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GBOU VPO BSMU Ministry of Health of the Russian Federation

Department of Microbiology, Virology and Immunology

Head Departments: Tuygunov M.M.

Lecturer: Akhtarieva A.A.

Essay topic: "Metabolism of bacteria"

Completed: student l-205a

Samkova O.V.

Checked by: Akhtarieva A.A.

Introduction

Biochemical processes occurring in the cell are united by one word - metabolism(from the Greek. Metabole - transformation). This term is equivalent to the concept of "metabolism and energy". There are two aspects of metabolism: anabolism and catabolism.

Anabolism- a set of biochemical reactions that carry out the synthesis of cell components, i.e. that side of metabolism, which is called constructive metabolism.

catabolism- a set of reactions that provide the cell with the energy necessary, in particular, for constructive exchange reactions. Therefore, catabolism is also defined as the energy metabolism of the cell.

In a constructive exchange, two groups of biosynthetic processes can be distinguished: the biosynthesis of monomers (amino acids, nucleotides, monosaccharides, fatty acids) and the biosynthesis of polymers (proteins, nucleic acids, polysaccharides and lipids). About 70 different precursor monomers are needed for their synthesis. In addition to them, the cell must synthesize a number of compounds that play a catalytic role. The synthesis of any monomer occurs (in the presence of carbon and energy sources) through a chain of successive biochemical reactions catalyzed by specific proteins - enzymes. In turn, the synthesis of biopolymers also requires the participation of specific proteins. Therefore, the basis of constructive metabolism is the biosynthesis of proteins, which is under the control of the genetic system of the body.

Features of metabolism in bacteria

Features of metabolism in bacteria are that:

* its intensity is quite high, which is probably due to a much larger ratio of surface to unit mass than that of multicellular organisms;

* dissimilation processes prevail over assimilation processes;

* the substrate spectrum of substances consumed by bacteria is very wide - from carbon dioxide, nitrogen, nitrites, nitrates to organic compounds, including anthropogenic substances - environmental pollutants (thus ensuring the processes of its self-purification);

* bacteria have a very wide range of different enzymes - this also contributes to the high intensity of metabolic processes and the breadth of the substrate spectrum.

Bacterial enzymes are divided into 2 groups according to localization:

* exoenzymes - bacterial enzymes secreted into the external environment and acting on the substrate outside the cell (proteases, polysaccharides, oligosaccharidases);

* endoenzymes - bacterial enzymes that act on substrates inside the cell (cleaving amino acids, monosaccharides, synthetase).

The synthesis of enzymes is genetically determined, but the regulation of their synthesis is due to direct and feedback, i.e. for some it is repressed, and for others it is induced by the substrate. Enzymes whose synthesis depends on the presence of an appropriate substrate in the medium (beta-galactosidase, beta-lactamase) are called inducible.

Another group of enzymes, the synthesis of which does not depend on the presence of a substrate in the medium, is called constitutive (glycolysis enzymes). Their synthesis always takes place, and they are always contained in microbial cells in certain concentrations. They study the metabolism of bacteria using physicochemical and biochemical research methods in the process of cultivating bacteria under certain conditions on special nutrient media containing a particular compound as a substrate for transformation.

This approach makes it possible to judge the metabolism through a more detailed study of the processes of various types of metabolism (proteins, carbohydrates) in microorganisms.

In most cases, the same substance is used in both assimilation and dissimilation. The exceptions are carbohydrates, which are cleaved and do not take part in constructive metabolism.

Metabolism in microorganisms is characterized by intensive consumption of nutrients. So, under favorable conditions, during the day, one bacterial cell assimilates substances 30-40 times more than its mass.

Various chemicals are involved in the metabolism. Depending on this, protein, carbohydrate, lipid and water-salt metabolism are distinguished.

Protein metabolism. Protein breakdown first occurs to peptonosis under the action of exoprotease enzymes. In the future, peptones under the influence of endoproteases are cleaved to amino acids that enter the cell. Here amino acids can undergo deamination and decarboxylation.

As a result of deamination, ammonia, keto acids or hydroxy acids, alcohol and other substances are formed.

Decarboxylation of amino acids occurs during the development of putrefactive bacteria with the formation of toxic products of "cadaveric poisons". Histidine is decarboxylated to form histamine, ornithine to putrescine, lysine to cadaverine, and tyrosine to tyramine. Some microbes produce the enzyme tryptophanase, under the influence of which the amino acid tryptophan breaks down to form indole. The presence of indole formation is used in the identification of microorganisms.

Along with the reactions of protein cleavage, the processes of their synthesis also occur. Bacteria use amino acids to build proteins. Bacterial cells satisfy their needs for amino acids in two ways: some microorganisms obtain amino acids from protein breakdown, while others synthesize them from simple nitrogen compounds. An important property of microbes is the ability to synthesize essential amino acids (methionine, tryptophan, lysine). Protein synthesis takes place in the ribosomes of the cell.

Protein metabolism is closely related to carbohydrate metabolism. Pyruvic acid is used to build protein compounds, and dicarboxylic acids are active mediators in the biosynthesis of amino acids.

carbohydrate metabolism. Carbohydrates are broken down by enzymes to form glucose and maltose. Under the influence of the enzymes maltase, sucrase, lactase, disaccharides that have entered the bacterial cell are hydrolyzed and decomposed into monosaccharides, which are then fermented to break the chain of carbohydrate molecules and release a significant amount of energy.

The breakdown of carbohydrates by microbes is accompanied by the formation of organic acids, which can decompose to final products - CCL and H2O.

The synthesis of carbohydrates in microorganisms occurs photo- and chemosynthetically. During photosynthesis, green and purple bacteria containing pigments such as chlorophyll synthesize glucose from carbon dioxide in the air. At the same time, light energy is necessary for the flow of ndothermic reactions of synthesis.

The process of photosynthesis in bacteria (prokaryotes) is different from photosynthesis in green plants (eukaryotes). In plants, during photolysis, water serves as a hydrogen donor, as a result of which molecular oxygen is released.

In prokaryotes, with the exception of blue-green algae, hydrogen donors are H2S, H2, and other mineral and organic compounds; therefore, oxygen is not formed as a result of the photosynthesis reaction. The main pigment of photosynthesis in bacteria is bacteriochlorophyll, in green plants - chlorophyll, located in chloroplasts, each of which is equivalent to a prokaryotic cell. Bacteria do not have chloroplasts.

Chemosynthesis is carried out by microorganisms that synthesize carbohydrates from glucose, which is previously formed as a result of saccharolytic reactions, i.e., the breakdown of complex sugars. For chemosynthesis, chemical energy is used, released during the breakdown of adenosine triphosphoric acid (ATP), i.e., the energy of chemical reactions.

lipid metabolism includes the processes of lipid hydrolysis, the absorption of fatty acids and monoglycerides, the biosynthesis of specific lipids, their breakdown and the release of end products of decomposition.

Most bacterial species metabolize lipids in the form of glycerol, which serves as an energy source. Microorganisms also use it for the synthesis of lipids, which, in the form of inclusions, are reserve nutrients (nutrient material).

The main processes of lipid metabolism are carried out with the help of lipase and other lipolytic enzymes that are firmly associated with the cell cytoplasm.

Water-salt exchange includes the intake and release of water and mineral salts, as well as the transformations that occur with them.

Only a small number of elements in the Periodic Table of D.I. Mendeleev is required by microorganisms in relatively high concentrations - these are the ten main biological elements (macroelements): C, O, H, N, S, P, K, Mg, Ca, Fe. The main components of organic compounds are the first four elements - organogens.

Sulfur is required for the synthesis of the amino acids cysteine and methionine and some enzymes. Phosphorus is a constituent of nucleic acids, phospholipids, teichoic acids, and many nucleotides. The remaining four elements are metal ions used as cofactors for enzymes, as well as components of metal complexes.

In addition to the listed main elements, microorganisms require ten more trace elements: Zn, Mn, Na, CI, Mo, Se, Co, Cu, W, Ni, which are involved in the synthesis of enzymes and activate them.

From various elements and their compounds, microorganisms synthesize proteins, nucleoproteins, glucidolipid-protein complexes, nucleic acids, enzymes, vitamins, etc.

Types of biological oxidation in bacteria

The synthesis of biopolymers of bacteria cells requires energy. It is formed during biological oxidation and is stored in the form of macroergic molecules - ATP and ADP. Respiratory organelles in most are derivatives of the cytoplasmic membrane - mesosomes, but which are localized special respiratory enzymes such as cytochrome oxidases. The type of biological oxidation is one of the key features that allow differentiating different microorganisms. On this basis, 3 groups of bacteria are distinguished:

1) Obligate aerobes - they are able to obtain energy only through respiration and need oxygen molecules as the final electron acceptor. As a type of redox processes, they are characterized by oxidation, in which oxygen is the final electron acceptor.

2) Obligate anaerobes are bacteria that can grow only in an oxygen-deprived environment, for them, as a type of OVR, fermentation character, in which an electron is transferred from the donor substrate to the acceptor substrate.

3) Facultative anaerobes are bacteria that grow in both oxygen and oxygen-free environments. As electron acceptors, they test both oxygen molecules and organic compounds. Among them may be: A) facultative anaerobic bacteria that can switch from oxidation to fermentation, these include enterobacteria. B) aerotolerant facultative anaerobic bacteria that can grow in the presence of atmospheric oxygen, but do not use it, but obtain energy exclusively through fermentation, they include lactic acid bacteria.

bacteria synthesis metabolism exchange

protein synthesis

Protein synthesis ( broadcast) is the most complex of biosynthetic processes: it requires a very large number of enzymes and other specific macromolecules, the total number of which, apparently, reaches three hundred. Some of them are also combined into a complex three-dimensional structure of ribosomes. But despite the great complexity, the synthesis proceeds at an extremely high speed (tens of amino acid residues per second). The process can be slowed down and even stopped by antibiotic inhibitors.

In the fifties of the XX century, it was found that protein synthesis occurs in ribonucleoprotein particles called ribosomes. The diameter of the ribosome of the bacterium E. coli is 18 nm, and their total number is tens of thousands in a cell. Eukaryotic ribosomes are somewhat larger (21 nm). The process itself takes place in five stages.

1. Activation of amino acids. Each of the 20 amino acids of a protein is covalently bonded to a specific tRNA using the energy of ATP. The reaction is catalyzed by specialized enzymes that require the presence of magnesium ions.

2. Protein chain initiation. An mRNA containing information about a given protein binds to a small particle of the ribosome and to an initiating amino acid attached to the corresponding tRNA. t-RNA is complementary to the triplet that is part of the i-RNA, signaling the beginning of the protein chain.

3. Elongation. The polypeptide chain is lengthened due to the sequential attachment of amino acids, each of which is delivered to the ribosome and inserted into a specific position using the corresponding t-RNA. At present, the genetic code is completely deciphered, that is, triplets of nucleotides are assigned to all amino acids. Elongation is carried out with the help of cytosolic proteins (the so-called elongation factors).

4. Termination. After completion of the synthesis of the chain, which is signaled by another special codon of i-RNA, the polypeptide is released from the ribosome.

5. Folding and processing. To take its usual shape, the protein must fold, forming a certain spatial configuration. Before or after folding, the polypeptide may undergo processing carried out by enzymes and consisting in the removal of excess amino acids, the addition of phosphate, methyl and other groups, etc.

Protein synthesis requires a lot of energy - 24.2 kcal/mol. After the synthesis is completed, the protein is delivered to its destination with the help of a special polypeptide leader.

Protein synthesis is controlled operator genes. The set of working genes - operators and structural genes - is called operon. Operons are not an independent system, but "obey" regulator genes responsible for the start or stop of the operon. Regulatory genes carry out their control with the help of a special substance, which they synthesize if necessary. This substance reacts with the operator and blocks it, which entails the termination of the operon. If the substance reacts with small molecules - inductors, this will be a signal to resume the system.

The operon model was developed on microorganisms, but it also corresponds to the principle of operation of the eukaryotic genome. In the latter, genes form complex systems called supergenes, which can simultaneously encode many identical protein molecules.

Features of energy metabolism

ATP molecules are synthesized as a result of electron transfer from its primary donor to the final acceptor. Depending on what is the final electron acceptor, aerobic and anaerobic respiration are distinguished. During aerobic respiration, molecular oxygen serves as the final electron acceptor, and during anaerobic respiration, various inorganic compounds. Thus, energy is mobilized in oxidation and reduction reactions. Oxidation is the release of electrons, reduction is the addition of electrons. When the removal of a pair of electrons or hydrogen atoms from an organic substrate is associated with the reduction of oxygen to water, this is accompanied by a significant change in free energy. It is approximately equal to the change in energy during the combustion of one molecule of hydrogen.

The transfer of electrons along the chain allows this energy to be released in portions and convert some of it into energy-rich ATP bonds. For such a transport chain to function, there must be a gradient in its oxidative capacity. The ability of a substance to donate or add an electron (i.e., to be oxidized or reduced) is quantified as its redox potential.

The electron carriers in the chain of their transfer participate in successive reactions with gradually increasing values and an increase in the redox potential. Bacteria have a variety of variations on this general pattern. In this regard, they are divided into the following four groups according to the type of breathing:

1) strict aerobes (reproduce only in the presence of oxygen);

2) microaerophiles (need a reduced concentration of free oxygen);

3) facultative anaerobes (they can consume glucose and reproduce both in aerobic and anaerobic conditions);

4) strict anaerobes (reproduce only in anoxic conditions, i.e., do not use oxygen as the final electron acceptor).

The maximum mobilization of energy from glucose occurs when it is oxidized through the citric acid cycle (Krebs cycle). One mole of glucose contains about 690 kcal (this amount of energy is released when 180 g of glucose is burned). At the first stage of glucose consumption in the absence of oxygen (during glycolysis), two molecules of lactic acid are formed from one of its molecules and only two molecules of ATP are synthesized. Each ATP molecule has one energy-rich (10 kcal) pyrophosphate chemical bond. After the breakdown of glucose to lactic acid, the latter is oxidized in the presence of oxygen and turns into pyruvic acid, which is then completely oxidized through the Krebs cycle. Each lactate (pyruvate) molecule donates 6 pairs of electrons. During the transfer of each pair of electrons along the transfer chain, part of their energy is used to form 3 ATP molecules.

Thus, the complete oxidation of one mole of glucose is accompanied by the synthesis of 38 ATP molecules with a total energy reserve of 380 kcal, or about 55% of the total energy of a mole of glucose (690 kcal); the rest of the energy undergoes dissipation, i.e., useless dissipation in the form of heat. However, this output of useful energy is quite high. The yield for many bacteria is known, as is the yield of cells, which is about 10 g of dry matter per 1 mole of ATP formed. To explain the mechanism of energy mobilization, i.e., the synthesis of ATP during electron transfer, a number of hypotheses have been proposed, including the Mitchell chemo-osmotic hypothesis. It proceeds from the fact that the electron transport chain localized in the membrane (in bacteria in the CM) is oriented across it, and electrons are transferred sequentially from one carrier to another in the direction of an increasing redox potential.

The oxidation of electron carriers is accompanied by the simultaneous transfer of protons (H+) from the inner surface of the membrane to its outer surface. Because the membrane is otherwise impermeable to protons, a proton concentration gradient (pH+) develops between the inner and outer layers of the membrane and it becomes "energized". The energy of the proton gradient is used by the cell for various processes, including active nutrient transport, flagellar rotation, and ATP synthesis.

The Embden--Meyerhoff pathway is most widely used by various bacteria when consuming glucose. From the resulting final product, pyruvic acid, as well as from such intermediate products as erythrose-4-phosphate and ribose-5-phosphate, there are various metabolic pathways for the synthesis of twenty amino acids. Since much more energy is released under aerobic conditions than during fermentation, some bacteria perform a type of respiration in which bound oxygen is an acceptor of hydrogen (electrons). Its carriers are nitrates (nitrate respiration) or sulfates (sulfate respiration). At the same time, due to the hydrogen of the oxidized substrate, nitrates are reduced to molecular nitrogen. The ability of such bacteria to transfer electrons to nitrates and sulfates is associated with the presence of cytochromes and an electron transport system in them. This allows them to carry out a fairly complete oxidation of the substrate and receive in this way much more energy than during fermentation.

References

1. "Medical microbiology, immunology and virology" A.I. Korotyaev, S.A. Babichev. Textbook for medical schools.

2. Lectures on microbiology http://bsmy.ru/1593

3. http://bibliofond.ru

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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 cleavage, 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.

Energy metabolism of microorganisms

2. Constructive metabolism

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

The generalized conditional scheme of the biosynthesis of complex organic compounds is shown below, where the following main stages are distinguished: the formation of organic precursors from the simplest inorganic substances (I), from which “building blocks” (II) are synthesized at the next stage. In the future, 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" - himself, "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" - a 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 the natural nutrition of microbes, and some are 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 saturating the cell with nutrients, simple diffusion is of little importance. However, this is the way water molecules enter the cell. An important role in 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 external environment. Active transfer is the main mechanism for the entry of nutrients into cells with saprozoic nutrition.

Consider the first group of genes. Ethanol is oxidized in two steps and two key enzymes work in these two steps. First, ethanol is converted to acetaldehyde by the enzyme alcohol dehydrogenase.

Genetics and biochemistry of alcoholism

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Hydrophilic hormones, their structure and biological functions

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Study of the seasonal biorhythm of bacillary-coccal transformation of the bacterium Helicobacter pylori

The bacterium Helicobacter pylori has very successfully adapted to life in the extreme conditions of the human stomach. It is gram-negative, which already implies a powerful impenetrable cell wall. It is able to live in microaerophilic conditions...

Morphology and metabolism of yeast

Regulation of primary metabolic processes

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The role of peptides in the functioning of the nervous system

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Free amino acids of the nervous system

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Structure and transport of androgens

In target organs, there are separate, specific cytoreceptors of sex hormones. These hormone receptors are, obviously, the tissue component of every endocrine function - including the gonadal ...

Physiology and biochemistry of plant components

The Hatch and Slack cycle is also found in succulent plants. But if in C4 plants cooperation is achieved due to the spatial separation of two cycles (incorporation of CO2 into organic acids in the mesophyll, reduction in the lining)...

All listed in the table. 1 photosynthetic microorganisms are adapted to the use of visible light (wavelength 400--700 nm) and the near infrared part of the spectrum (700--1100 nm) ...

Energy metabolism of microorganisms

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...

Energy metabolism of microorganisms

Most heterotrophic organisms obtain 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 ...

Energy metabolism of microorganisms

Oxidation of reduced mineral compounds of nitrogen, sulfur, iron serves as an energy source for chemolithotrophic microorganisms...

3. Metabolism of bacteria

Metabolism (metabolism) of bacteria is totality two interconnected opposite processes of catabolism and anabolism.

catabolism (dissimilation) - decay of substances in the process of enzymatic reactions and the accumulation of energy released during this in ATP molecules.

Anabolism (assimilation) - synthesis of substances with the expenditure of energy.

Bacterial metabolism is characterized by:

Its intensity is enough high level, which is possibly due to a much larger ratio of surface to unit mass than that of multicellular organisms;

Processes dissimilation take precedence over processes assimilation;

substrate spectrum substances consumed by bacteria is very wide - from carbon dioxide, nitrogen, nitrites, nitrates to organic compounds, including anthropogenic substances - environmental pollutants (thus ensuring the processes of its self-purification);

Bacteria are very a wide range of different enzymes- this also contributes to the high intensity of metabolic processes and the breadth of the substrate spectrum.

bacterial enzymes according to localization are divided into 2 groups:

exoenzymes- bacterial enzymes released into the external environment and acting on the substrate outside the cell (for example, proteases, polysaccharides, oligosaccharidases);

endoenzymes- enzymes of bacteria that act on substrates inside the cell (for example, enzymes that break down amino acids, monosaccharides, synthetases).

Synthesis of enzymes genetically determined, but regulation their synthesis is through direct and feedback, i.e. for some it is repressed, while for others it is induced by the substrate. Enzymes whose synthesis depends on the presence of an appropriate substrate in the medium (for example, beta-galactosidase, beta-lactamase) are called inducible .

Another group of enzymes the synthesis of which does not depend on the presence of a substrate in an environment called constitutive (e.g. glycolysis enzymes). Their synthesis always takes place, and they are always contained in microbial cells in certain concentrations.

Studying the metabolism of bacteria physicochemical and biochemical methods research in the process of cultivating bacteria under certain conditions on special nutrient media containing one or another compound as a substrate for transformation. This approach makes it possible to judge the metabolism through a more detailed study of the processes of various types of metabolism (proteins, carbohydrates) in microorganisms.

Question 5. Features of protein and carbohydrate metabolism in bacteria

1. Protein metabolism

Protein metabolism in bacteria, on the one hand, process of synthesis of own amino acids and proteins by assimilating the necessary components from the external environment, and on the other hand, extracellular protein breakdown under the influence of various enzymes. If protein breakdown occurs under anaerobic conditions, then this process is called decay and if he goes in aerobic conditions smoldering.

If bacteria have proteases, proteins are cleaved by them to intermediate decomposition products - peptones, and if bacteria have peptidases, peptones are cleaved by them to amino acids and their decay products (ammonia, hydrogen sulfide, indole). Proteolytic(ability to break down proteins) and peptolytic(the ability to break down peptones) properties are not expressed in all bacteria, so their study in conjunction with other enzymatic properties helps to identify bacteria.

2. Carbohydrate metabolism

carbohydrate metabolism Bacteria also has a dual character - it is the process of synthesis and breakdown of carbohydrates. Breakdown of carbohydrates by bacteria (saccharolytic properties) under aerobic conditions with the formation of carbon dioxide and water is called burning , a split them carbohydrates under anaerobic conditions - fermentation.

Depending on the nature of the end products of carbohydrate decomposition under anaerobic conditions, fermentation is distinguished:

Alcohol,

lactic acid,

propionic acid,

Formic acid,

Butyric,

Acetic acid.

Molecular oxygen does not participate in fermentation processes. Most fermenting bacteria are obligate anaerobes. However, some of them are facultative anaerobes, are able to carry out the fermentation process in the presence of oxygen, but without its participation. Moreover, this oxygen inhibits the fermentation process. And it is replaced by combustion (respiration - the final acceptor of hydrogen - oxygen). This effect has been called Pasteur effect and is one of classical examples of the change in metabolism in bacteria depending on environmental conditions.

3. Types of biological oxidation in bacteria

Synthesis of biopolymers the bacterial cell requires energy. It is formed during biological oxidation and stored in the form macroerg molecules- ATP and ADP.

Respiratory organelles in most bacteria are derivatives of the cytoplasmic membrane - mesosomes , which are localized special respiratory enzymes such as cytochrome oxidases. Type of biological oxidation is one of the key features that allow differentiating different microorganisms. On this basis there are three groups of bacteria:

The first group - obligate aerobes , which are able to obtain energy only by breathing and need molecular oxygen as the final electron acceptor. As a type of redox processes, they are characterized by oxidation, in which oxygen is the final electron acceptor.

The second group - obligate anaerobes - bacteria able to grow only in an environment deprived of oxygen. For them, as a type of redox processes, fermentation is characteristic, in which electrons are transferred from the donor substrate to the acceptor substrate.

The third group - facultative anaerobes - bacteria able to grow in the presence or absence of oxygen, and use both molecular oxygen and organic compounds as terminal electron acceptors.

Among them may be facultative anaerobic bacteria, capable of switching from oxidation to fermentation (enterobacteria), as well as aerotolerant facultative anaerobic bacteria, which can grow in the presence of atmospheric oxygen, but do not use it, but obtain energy exclusively through fermentation (for example, lactic acid bacteria).

Question 6. Growth and reproduction. Genetics of bacteria

1. Growth and reproduction of bacteria

For microbiological diagnostics, the study of microorganisms and in biotechnological purposes microorganisms are cultivated on artificial X nutrient media.

Under bacteria 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.

Increasing the number of cells in a population microorganisms are referred to as "reproduction" . It is characterized by the generation time (the time interval during which the number of cells doubles) and such a concept as the concentration of bacteria (the number of cells in 1 ml).

Unlike the mitotic cycle of division in eukaryotes, the reproduction of most prokaryotes (bacteria) proceeds by binary fission, a actinomycetes - budding. Moreover, all prokaryotes exist in haploid state, since the DNA molecule is represented in the cell in the singular.

2. Bacterial population. The colony

When studying the process of reproduction of bacteria, it must be taken into account that bacteria always exist in the form of more or less numerous populations, and the development of a bacterial population in a liquid nutrient medium in batch culture can be considered as a closed system. There are 4 phases in this process:

1st - initial, or lag phase , or the reproduction delay phase, it is characterized by the onset intensive cell growth, but the rate of their division remains low;

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

3rd - stationary phase , it occurs when the number of cells in the population ceases to increase. This is due to what is coming balance between the number of newly formed and dying cells. The number of living bacterial cells in the population per unit volume of the nutrient medium in the stationary phase is denoted as M-concentration . This indicator is a characteristic feature for each type of bacteria;

4th - dying phase (logarithmic death), which is characterized by the predominance of the number of dead cells in the population and progressive a decrease in the number of viable cells in the population.

The cessation of growth in the number (reproduction) of the population of microorganisms occurs in connection with nutrient depletion and/or accumulation in it metabolic products microbial cells. Therefore, 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 an open biological system that seeks to eliminate the dynamic balance at a certain level of population development. This process of growing microorganisms is called flow culture(continuous culture). Growth in 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 to obtain various biologically active substances produced by microorganisms.

To study metabolic processes throughout the cell division cycle, it is also possible to use synchronous cultures. Synchronous cultures - cultures of bacteria, all members of the population of which are in the same phase of the cycle. This is achieved with the help of special cultivation methods, however, after several simultaneous divisions, the synchronized cell suspension gradually switches back to asynchronous division, so that the number of cells no longer increases stepwise, but continuously.

When cultivated on dense nutrient media, bacteria form colonies . This is an accumulation 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:

value,

Transparency

height,

The nature of the surface

Consistency.

The nature of the colonies is one of taxonomic features of bacteria.

3. Genetics of bacteria

The most important feature of living organisms is variability and heredity. The basis of the hereditary apparatus of bacteria, like all other organisms, is DNA (for RNA-containing viruses - RNA ).

Along with this, the hereditary apparatus of bacteria and the possibility of studying it have a number of features. First of all, bacteria haploid organisms, i.e. they have one chromosome. In this regard, when inheriting traits, there is no phenomenon dominance. Bacteria have a high rate of reproduction, and therefore, in a short period of time (day), several tens of generations of bacteria are replaced. This makes it possible to study huge populations and easily identify even rare mutations.

hereditary apparatus bacteria is represented chromosome. Bacteria have only one. If there are cells with two or four chromosomes, then they are the same. bacteria chromosome - This DNA molecule. The length of this molecule reaches 1.0 mm and, in order to "fit" in a bacterial cell, it is not linear, as in eukaryotes, but supercoiled in loops and folded into a ring. This ring at one point is attached to the cytoplasmic membrane.

Individual chromosomes are located on the bacterial chromosome genes. In Escherichia coli, for example, there are more than 2 thousand of them. However genotype (genome) of bacteria is represented not only by chromosomal genes. The functional units of the bacterial genome, in addition to chromosomal genes, are IS sequences, transposons and plasmids.

Question 7. Functional units of the genome. Bacterial cell variation

1. Functional units of the genome

IS sequences - short fragments of DNA. They do not carry structural (coding for a particular protein) genes, but contain only genes responsible for transposition(the ability of IS sequences to move along the chromosome and integrate into its various parts). IS sequences are the same in different bacteria.

transposons . These are DNA molecules - larger than IS sequences. In addition to the genes responsible for transposition, they contain a structural gene, which encodes one or another feature. Transposons move easily along the chromosome. Their position affects expression both their own structural genes and neighboring chromosomal ones. Transposons can also exist outside the chromosome, autonomously, but are not capable of autonomous replication.

Plasmids - This circular supercoiled DNA molecules. Their molecular weight varies widely and can be hundreds of times greater than that of transposons. Plasmids contain structural genes, endowing the bacterial cell with different, very properties that are important to her.:

R-plasmids - drug resistance,

Col-plasmids - to synthesize colicins,

F-plasmids - to transfer genetic information,

Hly-plasmid - to synthesize hemolysin,

Tox-plasmid - to synthesize a toxin,

Biodegradation plasmids - destroy one or another substrate and others.

Plasmids can be integrated into the chromosome(unlike IS sequences and transposons, they are embedded in strictly defined areas) and may exist offline. In this case, they have the ability for autonomous replication, and that is why there can be 2, 4, 8 copies of such a plasmid in a cell.

Many plasmids contain genes transmissibility and are able to be transferred from one cell to another during conjugation (exchange of genetic information). Such plasmids are called transmissible.

2. Fertility factor

The presence of the F-plasmid ( fertility factor, sex factor ) gives bacteria the functions of a donor, and such cells are able to transfer their genetic information to others, F cells. Thus, the presence of the F-plasmid is the genetic expression of sex in bacteria. Not only donor function is associated with the F-plasmid, but also some other phenotypic features. This is, first of all, the presence of F-piles ( genital cilia), with the help of which contact is established between donor and recipient cells. Through their channel, donor DNA is transmitted during recombination. Receptors for male fi-phages are located on the genital cilia. F cells do not have such receptors and are not sensitive to such phages.

Thus, the presence of F-cilia and sensitivity to fi-phages can be considered as a phenotypic expression (manifestation) of sex in bacteria.

3. Variability

Bacteria are distinguished two types of variability - phenotypic and genotypic.

Phenotypic variability – modifications- does not affect the genotype. Modifications affect most of the individuals in the population. They are not inherited and fade over time, i.e., return to the original phenotype through a larger (long-term modifications) or fewer (short-term modifications) number of generations.

Genotypic variability affects the genotype. It is based on mutations and recombinations.

Mutations bacteria are not fundamentally different from mutations in eukaryotic cells. Mutations in bacteria are relative ease of detection, as it is possible to work with large populations of bacteria . By origin, mutations can be:

spontaneous

induced.

By length:

Point,

Chromosomal mutations.

By direction:

Back mutations.

recombinations in bacteria different from recombination in eukaryotes:

First, bacteria have several mechanisms recombination (exchange of genetic material).

Secondly, during recombination in bacteria, not a zygote is formed, as in eukaryotes, but merozygote (carries the complete genetic information of the recipient and part of the genetic information of the donor in the form of a supplement).

Thirdly, during recombinations in a bacterial recombinant cell not only the quality, but also the quantity of genetic information changes.

Transformation introduction of the finished DNA preparation into the recipient bacterial cell(specially prepared or directly isolated from the donor cell). Most often, the transfer of genetic information occurs when the recipient is cultivated on a nutrient medium containing the donor's DNA.

For the perception of donor DNA during transformation, the recipient cell must be in a certain physiological state ( competence), which is achieved by special methods of processing the bacterial population. During transformation, single (more often one) signs are transmitted. Transformation is the most objective evidence of the association of DNA or its fragments with one or another phenotypic trait, since a pure DNA preparation is introduced into the recipient cell.

transduction is the exchange of genetic information between bacteria transmission from donor to recipient with moderate(transducing)bacteriophages.

Transducing phages can carry one or more genes (traits). Transduction happens:

Specific (always the same gene is transferred),

Non-specific (different genes are transmitted).

It's connected with localization transducing phages in the donor genome. In the first case, they are always located in one place on the chromosome, in the second, their localization is not constant.

Conjugation - this is the exchange of genetic information in bacteria by transferring it from a donor to a recipient at them direct contact.

After formation between donor and recipient conjugation bridge one strand of donor DNA enters the recipient cell through it. The longer the contact, the more of the donor DNA can be transferred to the recipient. Based on the interruption of conjugation at certain intervals, it is possible to determine the order of the genes on the chromosome of bacteria - to build chromosome maps bacteria (to bacteria artery). Donor function have F + cells.

Question 8. Normal microflora of the human body

1. The concept of microbiocenosis

Normal microflora accompanies its owner throughout his life. Its essential importance in maintaining the vital activity of the body is evidenced by observations of gnotobiont animals(devoid of their own microflora), whose life is significantly different from that of normal individuals, and sometimes simply impossible. In this regard, the doctrine of the normal human microflora and its violations is a very significant section of medical microbiology.

It is now firmly established that organism humans and the micro-organisms that inhabit them are single ecosystem. From modern positions normal microflora should be considered as collection of many microbiocenoses , characterized by a certain species composition and occupying one or another biotype in the body. In any microbiocenosis it is necessary to distinguish between constantly occurring types of microorganisms - characteristic (indigenous, autochthonous flora), additional and random - transient (allochthonous Flora). The number of characteristic species is relatively small, but numerically they are always represented most abundantly. The species composition of transient microorganisms is diverse, but they are not numerous.

The surfaces of the skin and mucous membranes of the human body are abundantly populated by bacteria. At the same time, the number of bacteria inhabiting the integumentary tissues (skin, mucous membranes) is many times greater than the number of the host's own cells. The quantitative fluctuations of bacteria in the biocenosis can reach several orders of magnitude for some bacteria and, nevertheless, fit into the accepted standards. The formed microbiocenosis exists as a whole as a community of united food chains and related microecology types.

The totality of microbial biocenoses found in the body of healthy people constitutes the normal human microflora. At present, the normal microflora is considered as an independent extracorporeal organ. It has a characteristic anatomical structure ( biofilm) and it has certain functions. It has been established that the normal microflora has a sufficiently high species and individual specificity and stability.

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 mandatory. 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) the 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 blue. 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 of 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 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; a 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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Literature

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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2. Constructive metabolism

3. Metabolism of bacteria

Question 5. Features of protein and carbohydrate metabolism in bacteria

1. Protein metabolism

2. Carbohydrate metabolism

3. Types of biological oxidation in bacteria

Question 6. Growth and reproduction. Genetics of bacteria

1. Growth and reproduction of bacteria

2. Bacterial population. The colony

3. Genetics of bacteria

Question 7. Functional units of the genome. Bacterial cell variation

1. Functional units of the genome

2. Fertility factor

3. Variability

Question 8. Normal microflora of the human body

1. The concept of microbiocenosis

Chapter 4 breakthrough technologies in life support systems contents of chapter 4 1 human life support

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