:

• peripheral stage when the substrate is processed by enzymes that are produced by bacteria;
• intermediate stage when products of an intermediate type begin to be synthesized in the cell;
• final stage- it begins the process of release of final products into the environment that surrounds it.

All the features of this process are due to the fact that there are two types of enzymes (we are talking about protein-type molecules that can accelerate reactions in the cellular structure:

1. First of all, it must be said about exoenzymes, which are protein-type molecules, when the cell begins to be produced outside, and the external substrate begins the process of destruction to molecules of the original type.
2. Separately, we talk about endoenzymes, which are also protein-type molecules that act inside the cell, and then a joint reaction begins with substrate molecules that come from outside.

It should be noted that there are a number of enzymes that are produced by the cellular structure on an ongoing basis (of a constitutive nature), and there are also those that carry out production in the form of a reaction to when a certain substrate appears.

Energy type metabolism

Such a process in bacteria is carried out in certain ways of a biological type:

1. The first way is chemotrophic, when energy is obtained in the course of chemical reactions.
2. The second way is phototrophic (here we are talking about the energy of photosynthesis).

If we talk about how bacteria breathe in a chemotrophic way, then there can be 3 ways:

• oxygen character oxidation;
• oxidation without the use of oxygen;
• fermentation process.

Features of bacterial metabolism

• Such processes are characterized by extreme speed and intensity. Within just one day, one bacterium is able to process such an amount of nutrients that exceeds its own weight by 40 times!
• To all external conditions, even the most unfavorable bacteria adapt very quickly.
• As for the nutritional process, it occurs through the entire cell surface. It is noteworthy that prokaryotes are not able to swallow nutrients, inside cell structure they are not able to be digested, their splitting is carried out outside the cell, and chemosynthesis of cyanobacteria is also observed.

How do microorganisms grow and reproduce?

It should be noted that growth is the process when an individual increases in size, and as for the reproduction process itself, this is when the population begins to increase.

It is noteworthy that bacteria are able to multiply in such a way that binary fission is simply carried out, however, this method is far from the only one, there is also budding. If the bacteria have a gram-positive form, then there is a formation of a partition from a cell-type wall and a cytoplasmic-type membrane, which is capable of growing inward. If the bacteria are gram-negative, then a constriction begins to form, after which the cell splits into a couple of individuals.

The speed of the breeding process is noteworthy, it can be different. If we talk about the vast majority of bacteria, then they divide every half hour. And there are tuberculosis mycobacteria, the process of division of which is slower, suffice it to say that for one division it may take at least 18 hours. Spirochetes also do not divide quickly, about 10 hours, so you can see how the metabolism of microorganisms differs.

If bacteria are seeded in liquid culture medium, while taking a certain volume, and then take a sample every hour, then the bacterial growth has the shape of a curved line.

Such substances grow in several phases:

• the latent phase, in which bacteria have the ability to quickly adapt to the nutritional environment, and as for their number, it does not increase;
• a logarithmic growth phase, when the bacterial count begins to increase exponentially;
• the growth phase of a stationary type, when as many new substances appear as they die, and living microorganisms remain constant, all this can reach a maximum level. A term such as M-concentration is used here, this is a value that is characteristic of all bacterial types;
• the dying phase is a process in which the number of dead cells becomes greater than the number of viable cells. This happens because metabolic products accumulate in the body and the environment is depleted.

In conclusion, it should be noted that the metabolism of all bacteria and microbes may have certain differences; a variety of factors may take place here. Of great importance are the individual characteristics of the human body. As for such a process as the regulation of metabolism, it began to be studied even in prokaryotes, and specifically in prokaryotes (these are the intestinal coli operons).

To date, there are a variety of research methods. If sulfur bacteria are studied, then the study has its own characteristics, and other methods can be used to study bacterial changes. And iron bacteria deserve special attention, which have a unique feature of oxidizing ferrous iron.

annotation

Introduction

1. General concepts of metabolism and energy

2. Constructive metabolism

3.1 Carbon sources

4. Types of metabolism of microorganisms

7. Energy metabolism of chemoorganotrophs using the process of respiration

8. Energy metabolism of chemolithoautotrophs

Conclusion

This course work contains basic information about the constructive and energy metabolism of bacteria. The work is done on 37 sheets. Contains 5 figures and 1 table.

The totality of the processes of transformation of matter in a living organism, accompanied by its constant renewal, is called metabolism or metabolism.

The most important properties of living organisms are the ability to self-reproduce and their closest relationship with the environment. Any organism can exist only under the condition of a constant influx of nutrients from the external environment and the release of waste products into it.

Nutrients absorbed by the cell as a result of complex bio chemical reactions converted into specific cellular components. The totality of biochemical processes of absorption, assimilation of nutrients and the creation of structural elements of the cell due to them is called constructive metabolism or anabolism. Constructive processes go with the absorption of energy. The energy needed for the biosynthetic processes of other cellular functions, such as movement, osmoregulation, etc., the cell receives due to the flow of oxidative reactions, the totality of which is energy metabolism, or catabolism (Fig. 1).

All living organisms can only use chemically bound energy. Every substance has a certain amount of potential energy. Its main material carriers are chemical bonds, the breaking or transformation of which leads to the release of energy.

Energy level chemical bonds unequal. For some, it has a value of the order of 8-10 kJ. Such connections are called normal. Other bonds contain much more energy - 25-40 kJ. These are the so-called macroergic bonds. Almost all known compounds with such bonds include phosphorus and sulfur atoms involved in the formation of these bonds.

Adenosine triphosphate (ATP) plays an important role in cell life. Its molecule consists of adenine, ribose and three phosphoric acid residues: (Appendices Fig 2)

ATP occupies a central place in the energy metabolism of the cell. Macroergic bonds in the ATP molecule are very fragile. Hydrolysis of these bonds leads to the release of a significant amount of free energy:

ATP + H20 → ADP + H3P04 - 30.56 kJ

Hydrolysis proceeds with the participation of specific enzymes, providing energy for biochemical processes that take place with the absorption of energy. In this case, ATP plays the role of an energy supplier. Having a small size, the ATP molecule diffuses into various parts of the cell. The supply of ATP in cells is continuously renewed due to reactions of addition of a phosphoric acid residue to an adenosine diphosphoric acid (ADP) molecule:

ADP + H3P04 → ATP + H20

The synthesis of ATP, like hydrolysis, occurs with the participation of enzymes but is accompanied by the absorption of energy, the methods of obtaining which in microorganisms, although diverse, can be reduced to two types:

1) use of light energy;

2) use of the energy of chemical reactions.

In this case, both types of energy are transformed into the energy of chemical bonds of ATP. Thus, ATP acts as a transformer in the cell.

Anabolism and catabolism are inextricably linked, making up a single whole, since the products of energy metabolism (ATP and some low molecular weight compounds) are directly used in the constructive metabolism of the cell (Fig. 6.1).

In the cells of microorganisms, the ratio between energy and constructive processes depends on a number of specific conditions, in particular, on the nature of nutrients. Nevertheless, catabolic reactions usually outnumber biosynthetic processes in volume. The interrelation and conjugation of these two types of metabolism is manifested primarily in the fact that the total volume of constructive processes depends entirely on the amount of available energy obtained in the course of energy metabolism.

Constructive metabolism is aimed at the synthesis of four main types of biopolymers: proteins, nucleic acids, polysaccharides and lipids.

Below is a generalized conditional scheme for the biosynthesis of complex organic compounds, where the following main stages are distinguished: formation from protozoa inorganic substances organic precursors (I), from which “building blocks” (II) are synthesized at the next stage. In the future, the building blocks, binding to each other by covalent bonds, form biopolymers (III): Applications (Fig. No. 3)

The presented scheme of biosynthetic processes does not reflect the complexity of the transformation of low molecular weight precursors into high molecular weight building blocks. In fact, the synthesis proceeds as a series of successive reactions with the formation of various metabolic intermediates. In addition, the levels of development of the biosynthetic abilities of microorganisms are very different. In some microbes, constructive metabolism includes all the stages shown in the diagram, in others it is limited to the second and third or only the third stage. That is why microorganisms differ sharply from each other in their nutritional needs. However, the elemental composition of food is the same for all living organisms and must include all the components that make up the cellular substance: carbon, nitrogen, hydrogen, oxygen, etc.

Depending on the carbon sources used in constructive metabolism, microorganisms are divided into two groups: autotrophs and heterotrophs.

Autotrophs (from the Greek "autos" - itself, "trophe" - food) use carbon dioxide as the only source of carbon and synthesize all the necessary biopolymers from this simple inorganic precursor compound. Autotrophs have the highest biosynthetic capacity.

Heterotrophs (from the Greek "heteros" - another) need organic sources of carbon. Their nutritional requirements are extremely varied. Some of them feed on the waste products of other organisms or use dead plant and animal tissues. Such microorganisms are called saprophytes (from the Greek "sapros" - rotten and "phyton" - plant). The number of organic compounds used by them as carbon sources is extremely large - these are carbohydrates, alcohols, organic acids, amino acids, etc. Almost any natural compound can be used by one or another type of microorganism as a source of nutrition or energy.

Nitrogen is required for the synthesis of cellular proteins. In relation to the sources of nitrogen nutrition among microorganisms, autoaminotrophs and heteroaminotrophs can be distinguished. The former are able to use inorganic nitrogen (ammonium, nitrate, molecular) or the simplest forms of organic (urea) and build various proteins of their body from these compounds. In this case, all forms of nitrogen are first converted to the ammonium form. This most reduced form of nitrogen easily transforms into an amino group. Heteroaminotrophs need organic forms of nitrogen - proteins and amino acids. Some of them require a complete set of amino acids, others create the necessary protein compounds from one or two amino acids by converting them.

Many microorganisms that are heterotrophic with respect to carbon are autoaminotrophs. These include bacteria involved in wastewater treatment.

Microorganisms satisfy the need for oxygen and hydrogen for constructive exchange at the expense of water and organic nutrients. The sources of ash elements (P, S, K, Mg, Fe) are the corresponding mineral salts. The need for these elements is small, but the presence in the environment is mandatory. In addition, for the normal functioning of microbes, microelements are necessary - Zn, Co, Cu, Ni, etc. Some of them are part of natural nutrition microbes, part is absorbed by them from mineral salts.

The methods of obtaining food, i.e., the methods of nutrition of microorganisms, are very diverse. There are three main types of nutrition: holophyte, saprozoic, holozoic.

Holophyte nutrition (from the Greek "holo" - whole, "fit" - a plant) is carried out according to the type of plant photosynthesis. Such nutrition is inherent only to autotrophs. Among microorganisms, this method is characteristic of algae, colored forms of flagellates and some bacteria.

Heterotrophic microorganisms feed either on solid food particles or absorb dissolved organic matter.

Holozoic nutrition predetermines the development in microorganisms of special organelles for digesting food, and in some - for its capture. For example, uncolored flagella and ciliary ciliates have a mouth opening to which food is driven, respectively, by flagella or cilia. The most highly organized ciliates form a flow of water in the form of a funnel with their perioral cilia, directed by the narrow end into the mouth. Food particles are deposited at the bottom of the funnel and swallowed by ciliates. Such ciliates are called sedimentators. Amoebas feed by phagocytosis.

Microorganisms with a holozoic mode of nutrition for constructive metabolism mainly use the cytoplasm of other organisms - bacteria, algae, etc. and have special organelles for digestion. The digestive process in protozoa is carried out in digestive vacuoles.

Digestion consists in the hydrolytic breakdown of complex organic substances into simpler compounds. In this case, carbohydrates are hydrolyzed to simple sugars, proteins to amino acids, and glycerol and higher fatty acids are formed during the hydrolysis of lipids. The products of digestion are absorbed into the cytoplasm and undergo further transformation.

Bacteria, microscopic fungi, yeast do not have special organelles for capturing food, and it enters the cell through the entire surface. This way of eating is called saprozoic.

To enter the cell, nutrients must be in a dissolved state and have the appropriate molecular size. For many macromolecular compounds, the cytoplasmic membrane is impermeable, and some of them cannot even penetrate the cell membrane. However, this does not mean that macromolecular compounds are not used by microorganisms as nutrients. Microorganisms synthesize extracellular digestive enzymes that hydrolyze complex compounds. Thus, the process of digestion, which occurs in vacuoles in protozoa, is carried out outside the cell in bacteria (Appendices, Fig. 4).

The size of the molecules is not the only factor that determines the penetration of nutrients into the cell.

The cytoplasmic membrane is able to pass some compounds and retain others.

There are several known mechanisms for the transfer of substances across the cell membrane: simple diffusion, facilitated diffusion, and active transfer (Appendices, Fig. 5).

Simple diffusion is the penetration of molecules of a substance into a cell without the help of any carriers.

In the saturation of the cell with nutrients, simple diffusion of great importance does not have. However, this is the way water molecules enter the cell. Quite a few important role this process is played by osmosis - the diffusion of solvent molecules through a semi-permeable membrane in the direction of a more concentrated solution.

The role of a semi-permeable membrane in the cell is performed by the cytoplasmic membrane. A huge number of molecules of various substances are dissolved in the cell sap, therefore the cells of microorganisms have a rather high osmotic pressure. Its value in many microbes reaches 0.5-0.8 MPa. In the environment, the osmotic pressure is usually lower. This causes an influx of water into the cell and creates a certain tension in it called turgor.

With facilitated diffusion, solutes enter the cell with the participation of special carrier enzymes called permeases. They, as it were, capture the molecules of dissolved substances and transfer them to the inner surface of the membrane.

Simple and facilitated diffusion are variants of passive transport of substances. The driving force for the transfer of substances into the cell in this case is the concentration gradient on both sides of the membrane. However, most substances enter the cell against a concentration gradient. In this case, energy is expended on such a transfer and the transfer is called active. Active transfer proceeds with the participation of specific proteins, is associated with the energy metabolism of the cell and allows the accumulation of nutrients in the cell at a concentration many times greater than their concentration in the cell. external environment. Active transfer is the main mechanism for the entry of nutrients into cells with saprozoic nutrition.

3. Nutrient requirements of prokaryotes

The monomers necessary for the construction of the main cellular components can be synthesized by the cell or come in finished form from the environment. The more ready-made compounds the organism must receive from the outside, the lower the level of its biosynthetic abilities, since the chemical organization of all free-living forms is the same.

3.1 Carbon sources

In constructive metabolism, the main role belongs to carbon, since all the compounds from which living organisms are built are carbon compounds. About a million of them are known. Prokaryotes are able to act on any known carbon compound, i.e., use it in their metabolism. Depending on the source of carbon for constructive metabolism, all prokaryotes are divided into two groups: autotrophs, which include organisms capable of synthesizing all cell components from carbon dioxide, and heterotrophs, whose carbon source for constructive metabolism is organic compounds. The concepts of "auto-" and "heterotrophy" thus characterize the type of constructive metabolism. If autotrophy is a rather clear and narrow concept, then heterotrophy is a very broad concept and unites organisms that differ sharply in their nutrient needs.

The next large group of prokaryotes are the so-called saprophytes - heterotrophic organisms that do not directly depend on other organisms, but need ready-made organic compounds. They use the waste products of other organisms or decaying plant and animal tissues. Most bacteria are saprophytes. The degree of exactingness to the substrate in saprophytes is very different. This group includes organisms that can only grow on fairly complex substrates (milk, animal corpses, rotting plant residues), i.e. they need carbohydrates, organic forms of nitrogen in the form of a set of amino acids, peptides, proteins, all or part of the vitamins, nucleotides or ready-made components necessary for the synthesis of the latter (nitrogenous bases, five-carbon sugars). To satisfy the need of these heterotrophs for nutrients, they are usually cultivated on media containing meat hydrolysates, yeast autolysates, plant extracts, and whey.

There are prokaryotes that require a very limited number of ready-made organic compounds for growth, mainly from among vitamins and amino acids that they are not able to synthesize themselves, and finally, heterotrophs that need only one organic source of carbon. It can be any sugar, alcohol, acid or other carbon-containing compound. Bacteria from the genus Pseudomonas are described that can use any of 200 different organic compounds as the only source of carbon and energy, and bacteria for which a narrow range of rather exotic organic substances can serve as a source of carbon and energy. For example, Bacillus fastidiosus can only use uric acid and its degradation products, and some members of the genus Clostridium grow only in a medium containing purines. They cannot use other organic substrates for growth. The biosynthetic abilities of these organisms are developed to such an extent that they themselves can synthesize all the carbon compounds they need.

A special group of heterotrophic prokaryotes living in water bodies are oligotrophic bacteria capable of growing at low concentrations in organic matter. Organisms that prefer high concentrations of nutrients are referred to as copiotrophs. If in typical copiotrophs optimal conditions for growth are created when the nutrient content in the medium is approximately 10 g / l, then for oligotrophic organisms - within 1-15 mg of carbon / l. In environments with a higher content of organic matter, such bacteria, as a rule, cannot grow and die.

Nitrogen is one of the four essential elements involved in building cells. It contains approximately 10% on a dry matter basis. Natural nitrogen occurs in oxidized, reduced and molecular forms. The vast majority of prokaryotes assimilate nitrogen in a reduced form. These are ammonium salts, urea, organic compounds (amino acids or peptides). Oxidized forms of nitrogen, mainly nitrates, can also be consumed by many prokaryotes. Since nitrogen is used in constructive cellular metabolism in the form of ammonia, nitrates must be reduced before being incorporated into organic compounds.

The reduction of nitrates to ammonia is carried out through the sequential action of two enzymes - nitrate and nitrite reductase.

The ability of individual representatives of the prokaryotic world to use the molecular nitrogen of the atmosphere was discovered long ago. IN Lately it has been shown that many prokaryotes belonging to different groups have this property: eu- and archaebacteria, aerobes and anaerobes, phototrophs and chemotrophs, free-living and symbiotic forms. The fixation of molecular nitrogen also leads to its reduction to ammonia.

3.3 Requirements for sulfur and phosphorus sources

Sulfur is a part of amino acids (cysteine, methionine), vitamins and cofactors (biotin, lipoic acid, coenzyme A, etc.), and phosphorus is an essential component of nucleic acids, phospholipids, coenzymes. In nature, sulfur is in the form of inorganic salts, mainly sulfates, in the form of molecular sulfur, or is part of organic compounds. Most prokaryotes for biosynthetic purposes consume sulfur in the form of sulfate, which is then reduced to the level of sulfide. However, some groups of prokaryotes are not capable of sulfate reduction and require reduced sulfur compounds. The main form of phosphorus in nature is phosphates, which satisfy the needs of prokaryotes in this element.

3.4 The need for metal ions

All prokaryotes require metals that can be used in the form of inorganic salt cations. Some of them (magnesium, calcium, potassium, iron) are needed in fairly high concentrations, the need for others (zinc, manganese, sodium, molybdenum, copper, vanadium, nickel, cobalt) is small. The role of the metals listed above is determined by the fact that they are part of the main cellular metabolites and, thus, participate in the implementation of the vital functions of the body.

3.5 Need for growth factors

Some prokaryotes find a need for one of the organic compounds from the group of vitamins, amino acids or nitrogenous bases, which for some reason they cannot synthesize from the carbon source used. These organic compounds, needed in very small quantities, are called growth factors. Organisms that require one or more growth factors in addition to the main carbon source are called auxotrophs, in contrast to prototrophs, which synthesize all the necessary organic compounds from the main carbon source.

For complete characteristics microorganisms use the concept of the type of metabolism. Differences in the types of metabolism of certain groups of microorganisms are due to the peculiarities of the constructive and specific energy exchanges. Depending on the energy source used to produce ATP, microorganisms are divided into phototrophs (use the energy of light) and chemotrophs (use the energy of chemical reactions).

The process of ATP formation is called phosphorylation; it is carried out in mitochondria (in eukaryotes) and enzyme systems localized on the cytoplasmic membrane (in prokaryotes). The mechanism of formation, ATP in different groups of microorganisms is not the same. There are substrate, oxidative and photophosphorylation. Any type of phosphorylation is necessarily associated with the transfer of electrons in the course of redox reactions of energy metabolism. At the same time, some microorganisms use inorganic compounds as electron (hydrogen) donors, while others use organic compounds. Accordingly, the former are called lithotrophs, the latter - organotrophs.

Thus, taking into account the type of nutrition (auto- or heterotrophic), the nature of the electron donor, the energy source (light or chemical reaction), possible combinations of constructive and energy exchanges can be represented as the following scheme.

Each of the options presented characterizes a certain type of metabolism. In table. 1 shows representatives of microorganisms of each type of metabolism

Most of the microorganisms living in natural waste waters and playing an important role in the formation of water quality and its purification belong to the eighth and first types of metabolism. In this regard, in the further presentation of the material, the main attention is paid to them.

Scheme 1. Variants of constructive and energy exchanges.

5. Energy metabolism of phototrophs

All listed in the table. 1 photosynthetic microorganisms are adapted to the use of visible light (wavelength 400-700 nm) and near infrared (700-1100 nm). This ability to exist due to the energy of light is due to the presence in the cells of organelles with specific light-sensitive pigments. Each type of microorganism has a characteristic and constant set of pigments.

Table 1

type of metabolism	Representatives
1) Photolithoautotrophy	Algae, cyanobacteria, most purple bacteria and green sulfur bacteria.
2) Photolithoheterotrophy	Partially cyanobacteria purple and green sulfur bacteria
3) Photoorganoautotrophy	Some purple bacteria
4) Photoorganoheterotrophy	Most non-sulfur purple bacteria
5) Chemolitoautotrophy	Nitrifying, thionic, some iron batteries.
6) Chemolithoheterotrophy	Colorless sulfur bacteria
7) Chemoorganoautotrophy	Some bacteria that oxidize formic acid
8) Chemoorganoheterotrophy	Protozoa, fungi, most bacteria.

For some representatives of the group of cyanobacteria, along with photolithoautotrophy, the ability to photolitho- or chemoorganoheterotrophy has been shown. A number of chemolithoautotrophic species of Thiobacillus exist by using organic compounds as sources of energy and carbon, i.e., chemoorganoheterotrophically.

Some prokaryotes can exist only on the basis of some one mode of nutrition. For example, the unicellular cyanobacterium Synechococcus elongatus can use only light as an energy source, and carbon dioxide as the main source of carbon in constructive metabolism. Characterizing the mode of existence (lifestyle, type of metabolism) of this organism, we say that it is an obligate photolithoautotroph. Many bacteria belonging to the genus Thiobacillus are obligate chemolithoautotrophs, i.e., the energy source for them is the oxidation of various sulfur compounds, and the carbon source for building body substances is carbon dioxide. The overwhelming majority of bacteria are obligate chemoorganoheterotrophs, using organic compounds as a source of carbon and energy.

Light energy is captured by a system of absorbing pigments and transferred to the reaction center, which excites chlorophyll molecules. In the dark, the chlorophyll molecule is in a stable unexcited state, when light falls on this molecule, it is excited and one of the electrons to a higher energy level. Chlorophyll molecules are closely related to the electron transport system. Each quantum of absorbed light ensures the detachment of one electron from the chlorophyll molecule, which, passing through the electron transport chain, gives its energy to the ADP-ATP system, as a result of which the light energy is transformed into the energy of the macroergic bond of the ATP molecule. This way of producing ATP is called photosynthetic phosphorylation.

However, for the implementation of biosynthetic processes of productive exchange, microorganisms, in addition to energy, need a reducing agent - a donor of hydrogen (electrons). For algae and cyanobacteria, water serves as such an exogenous hydrogen donor. The reduction of carbon dioxide in the process of photosynthesis and its transformation into the structural components of the cell in these types of microorganisms proceeds similarly to the photosynthesis of higher plants:

CO2+H2O→(CH2O)+O2

The formula CH2O symbolizes the formation of an organic compound, in which the level of carbon oxidation approximately corresponds to the carbon oxidation in the organic substances of the cell.

In photosynthetic bacteria, hydrogen donors for synthesis reactions can be both inorganic and organic substances. Most purple and green sulfur bacteria belonging to the group of photolithoautotrophs reduce CO2 using H2S as a hydrogen donor:

CO2+2H2S→(CH2O)+H2O+2S

This type of photosynthesis is called photoreduction. The main difference between bacterial photoreduction and photosynthesis of green plants and algae is that other compounds, rather than water, serve as a hydrogen donor, and photoreduction is not accompanied by oxygen release.

Unlike inorganic reducing agents, which act only as hydrogen donors, exogenous organic reducing agents can simultaneously serve as carbon sources (photoorganoheterotrophy).

The ability to use organic compounds to one degree or another is inherent in all photosynthetic bacteria. For photolithoheterotrophs, they serve only as sources of carbon nutrition, for photoorganoautotrophs they serve only as hydrogen donors. For example, non-sulfur purple bacteria of the genus Rhodopseudomonas sp. can carry out photosynthesis using isopropanol as a hydrogen donor, while reducing carbon dioxide and producing acetone:

ATP energy

CO2 + 2CH3CHOHCH3 → (CH2O) + 2CH3COCH3 + H2O

6. Energy metabolism of chemotrophs using fermentation processes

Of the three pathways for ATP formation, substrate phosphorylation is the simplest. This type of energy metabolism is characteristic of many bacteria and yeasts that carry out various types of fermentation.

Fermentation takes place under anaerobic conditions and can be defined as the process of biological oxidation of complex organic substrates for energy production, in which the final hydrogen acceptor (also organic matter) is formed during the decay of the original substrate. In this case, some organic substances serve as hydrogen donors and are oxidized, while others serve as hydrogen acceptors and, as a result, are reduced. The transfer of hydrogen from donors to acceptors is carried out with the help of redox enzymes.

In addition to carbohydrates, many bacteria are able to ferment a wide variety of compounds: organic acids, amino acids, purines, etc. The condition that determines the ability of a substance to ferment is the presence of incompletely oxidized (reduced) carbon atoms in its structure. Only in this case is intra- and intermolecular rearrangement of the substrate possible due to the conjugation of oxidative and reduction reactions without the participation of oxygen.

As a result of fermentation processes, substances accumulate in the medium in which the degree of carbon oxidation can be either higher or lower than in the original substrate. However, a strict balance of oxidative and reduction processes during fermentation leads to the fact that the average degree of carbon oxidation remains the same as that of the substrate.

There are several types of fermentations, named after the final product: alcoholic (performed by yeast and some types of bacteria), propionic (propionic bacteria), methane (methane-producing bacteria), butyric (butyric bacteria), etc.

Many microorganisms that carry out fermentation processes are obligate anaerobes, unable to develop in the presence of oxygen and even weaker oxidizing agents. Others - facultative anaerobes - can grow both in an oxygen environment and in an anoxic one. This distinctive property of facultative anaerobes is explained by the fact that they can change the mode of ATP formation, switch from oxidative phosphorylation in the presence of oxygen in the environment to its substrate absence. A characteristic feature of biological oxidation processes is their multi-stage nature. providing a gradual release of free energy contained in complex organic substrates.

Multi-stage energy metabolism is fundamentally necessary for the life of any organism. If the oxidation of complex substances in a cell proceeded in one stage, then the simultaneous release of several hundred kilojoules would lead to the release of a large amount of heat, a sharp increase in temperature and cell death, since the efficiency of energy use is limited by the capabilities of the ADP-ATP system.

The simplest example of anaerobic oxidation of glucose is lactic acid fermentation. It is caused by lactic acid bacteria, facultative anaerobes that do not form spores. The transformation of PVC during lactic acid fermentation proceeds as follows:

CH3COCOOH + OVER*H2, - CH3CHOHCOOH + OVER

Much more complicated is the mechanism of propionic acid fermentation, which serves as an energy source for a group of propionic bacteria, facultative anaerobes, immobile non-spore-forming bacteria of the genus Propionibacterium. These bacteria synthesize the final acceptor by attaching CO2 to the PVCL molecule. The process is known as heterotrophic CO2 assimilation. As a result, oxaloacetic acid is formed - a hydrogen acceptor for NAD*H2. Further enzymatic reactions lead to the formation of propionic acid.

Butyric fermentation is carried out by bacteria of the genus Clostridium. Thus, the energy yield of the fermentation process is low, since organic substances are not completely oxidized and part of the energy of the original substrate is stored in rather complex fermentation products. In most cases, during the fermentation of glucose, the cell stores two ATP molecules per 1 mol of glucose.

To obtain the energy necessary for the synthesis of cellular matter and other vital functions, microorganisms that carry out fermentation processes have to process a large amount of organic substances.

It is for these reasons that at sewage treatment plants anaerobic fermentation processes are used to treat concentrated substrates - sewage sludge.

Majority heterotrophic organisms receive energy in the process of respiration - the biological oxidation of complex organic substrates that are hydrogen donors. Hydrogen from the oxidized substance enters the respiratory chain of enzymes. Respiration is called aerobic if the role of the final acceptor of hydrogen is performed by free oxygen. Microorganisms that can only exist in the presence of oxygen are called obligate aerobes.

As energy sources - hydrogen donors - chemoorganoheterotrophs in the process of respiration can use a variety of oxidizable organic compounds: carbohydrates, fats, proteins, alcohols, organic acids, etc. In total, the respiration process during the oxidation of carbohydrates is expressed by the following equation:

С6Н12О6 + 6О → 6СО2 + 6Н2О + 2820 kJ

The initial stage of carbohydrate conversion up to the formation of PVC is completely identical to the enzymatic reactions of carbohydrate oxidation during fermentation.

In aerobic cells, PVC can be completely oxidized as a result of a series of successive reactions. The combination of these transformations constitutes a cycle called the Krebs cycle or the cycle of di- and tricarboxylic acids (CTC).

Hydrogen taken away by dehydrogenases in the cycle is transferred to the respiratory chain of enzymes, which in aerobes, in addition to NAD, includes FAD, the cytochrome system, and the final hydrogen acceptor, oxygen. The transfer of hydrogen along this chain is accompanied by the formation of ATP.

The first stage of phosphorylation is associated with the transfer of hydrogen from primary dehydrogenase to FAD. The second phosphorylation occurs when an electron passes from cytochrome b to cytochrome, the third - when an electron is transferred to oxygen. Thus, for every two hydrogen atoms (electrons) that enter the respiratory chain, three ATP molecules are synthesized. The formation of ATP simultaneously with the process of proton and electron transfer along the respiratory chain of enzymes is called oxidative phosphorylation. In some cases, the electron is included in the respiratory chain at the level of FAD or even cytochromes. At the same time, the number of synthesized ATP molecules decreases accordingly.

The total energy result of the oxidation process of 1 mole of glucose is 38 ATP molecules, of which 24 - during the oxidation of PVC in the Krebs cycle with the transfer of hydrogen to the respiratory chain of enzymes. Thus, the main amount of energy is stored at this stage. It is remarkable that the Krebs cycle is universal, i.e. characteristic of protozoa, bacteria, and cells of higher animals and plants.

Intermediates of the cycle are partly used for the synthesis of cellular substance.

Oxidation of nutrients is not always complete. Some aerobes partially oxidize organic compounds, while intermediate oxidation products accumulate in the medium.

Some microorganisms in the process of respiration do not use oxygen as the final hydrogen acceptor, but oxidized nitrogen compounds (nitrites, nitrates), chlorine (chlorates and perchlorates), sulfur (sulfates, sulfite thiosulfate), carbon (CO2), chromium (chromates and bichromates). This type of respiration is called anaerobic.

Microorganisms that carry out the process of respiration due to oxidized compounds of nitrogen and chlorine are facultative anaerobes. They have two enzymatic systems that allow them to switch from aerobic to anaerobic respiration and vice versa, depending on the presence of one or another final acceptor in the environment.

If nitrates and molecular oxygen are simultaneously present in the medium, then an acceptor will be used first of all, which makes it possible to obtain large quantity energy. Aerobic respiration accompanies three phosphorylations, anaerobic - two. However, if the concentration of oxygen in the environment is low, and the concentration of nitrates is much higher than it, microorganisms use nitrates. The decisive condition in this case is the free energy of the acceptor reduction reaction, which depends on its concentration. Anaerobic respiration using nitrates is called denitrification.

Oxidized compounds of sulfur, chromium, carbon play the role of final acceptors for different types microorganisms belonging to obligate anaerobes.

In sulfate-reducing microorganisms, an electron transport chain has been found that includes several enzymes, but the sequence of their action remains unclear.

When sulfates are used as the final hydrogen acceptor, microorganisms reduce them to sulfides:

(organic matter - hydrogen donor) + SO4→H2S + 4H2O

Anaerobic respiration using carbon dioxide is accompanied by the formation of methane.

Oxidation of reduced mineral compounds of nitrogen, sulfur, and iron serves as a source of energy for chemolithotrophic microorganisms. The division of chemolithotrophic microorganisms into groups is based on the specificity of each group with respect to the oxidizable compound. There are nitrifying bacteria, iron bacteria, bacteria that oxidize sulfur compounds.

Nitrifying bacteria oxidize ammonium nitrogen to nitrates. The process is called nitrification and goes in two phases, each of which is responsible for its own pathogens:

NH4+2O2→NO2+2H2O+557kJ/mol (1)

2NO2+O2→2NO3+146 kJ/mol (2)

The oxidation of ammonia to nitrite with the transfer of electrons to the respiratory chain serves as an energy process for a group of nitrosobacteria. Oxidation of ammonium nitrogen is a multi-stage process in which hydroxylamine (NH2OH) and hyponitrite (NOH) are formed as intermediate products. The energy substrate oxidized in the respiratory chain is hydroxylamine.

Iron bacteria (chemolithoautotrophs) do not represent a single taxonomic unit. This term combines microorganisms that oxidize reduced iron compounds to obtain energy:

4FeCO3 + O2 + 6H2O→4Fe(OH)3 + 4CO2+ 167 kJ/mol (6.9)

Quinones and cytochromes take part in the transport of electrons from ferrous iron to oxygen. Electron transfer is associated with phosphorylation.

The efficiency of energy use in these bacteria is so low that for the synthesis of 1 g of cellular substance they have to oxidize about 500 g of iron carbonate.

Bacteria that oxidize sulfur compounds and are capable of autotrophic CO2 assimilation belong to the group of thionic bacteria. Energy for the constructive metabolism of thionic bacteria is obtained as a result of the oxidation of sulfides, molecular sulfur, thiosulfates and sulfites to sulfates:

S2-+2O2→SO4+794 kJ/mol (6.10)

S0+H2O+1.5O2→H2SO4+ 585 kJ/mol (6.11)

S2O3+H2O+2O2→2SO4+2H+936 kJ/mol (6.12)

SO3 + 0.5O2→SO4 +251 kJ/mol (6.13)

The respiratory chain of thionic bacteria contains flavoproteins, ubiquinones, cytochromes.

The mechanism of CO2 assimilation for constructive purposes in all chemolithoautotrophs is similar to that in photosynthetic autotrophs using water as a hydrogen donor. The main difference is that no oxygen is released during chemosynthesis.

Thus, constructive and energy processes take place in the cell simultaneously. In most prokaryotes, they are closely related. The metabolism of prokaryotes, both energetic and constructive, is extremely diverse, which is the result of the ability of these life forms to use the widest range of organic and inorganic compounds as energy sources and initial substrates for building body substances.

Energy metabolism as a whole is associated with biosynthetic and other energy-dependent processes occurring in the cell, for the course of which it supplies energy, a reducing agent, and the necessary intermediate metabolites. The conjugation of the two types of cellular metabolism does not preclude some change in their relative scales depending on specific conditions.

The energy processes of prokaryotes in terms of their volume (scale) significantly exceed biosynthetic processes, and their course leads to significant changes in the environment. Diverse and unusual in this regard are the possibilities of prokaryotes, the ways of their energy existence. All this taken together has focused the attention of researchers primarily on the study of the energy metabolism of prokaryotes.

1. Bakulov I. A. "Energy metabolism of prokaryotes" / Veterinary /, 2006 No. 1 p 38.

2. Bailey, J. E, Ollis, David F Fundamentals of biochemical engineering. M.1989.

3. Vorobyov A.A. et al. Microbiology. M.: Medicine. 1994.

4. Gusev M.V., Mineeva L.A. Microbiology: Textbook. M.: Publishing House of Moscow State University, 1992.

5. Emelianenko P.A. et al. Veterinary microbiology. M.: Kolos. 1982.

6. Koleshko O.I. Microbiology. M.: graduate School. 1982.

7. Mishustin E.N., Emtsev V.T. Microbiology. M.: Kolos.1978.

8. Radchuk N.A. Veterinary microbiology and immunology. Moscow: Agropromizdat. 1991

9. N. A. Sudakov “Metabolism and energy” / Veterinarian / 2003 No. 5 p26.

10. V. N. Syurin “Constructive metabolism of bacteria” / Practitioner / 2005 No. 4 p. 12.

11. Schlegel G. General microbiology. M.: Mir.1987.

Microbiology: lecture notes Tkachenko Ksenia Viktorovna

3. Metabolism of a bacterial cell

Features of metabolism in bacteria:

1) the variety of substrates used;

2) intensity of metabolic processes;

4) the predominance of decay processes over synthesis processes;

5) the presence of exo- and endoenzymes of metabolism.

There are two types of metabolism in the process of metabolism:

1) plastic (constructive):

a) anabolism (with energy costs);

b) catabolism (with the release of energy);

2) energy metabolism (occurs in the respiratory mesosomes):

a) breathing

b) fermentation.

Depending on the acceptor of protons and electrons among bacteria, aerobes, facultative anaerobes and obligate anaerobes are distinguished. For aerobes, the acceptor is oxygen. Facultative anaerobes in oxygen conditions use the process of respiration, in anoxic conditions - fermentation. For obligate anaerobes, only fermentation is characteristic; under oxygen conditions, the death of the microorganism occurs due to the formation of peroxides, and cell poisoning occurs.

In the microbial cell, enzymes are biological catalysts. According to the structure, they distinguish:

1) simple enzymes (proteins);

2) complex; consist of protein (active center) and non-protein parts; required for enzyme activation.

There are also:

1) constitutive enzymes (they are constantly synthesized regardless of the presence of a substrate);

2) inducible enzymes (synthesized only in the presence of a substrate).

The set of enzymes in a cell is strictly individual for the species. The ability of a microorganism to utilize substrates through its set of enzymes determines its biochemical properties.

According to the place of action, there are:

1) exoenzymes (act outside the cell; take part in the process of disintegration of large molecules that cannot penetrate inside the bacterial cell; characteristic of gram-positive bacteria);

2) endoenzymes (act in the cell itself, provide the synthesis and breakdown of various substances).

Depending on the chemical reactions catalyzed, all enzymes are divided into six classes:

1) oxidoreductases (catalyze redox reactions between two substrates);

2) transferases (carry out intermolecular transfer of chemical groups);

3) hydrolases (perform hydrolytic cleavage of intramolecular bonds);

4) lyases (attach chemical groups at two bonds, and also carry out reverse reactions);

5) isomerases (carry out isomerization processes, provide internal conversion with the formation of various isomers);

6) ligases, or synthetases (connect two molecules, resulting in the splitting of pyrophosphate bonds in the ATP molecule).

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Metabolism (metabolism) of microorganisms

Nutrition of microbes (constructive metabolism).

Like all living things, the metabolism of microorganisms consists of two interrelated, simultaneously occurring, but opposite processes - anabolism, or constructive metabolism, and catabolism, or energy metabolism.

The metabolism of microorganisms has its own characteristics.

1) The speed and intensity of metabolic processes. During the day, a microbial cell can process such an amount of nutrients that exceeds its own weight by 30-40 times.

2) Expressed adaptability to changing environmental conditions.

3) Nutrition is carried out through the entire surface of the cell. Prokaryotes do not ingest nutrients, do not digest them inside the cell, but break them down outside the cell with the help of exoenzymes to simpler compounds that are transported into the cell.

For the growth and vital activity of microorganisms, the presence in the habitat of nutritious materials for building cell components and energy sources is essential. Microbes need water, sources of carbon, oxygen, nitrogen, hydrogen, phosphorus, potassium, sodium and other elements. Microelements are also required: iron, manganese, zinc, copper for the synthesis of enzymes. Different types of microbes require certain growth factors, such as vitamins, amino acids, purine and pyrimidine bases.

Depending on the ability to assimilate organic or non-organic sources of carbon and nitrogen, microorganisms are divided

into two groups - autotrophs and heterotrophs.

Autotrophs (Greek autos - himself, trophic - eating) receive carbon from carbon dioxide (CO 2) or its salts. From simple inorganic compounds, they synthesize proteins, fats, carbohydrates, enzymes.

Nutrient transport

Only small molecules penetrate the cell wall and cytoplasmic membrane into the prokaryotic cell, so proteins, polysaccharides and other biopolymers are first cleaved by exoenzymes to simpler compounds that are transported into the cell.

The penetration of nutrients into the cell occurs with the help of various mechanisms.

Passive diffusion - substances enter the cell due to diffusion along the concentration gradient, that is, due to the fact that the concentration outside the cell is higher than inside.

Facilitated diffusion - also occurs along a concentration gradient, but with the participation of carrier enzymes, the so-called permeases. This enzyme attaches molecules of a substance to itself on the outer side of the cytoplasmic membrane and gives it away on the inner side in an unchanged form. Then the free carrier moves again to the outer side of the membrane, where it binds new molecules of the substance. In addition, each permease carries a specific substance.

These two transfer mechanisms do not require energy costs.

Active transfer also occurs with the participation of permeases, and is carried out against the concentration gradient. A microbial cell can accumulate a substance at a concentration thousands of times higher than in the external environment. Such a process requires energy, that is, ATP is consumed.

Translocation of radicals is the fourth mechanism for the transfer of substances. This is an active transfer of chemically modified molecules, with the participation of permeases. For example, such a simple substance as glucose is transported in a phosphorylated form.

The release of substances from the bacterial cell occurs by passive diffusion or by facilitated diffusion with the participation of permeases.

Enzymes

Enzymes are catalysts for biological processes. A characteristic property of enzymes is their specificity. Each enzyme is involved only in a specific reaction with a specific chemical compound.

Enzymes that are secreted by a bacterial cell into the environment and carry out extracellular digestion are called exoenzymes. Exoenzymes also include beta-lactamase, which destroys penicillin and other beta-lactam antibiotics, protecting bacteria from their action.

Endoenzymes are involved in metabolic processes inside the cell.

Bacteria, due to their small size, are characterized by a high degree of self-regulation of enzyme production. In this regard, enzymes can be divided into constitutive and adaptive. Constitutive enzymes are constantly produced by the cell. Adaptive enzymes, in turn, are divided into inducible and inhibited. The production of inducible enzymes occurs in the presence of a substrate. For example, enzymes that break down lactose are formed in the cell only in the presence of this carbohydrate. The production of inhibited enzymes, on the contrary, is suppressed by the presence of a sufficiently high concentration of the final substrate in the medium (for example, tryptophan).

Many pathogenic bacteria, in addition to metabolic enzymes, secrete enzymes that are virulence factors. For example, such enzymes as hyaluronidase, collagenase, deoxyribonuclease, neuraminidase contribute to the penetration and spread of a pathogenic microbe in the body.

The ability of bacteria to produce certain enzymes is a feature so constant that it is used for identification, that is, determining the type of bacteria. Saccharolytic properties (fermentation of carbohydrates) and proteolytic properties (fermentation of proteins and peptone) are determined.

Microbes are characterized by high enzymatic activity. This is used in industry. In medicine, such therapeutic agents as streptokinase (streptococcal fibrinolysin), terrilitin (Aspergillus terricola protease) are used. Enzymes of microbial origin - lipases and proteases, which are part of detergents and washing powders, break down protein and fat contaminants to water-soluble substances that are easily washed off with water.

Biological oxidation (energy metabolism)

The process of biological oxidation provides the energy necessary for the life of the cell. The essence of the process lies in the sequential oxidation of substrates with the gradual release of energy. Energy is stored in ATP molecules.

Carbohydrates, alcohols, organic acids, fats and other substances undergo oxidation. But for most microorganisms, hexoses, in particular glucose, serve as an energy source.

Microorganisms have two types of biological oxidation: aerobic and anaerobic. With the aerobic type, oxygen is involved, and this process is called respiration in the strict sense of the word. With the anaerobic type of biological oxidation, the release of energy from organic molecules occurs without the participation of oxygen and is called fermentation.

The initial stage of anaerobic breakdown of glucose with the formation of pyruvic acid (PVA) occurs in the same way. This

acid is the central point from which the paths of respiration and many types of fermentation diverge.

In aerobic respiration, pyruvic acid enters the tricarboxylic acid cycle. Hydrogen PVC enters the respiratory chain. This is a chain of oxidative enzymes (cytochromes and cytochrome oxidase). Hydrogen is transferred along the chain of cytochromes and joins oxygen activated under the action of cytochrome oxidase with the formation of water. The end products of aerobic glucose oxidation are carbon dioxide (carbonic acid) and water. In the process of respiration, 38 ATP molecules are formed per molecule of glucose.

With the anaerobic type of biological oxidation, energy is generated as a result of fermentation. During alcoholic fermentation, PVC is ultimately converted into alcohol and carbon dioxide. The end product of lactic acid fermentation is lactic acid, butyric acid fermentation is butyric acid. During fermentation processes, only 2 ATP molecules are formed per molecule of glucose.

The microbial nature of fermentation was first discovered and proved by Pasteur. Studying butyric fermentation, Pasteur first encountered the possibility of life without oxygen, that is, with anaerobiosis. He also established the phenomenon, which was later called the "Pasteur effect": the cessation of the fermentation process with a wide access of oxygen.

Anaerobiosis exists only among prokaryotes. All micro-organisms according to the type of respiration are divided into the following groups: obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles.

Obligate aerobes reproduce only in the presence of free oxygen. These include Mycobacterium tuberculosis, Vibrio cholerae, miraculous wand. ,

Obligate or strict anaerobes receive energy in the absence of oxygen access. They have an incomplete set of redox enzymes, they do not have a cytochrome system, so they do not completely oxidize the substrate (glucose) to the final products - CO 2 and H 2 O. Moreover, in the presence of free oxygen, toxic compounds: hydrogen peroxide H 2 O 2 and free oxygen peroxide radical O 2. At the same time, aerobes do not die, since they produce enzymes that destroy these toxic compounds (superoxide dismutase and catalase). Spore-forming anaerobes under these conditions stop reproduction and turn into spores. Non-spore-forming anaerobes die even upon short-term contact with oxygen.

Obligate spore-forming anaerobes include Clostridia of tetanus, botulism, anaerobic wound infection; to non-spore-forming anaerobes - bacteroids, peptobacteria, bifidumbacteria.

Most pathogenic bacteria are facultative (conditional) anaerobes, such as enterobacteria. They have a complete set of enzymes and, with wide access to oxygen, oxidize glucose to final products; at a low oxygen content, they cause fermentation.

Microaerophiles multiply in the presence of small amounts of oxygen. For example, Campylobacter can multiply in 3-6% oxygen.

Growth and reproduction of microorganisms

The term "growth" refers to an increase in the size of a single individual, and "reproduction" - an increase in the number of individuals in a population.

Bacteria reproduce by binary fission in half, less often by budding. In gram-positive bacteria, a septum is formed from the cell wall and the cytoplasmic membrane, which grows inwards. In gram-negative bacteria, a constriction is formed, and then the cell divides into two individuals.

Cell division is preceded by the replication of the bacterial chromosome according to a semi-conservative type. In this case, the double-stranded DNA chain unwinds, each strand is completed with a complementary strand, and as a result, each daughter cell receives one parental strand and one newly formed one.

The speed of reproduction of different types of bacteria is different. Most bacteria divide every 15-30 minutes. Mycobacterium tuberculosis divides slowly - one division in 18 hours, spirochetes - one division in 10 hours.

If you sow bacteria in a liquid nutrient medium of a certain volume and then take a sample every hour and determine the number of living bacteria in such a closed environment and draw up a graph on which the time in hours is plotted along the abscissa axis, and the log-rhythm of the number along the ordinate axis live bacteria, we get a bacterial growth curve. The growth of bacteria is divided into several phases (Fig. 5):

1) latent phase (lag phase) - bacteria adapt to the nutrient medium, their number does not increase;

2) phase of logarithmic growth - the number of bacteria increases exponentially;

3) a phase of stationary growth, during which the number of newly formed bacteria is equalized by the number of dead ones, and the number of living bacteria remains constant, reaching a maximum level. This is the M-concentration - a value characteristic of each type of bacteria;

4) the dying phase, when the number of dying cells begins to prevail over the number of viable bacteria due to the accumulation of metabolic products and depletion of the environment.

The culture of bacteria in such a closed, unchanging environment is called periodic. If fresh nutrient medium is continuously fed into the seeded volume and the same amount of liquid is removed, then such a culture is called continuous. The number of living bacteria in such a culture will be constant at M-concentration. Continuous cultivation is used in the microbiological industry.

Formation of pigments, aromatic substances by microbes. Luminous microorganisms

Some types of microbes produce coloring substances - pigments. If the pigment is soluble in water, then both the colonies of microbes and the nutrient medium are colored. For example, the blue pigment secreted by Pseudomonas aeruginosa (Pseudomonas aeruginosa) stains the medium in Blue colour. Pigments that are soluble in organic solvents but insoluble in water do not color the nutrient medium. Such a red pigment, the so-called prodigiosan, soluble in alcohol, is secreted by the miraculous wand (Serratia marcescens). This group also includes pigments of yellow, orange, red color, characteristic of coccal air microflora. In some types of microbes, the pigments are so strongly associated with the protoplasm of the cell that they do not dissolve either in water or in organic solvents. Among pathogenic bacteria, such pigments of golden, fawn, lemon yellow color form staphylococci.

The color of the pigment is used to determine the type of bacteria.

Some microorganisms in the process of metabolism produce aromatic substances. For example, the smell of jasmine is typical for Pseudomonas aeruginosa. The characteristic smell of cheeses, butter, a special "bouquet" of wine is explained by the vital activity of microbes that are used to produce these products.

The glow (luminescence) of microbes occurs as a result of the release of energy during the biological oxidation of the substrate. The glow is the more intense, the stronger the influx of oxygen. Luminous bacteria were called photobacteria. They give a glow to the scales of fish in the sea, mushrooms, rotting trees, food products, on the surface of which they multiply. The glow can be observed at low temperatures, for example, in a refrigerator. Pathogenic for humans among photogenic bacteria has not been established.

The glow of food products caused by bacteria does not lead to their spoilage, and may even indicate that. that rotting does not occur in these products, since it stops with the development of putrefactive microorganisms.

CHAPTER 5

METHODS FOR CULTIVATION OF MICROORGANISMS. STUDY OF CULTURAL AND BIOCHEMICAL

PROPERTIES

Cultivation, that is, the cultivation of microorganisms in the laboratory, is used to study their properties and to obtain biomass. Bacteria, fungi, actinomycetes, spirochetes and some protozoa are cultivated on nutrient media. Chlamydia, rickettsiae, viruses and some protozoa can only reproduce in the animal organism or in living cells.

The cultural properties of this type of microorganisms are: 1) the conditions necessary for reproduction, and 2) the nature of growth on nutrient media. Cultural properties are one of the characteristics that are taken into account in the identification (species definition) of micro-organisms.

Nutrient media

Nutrient media must meet certain requirements. They must contain all the nutrients necessary for the reproduction of this type of microbe. Some pathogenic microorganisms grow on simple nutrient media, while others need the addition of blood, blood serum, and vitamins for their reproduction.

Culture media must be conditioned by the addition of sodium chloride or buffer solutions. For most bacteria, a nutrient medium containing 0.5% sodium chloride is favorable. The reaction of the nutrient medium, which is favorable for most of the pathogenic bacteria, is slightly alkaline, which corresponds to pH = 7.2-7.4. Vibrio cholerae grows at pH=7.8-8.5, mushrooms - at pH=5-5.5. Nutrient media should be moist, that is, contain a sufficient amount of water, be as transparent and sterile as possible, that is, do not contain microbes before sowing.

In terms of composition and origin, nutrient media are natural, artificial and synthetic. Natural nutrient media is a natural product, such as potatoes, other vegetables. Artificial nutrient media are prepared according to a certain recipe from products with the addition of organic and inorganic compounds. Synthetic media contain certain chemical compounds at known concentrations.

By consistency, nutrient media are liquid, semi-liquid, dense. As a sealant, agar-agar is usually used, a polysaccharide isolated from seaweed. Agar-agar is not used by microorganisms as a nutrient; it forms a gel in water that melts at 100°C and solidifies at 45°C.

To obtain a dense nutrient medium, agar-agar is added at a concentration of 1.5-2%, for semi-liquid - 0.5%.

According to the intended purpose, nutrient media can be divided into ordinary (simple), special, elective, differential diagnostic.

Conventional (simple) nutrient media are used for the cultivation of most microorganisms, these are meat-peptone broth (MPB), meat-peptone agar (MPA).

Special nutrient media are used for the cultivation of microorganisms that do not grow on simple media. For example, blood agar and sugar broth for streptococcus, serum agar for meningococcus and gonococcus.

Elective culture media are used to isolate one species from a mixture of different bacteria. This type bacteria grows on this medium faster and better than others, ahead of them in its growth; the growth of other bacteria is delayed on this medium. For example, clotted serum for diphtheria bacillus, alkaline peptone water for vibrio cholerae, bile broth for typhoid fever bacillus, saline media for staphylococcus aureus.

Differential diagnostic nutrient media are used to distinguish some types of bacteria from others by their enzymatic activity (see the relevant section).

Cultivation and isolation of pure cultures of aerobic bacteria

For the cultivation of microorganisms, certain conditions are necessary: ​​temperature, aerobic or anaerobic conditions.

The temperature should be optimal for this species. Most pathogenic bacteria multiply at 37°C. However, for some species, a lower temperature is optimal, which is associated with the peculiarities of their ecology. So, for the plague bacillus, whose natural habitat is rodents during hibernation, the optimum temperature is 28°C, as for leptospira, for botulism bacillus - 28°C-35°C.

In addition to the optimal temperature, for the cultivation of microorganisms, depending on the species, an aerobic or anaerobic environment is required.

In order to study the morphology, cultural, biochemical and other properties of microbes, it is necessary to obtain a pure culture. Usually, the culture of microbes is called their accumulation on a nutrient medium in the form of turbidity, near-bottom (parietal) growth or a film on the surface of a liquid medium or colonies on a dense medium. A separate colony is formed from one microbial cell. A pure culture is a culture of microbes of one species obtained from one colony. In laboratories, certain known strains of microbes are used for various studies. A strain is a pure culture of microbes obtained from a certain source, at a certain time, with known properties. As a rule, strains of microbes are designated by a specific number. For example, the Staphylococcus aureus 209P strain is used to determine the activity of penicillin.

The isolation of pure cultures of aerobes usually takes three days and is carried out according to the following scheme:

Day 1 - microscopy of a smear from the test material, stained (usually by Gram) - for a preliminary acquaintance with the microflora, which may be useful in choosing a nutrient medium for inoculation. Then inoculation of the material on the surface of the solidified nutrient agar to obtain isolated colonies. Sieving can be done according to the Drygalsky method on three Petri dishes with a nutrient medium. A drop of material is applied to the first cup and spread with a spatula over the entire cup. Then, with the same spatula, the culture remaining on it is distributed on the second cup and in the same way on the third. The greatest number of colonies will grow on the first cup, the least - on the third. Depending on how many microbial cells were in the test material, isolated colonies will grow on one of the cups.

The same result can be achieved by sieving on one cup. To do this, divide the cup into four sectors. The test material is inoculated with a bacteriological loop with strokes on the first sector, then, after calcining and cooling the loop, the seeding is distributed from the first sector to the second and in the same way sequentially to the third and fourth sectors. Isolated colonies are formed from individual microbial cells after daily incubation in a thermostat.

2nd day - study of the colonies grown on the plates, their description. Colonies can be transparent, translucent or opaque, they have different sizes, rounded regular or irregular outlines, convex or flat shape, smooth or rough surface, even or wavy, jagged edges. They can be colorless or have a white, golden, red, yellow color. Based on the study of these characteristics, the grown colonies are divided into groups. Then, an isolated colony is selected from the study group, a smear is prepared for microscopic examination in order to check the homogeneity of microbes in the colony. From the same colony, inoculation is carried out in a test tube with slanted nutrient agar.

3rd day - checking the purity of the culture grown on the slant agar by smear microscopy. With the homogeneity of the studied bacteria, the isolation of a pure culture can be considered complete.

To identify the isolated bacteria, cultural characteristics are studied, that is, the nature of growth on liquid and solid nutrient media. For example, streptococci on sugar broth form a near-bottom and parietal sediment, on blood agar - small, dotted colonies; cholera vibrio forms a film on the surface of alkaline peptone water, and on alkaline agar - transparent colonies; the plague bacillus on nutrient agar forms colonies in the form of "lace handkerchiefs" with a dense center and thin wavy edges, and in a liquid nutrient medium - a film on the surface, and then threads extending from it in the form of "stalactites".

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As first Let's take a system as an example... frequent cause of stomach disorders. Chapter... agricultural microbiology(St. Petersburg) and Czech microbiologists. ... M: Energoatomizdat, 1992 Atsyukovsky V.A. General etherodynamics. - M: Energoatomizdat, ...

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universities. The textbook contains seven parts. Partfirst - « Generalmicrobiology"- contains information about the morphology and physiology of bacteria ... Health Russian Federation in 1997. IN firstchapter contains a propaedeutic course and dietetics; in...