All life-support reactions occurring in a microbial cell and catalyzed by enzymes constitute metabolism, or metabolism. Intermediate or final products formed in the appropriate sequence of enzymatic reactions, as a result of which the covalently bound skeleton of a particular biomolecule is destroyed or synthesized, are called metabolites.

In the metabolism of microorganisms, two opposing and at the same time unified processes are continuously carried out: anabolism and catabolism. In other words, the exchange is constructive and energetic. In the first case, metabolism proceeds with the absorption of free energy while consuming a relatively small volume of nutrient material; in the second, the process of releasing free energy occurs, which consumes a huge mass of nutrient substrate.

Based on the type of nutrition, living beings are divided into two groups: holozoic and holophytic. The holozoic type of nutrition is characteristic of animals (from higher to simplest). Microbes belong to the holophytic type of nutrition. They do not have organs for eating, and their nutrients penetrate through the entire surface of the body.

There are several mechanisms for feeding microbial cells. Nutrients can enter the microbial cell from the external environment through the cell wall, capsule, mucous layers and cytoplasmic membrane. Metabolic products, i.e. substances that are unnecessary and harmful to microorganisms, are also released through these same structures. The mechanism of such nutrition is based on the osmotic phenomenon, based on the difference in the concentration of nutrients in the body of the microbe and the nutrient solution. Thus, water and nutrients dissolved in it enter the microbial cell. As a result of biosynthesis, plastic material of a colloidal structure (proteins, carbohydrates and other substances) accumulates in it, causing the growth and reproduction of the microorganism.

The penetration of nutrients into the cell can be carried out using diffusion and stereochemical specific transfer of nutrients. Each of these processes can occur either actively or passively. With passive diffusion, nutrients penetrate the cell with a fluid current and only when the substance being penetrated is able to dissolve in the cell wall of the bacterial cell. With active diffusion, nutrients penetrate into the bacterial cell undissolved in the cell wall.

During the stereochemical transfer of nutrients (from the external environment into the cell), the role of a carrier is played by permease, a protein component. During this period, nutrients from the environment are actively transported into the cell, carrying out constructive and energy exchanges.

Normally, bacterial cells always have a certain tension in the cytoplasm. This is explained by the fact that the colloids of the cytoplasm, due to the constant flow of water into the cell, are in a swollen state, as a result of which the cytoplasm is tightly pressed to the membrane. This phenomenon is called bacterial cell turgor. Turgor determines the persistence of bacteria. The osmotic pressure in bacteria does not exceed 6x10 Pa. But there are microbes that live in the seas and oceans, whose osmotic pressure reaches about 9x10 Pa.

When bacteria are placed in a solution containing 15-20% sodium chloride or sugar (hypertonic solution), severe dehydration of the bacterial cell occurs and its protoplasmic contents move away from the membrane. This phenomenon is called plasmolysis.

Morphologically, plasmolysis is characterized by the appearance of spherical light-refracting formations in the cell body. In different microorganisms, plasmolysis does not manifest itself to the same extent. Bacillus hay, staphylococci, and sardines are especially resistant to it; Bacteria from the group of Pasteurella, Escherichia, anthrax bacillus, Vibrio cholerae, etc. are easily subject to plasmolysis.

The opposite process to plasmolysis, plasmoptysis, is observed when bacteria are placed in a hypotonic solution of sodium chloride or distilled water. At the same time, water penetrates into the bacterial cell, its cytoplasmic substance swells to its extreme limits, and the cell takes on the shape of a ball. Plasmoptysus, like plasmolysis, entails the death of the bacterial cell.

Types of microbial nutrition. A distinction is made between carbon and nitrogen nutrition of microorganisms. Based on the type of carbon nutrition, microbes are usually divided into autotrophs and heterotrophs.

Autotrophs, or prototrophs, (Greek autos - itself, trophe - food) are microorganisms capable of absorbing carbon from carbonic acid (CO2) in the air. These include nitrifying bacteria, iron bacteria, sulfur bacteria, etc. Autotrophs convert absorbed carbon dioxide into complex organic compounds by chemosynthesis, that is, by oxidizing chemical compounds (ammonia, nitrites, hydrogen sulfide, etc.). Thus, autotrophic microbes have the ability to create organic substances from inorganic ones, such as carbonic acid, ammonia, nitrites, hydrogen sulfide, etc. Since such microbes do not require organic carbon compounds, which are part of animals and humans, they are not pathogenic. However, among autotrophs there are microbes that have the ability to absorb carbon from air CO2 and from organic compounds. Such microbes are defined as mixotrophs (mixo - mixture, i.e. mixed type of nutrition). Certain types of autotrophic microbes carry out nutrition, like green plants, through photosynthesis. Thus, purple sulfur bacteria produce a special chlorophyll-type pigment - bacteriopurpurin, with the help of which light energy is used (photosynthesis) to build the organic substances of their body from carbonic acid and inorganic salts.

Heterotrophs (heteros - other), in contrast to autotrophic microbes, obtain carbon mainly from ready-made organic compounds. Heterotrophs are causative agents of various kinds of fermentations, putrefactive microbes, as well as all pathogenic microorganisms: pathogens of tuberculosis, brucellosis, listrisosis, salmonellosis, pyogenic microorganisms - staphylococci, streptococci, diplococci and a number of other pathogenic pathogens for the animal body.

However, all the physiological diversity of microorganisms does not fit into the narrow concept of autotrophs and heterotrophs. In reality, when environmental conditions (for example, nutrition) change, the metabolism of microbes can change. If a microbe is placed in a different, unusual nutrient medium, it will begin to produce adaptive enzymes. As an example, we can point to nitrogen-fixing bacteria (autotrophs), which, on rich protein nutrient media, stop using molecular nitrogen from the air and begin to assimilate fixed nitrogen (heterotrophic type of nitrogen assimilation).

Heterotrophs most often use carbohydrates, alcohols, and various organic acids as a carbon source. The most complete sources of carbon for feeding these microbes are sugars (especially hexoses), polyhydric alcohols (glycerol, mannitol, sorbitol, etc.), as well as carboxylic acids (for example, glucuronic acid) and hydroxy acids (lactic, malic, etc.). All these carbon sources are usually included in artificial nutrient media for growing microorganisms.

According to the method of assimilation of nitrogenous substances, microbes are divided into four groups:

1) proteolytic, capable of breaking down native proteins, peptides and amino acids;

2) deaminating, capable of decomposing only individual amino acids, but not protein substances;

3) nitrite-nitrate, assimilating oxidized forms of nitrogen;

4) nitrogen-fixing, having the ability to feed on atmospheric nitrogen.

Peptones are used as a universal source of nitrogen and carbon in nutrient media for pathogenic microbes. The need of microorganisms for ash elements is insignificant. The mineral salts (sulfur, phosphorus, etc.) necessary for their life are almost always available in the natural nutrient medium. Sulfur is taken up by bacteria mainly from sulfates or organic amino acid compounds (cystine, cysteine). Sulfur bacteria, for example, can themselves assimilate even the molecular environment. Their body contains up to 80% sulfur. Phosphorus is part of the nucleoproteins and phospholipids of the bacterial cell and plays a very important role in its biosynthetic processes. The source of phosphorus nutrition is various phosphate salts, for example trisodium phosphate (NasPO4).

Microorganisms obtain vital elements - potassium, magnesium and iron - from various salts. Iron is part of hemin (a special organic group in the cytoplasm) and serves as a catalyst for oxidative reactions. Potassium is an essential element in the nutrient medium, but its physiological significance has not yet been fully elucidated. The role of calcium in the life of bacteria (with the exception of bacteria involved in nitrogen fixation from the air) is apparently small. Magnesium activates various bacterial enzymes, in particular protease. Microelements boron, zinc, manganese, cobalt, etc. are found in bacteria in minute quantities and serve as stimulators of microbial growth.

Microbial growth factors. In 1901, Vildier found a special substance in yeast, which he called “bios” - growth substance. In 1904, our compatriot Nikitinsky installed the same growth stimulants in mold cultures. Subsequently, similar substances were identified in pathogenic microorganisms and protozoa. At the same time, it was found that in a number of microbes, under the influence of negligible amounts of growth substances, the accumulation of microbial mass increases and the metabolism changes. The latest data have shown that in terms of their chemical structure and physiological action, stimulants are genuine vitamins or vitamin-like substances.

All studied bacteria require vitamins or growth substances, which mainly play the role of catalysts (accelerators) of the biochemical processes of the bacterial cell. They are also structural units in the formation of certain enzymes. What vitamins do microbes need? Vitamins necessary for the development of microbes include biotype (vitamin H), B vitamins: vitamin B1 (thiamine), B2 (riboflavin), B3 (pantothenic acid), B4 (choline), B5 (nicotinamide), Bb (pyridoxine) , B7 (hemin), - vitamin K, etc.

The concentration of vitamins in the nutrient medium is expressed in micrograms (mcg), the need for them ranges from 0.05-40 mcg/ml. Excess vitamins inhibit the growth of bacteria.

In addition to vitamins, bacterial growth factors include purine and pyrimidine bases and their derivatives (adenine, guanine, cytosine, thymine, uracil, xanthine and hypoxanthine). For example, for hemolytic streptococcus the growth factor is adenine, for Staphylococcus aureus - uracil, the causative agent of tetanus - adenine or hypoxanthine.

Some microorganisms use amino acids as growth factors, synthesized by the microbial cell itself or found in the medium in ready-made form.

Microbial respiration is a biological process accompanied by the oxidation or reduction of various, mainly organic, compounds with the subsequent release of energy in the form of adenosine triphosphoric acid (ATP), necessary for microbes for physiological needs.

The process in which atoms or molecules lose electrons (e~) is called oxidation, and the reverse process, the gain of electrons, is called reduction. This process can be demonstrated by the example of the conversion of partially oxidized ferrous iron into fully oxidized ferric iron and back according to the scheme

Electron transfer is always accompanied by the release of energy, which is immediately utilized by the cell with the help of adenosine diphosphate (ADP) and adenosine triphosphate (ATP). Here it accumulates and is consumed as needed by the microbial cell for its needs.

Hydrogen carriers in biological oxidation and reduction reactions are mainly two pyridine nucleotides (coenzymes of anaerobic dehydrogenases) - nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). Taking hydrogen from the oxidized substrate, they pass into the reducing form (NAD*Hg and NADP#Hg) and transfer hydrogen to another acceptor. NAD*H2 transfers hydrogen mainly to intermediate fermentation products or to the respiratory chain, and NADP'H2 is involved primarily in the biosynthesis reactions of various substances that are part of the microorganism cell.

Types of biological oxidation. From a biochemical point of view, the oxidation of a biological substrate by microorganisms can be achieved by the type of direct oxidation and indirect oxidation, or dehydrogenation.

Direct oxidation is carried out using oxidases by direct oxidation of a substance with atmospheric oxygen or by dehydrogenation - the removal of hydrogen, or more precisely, its electron, from the substrate. Direct oxidation is recorded in most saprophytic microorganisms. For example, Bact. raetanicum, by oxidizing methane, receives energy according to the following scheme:

CH4 + 2O2 - CO2 + 2H2O + 946 kJ energy.

In some microbes that absorb oxygen, oxidation reactions do not reach the final product, i.e. until carbon dioxide is formed. An example of such an incomplete oxidative process is the respiration of acetic acid bacteria, in which the final product of ethyl alcohol oxidation is not carbon dioxide, but acetic acid:

CH3CH2OH + O2 - CH3СООН + Н2О.

Indirect oxidation by dehydrogenation is accompanied by the simultaneous transfer of two electrons, and two protons (H) are removed from the substrate. When enzymatic hydrogen is removed from the substrate using dehydrogenases, two electrons (energy) are released, similar to the formation of acetaldehyde from ethyl alcohol.

There are several dehydrogenases in bacteria, they are named after the hydrogen donor (for example, alcohol dehydrogenase, lactate dehydrogenase), but most of them transfer hydrogen to one of two coenzymes - nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP+). Both coenzymes are easily separated from one dehydrogenase and bind to another dehydrogenase, transferring hydrogen to another acceptor. NADH(+H) transfers hydrogen mainly to fermentation precursors or to the respiratory chain; NADPH (+H+) is mainly involved in biosynthesis.

Aerobic dehydrogenation occurs in the presence of oxygen, and in microbes such as bacilli, the hydrogen acceptor is oxygen, resulting in the formation of water or hydrogen peroxide, depending on the set of enzymes. For this purpose, aerobic bacteria have cytochrome oxidase and a system of hemin enzymes-cytochromes. Obligate anaerobes do not contain catalase, which partly explains the toxicity of oxygen to them.

Anaerobic dehydrogenation occurs in the absence of molecular oxygen. Hydrogen acceptors in this case are other inorganic elements, for example, salts of nitric, sulfuric acids, carbon dioxide, which are converted into more reduced compounds (ammonia, methane, hydrogen sulfide).

The property of anaerobes to transfer electrons to nitrates, sulfates and carbonates ensures sufficiently complete oxidation of organic or inorganic matter without the use of molecular oxygen and makes it possible for them to obtain more energy than during the fermentation process. With anaerobic respiration, the energy output is only 10% lower than with aerobic respiration. Microorganisms characterized by anaerobic respiration have a set of electron transport chain enzymes, but cytochrome oxidase is replaced by nitrate reductase (in the case of using nitrates) or adenylyl sulfate reductase (in the case of using sulfates).

Classification of microbes by type of respiration. In 1861, L. Pasteur, while studying the fermentation properties of microorganisms, discovered that individual microbes are able to reproduce without access to atmospheric oxygen. Bacteria and fungi that use oxygen from the air are called obligate aerobes, and in the absence of oxygen - anaerobes. For aerobes, the final electron acceptor is molecular oxygen; for anaerobes, the final electron acceptor is inorganic compounds such as nitrates, sulfates, and carbonates.

Based on the type of respiration, microorganisms are classified into four main groups.

Obligate (unconditional) aerobes grow with free access of oxygen and have enzymes that allow the transfer of hydrogen from the oxidized substrate to the final acceptor—air oxygen. These include acetic acid bacteria, pathogens of tuberculosis, anthrax and many others.

Microaerophilic bacteria develop at low (up to 1%) oxygen concentrations in the surrounding atmosphere. Such conditions are favorable for actinomycetes, Leptospira, and Brucella.

Facultative anaerobes vegetate both with access to oxygen and in the absence of it. They have two sets of enzymes, respectively. This is a large group of microorganisms, which includes, in particular, enterobacteria, the causative agent of erysipelas in pigs.

Obligate (unconditional) anaerobes develop in the complete absence of oxygen in the environment. Anaerobic conditions are necessary for butyric acid bacteria, the causative agents of tetanus, botulism, gas gangrene, emphysematous carbuncle, and necrobacteriosis.

Redox potential of the nutrient medium. When preparing nutrient media, not only the pH of the medium is taken into account, but also the ratio of substances that donate and accept electrons. The value of the redox potential is denoted by the symbol gHg - the negative logarithm of the partial pressure of hydrogen gas. It is measured with a potentiometer or on a universal ionometer in mV and is indicated in units. The range of rH2 from 0 to 42.6 characterizes all degrees of saturation of the solution with H and O2. Thus, strict anaerobes grow at a low redox potential - from 0 to 12, facultative microorganisms - 0 to 20 and aerobes - from 14 to 35. Therefore, it is minimal when the environment is saturated with hydrogen and maximum when saturated with oxygen. By regulating the degree of redox potential, we create favorable conditions for the growth and reproduction of microorganisms.

Methods for creating anaerobiosis. To isolate anaerobic pathogens of infectious diseases, anaerobic cultivation conditions are created. There are several methods for this.

1. Physical method. It consists of removing air from a desiccator or anaerostat using an oil air pump. Before seeding, liquid media are boiled to remove air from them, i.e., the so-called media regeneration is carried out; To prevent contact of the liquid medium with air, a layer of Vaseline or paraffin oil is applied to its surface.

2. Chemical method. It is based on the use of oxygen absorbers, for example, pyrogallol with sodium hydroxide, potassium or sodium hydrosulfite with sodium bicarbonate in a 1:1 ratio.

3. Biological method (Fortner method). Based on the cultivation of anaerobes in the presence of aerobes (for example, the “miracle stick”) in one Petri dish. First, an aerobic culture grows, and then, as the latter absorbs oxygen from the cup, an anaerobic culture begins to develop.

4. Combined method. Involves the use of the other two, say, physiological and chemical.

It is often possible to weaken or completely neutralize the harmful effect of oxygen on bacteria by adding reducing agents (ascorbic acid, thioglycolate, cysteine) to the medium.

The life of the human body is a very complex and unique phenomenon, however, it has mechanisms that support its existence and at the same time they can be parsed down to the simplest components that are accessible to everyone. Here, first of all, it is necessary to say 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 familiarize yourself in detail with the metabolic process of microorganisms. The processes being studied help to develop new forms of treatment for a wide variety of ailments.

If we talk about the general picture of the metabolic bacterial process, then we are talking about a certain reaction cycle, and some reactions have the task of 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 the general type. It is bacteria that are the basis of the supporting mechanism of the life process of living cells.

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

Catabolism destructive type or destructive reaction. This type of metabolism can be provided by oxidative respiration. The fact is that when the respiratory process occurs, 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. This energy is available in cells in the form of phosphate type bonds.
Anabolism constructive type or reaction of a creative nature. We are talking about the process of biosynthesis that organic molecules undergo; they are necessary in order for life to be maintained in the cell. The whole process takes place as reactions of the chemical type; substances and products of the intracellular type take part in such reactions. Such reactions gain energy by consuming the energy reserve that is stored in ATP.

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

The metabolism of microorganisms relates to the substrate; here we are talking about several stages:

peripheral stage when the substrate is treated with enzymes produced by bacteria;
intermediate stage when intermediate products begin to be synthesized in the cell;
final stage- it begins the process of releasing 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 are capable of accelerating reactions in the cellular structure:

First of all, we must say 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.
Separately, we talk about endoenzymes, which are also protein-type molecules that act inside the cell, and then begin a joint reaction with substrate molecules that come from outside.

It should be noted that there are a number of enzymes that can be produced by the cellular structure on an ongoing basis (constitutive), and there are also those that produce in response to when a certain substrate appears.

Energy type metabolism

This process in bacteria is carried out in certain biological ways:

The first path is chemotrophic, when energy is obtained during chemical reactions.
The second path is phototrophic (here we are talking about the energy of photosynthesis).

If we talk about how bacteria respire in a chemotrophic manner, there can be 3 ways:

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

Features of bacterial metabolism

Such processes are characterized by extreme speed and intensity. In just one day, one bacterium is capable of processing an amount of nutrients that exceeds its own weight by 40 times!
Bacteria adapt to all external conditions, even the most unfavorable ones, very quickly.
As for the nutritional process, it occurs through the entire cell surface. It is noteworthy that there is no way for prokaryotes to ingest nutrients; they are not able to be digested inside the cellular structure; their breakdown occurs outside the cell; chemosynthesis of cyanobacteria is also observed.

How 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 reproduce in such a way that binary fission simply occurs, but this method is far from the only one; budding also happens. If the bacteria have a gram-positive form, then there is the formation of a septum from a cell-type wall and a cytoplasmic-type membrane, which is capable of growing inside. If the bacteria are gram-negative, then a constriction begins to form, after which the cell splits into a pair of individuals.

The speed of the reproduction process is noteworthy; it can be different. If we talk about the vast majority of bacteria, they divide every half hour. And there are tuberculous mycobacteria, the process of division of which is slower; suffice it to say that one division 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 you inoculate bacteria in a liquid nutrient medium, taking a certain volume, and then take a sample every hour, then bacterial growth takes the form of a curved line.

Such substances grow in several phases:

the latent type phase, in which bacteria have the ability to quickly adapt to the nutritional environment, and as for their number, it does not increase;
logarithmic growth phase, when the bacterial number begins to increase exponentially;
the growth phase of the stationary type, when as many new substances appear as they die, and living microorganisms remain constant, all this can reach a maximum level. The term used here is M-concentration; 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 that 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 be involved. The individual characteristics of the human body are of great importance. As for such a process as the regulation of metabolism, it began to be studied in prokaryotes, and specifically in prokaryotes (these are the operons of the intestinal bacillus).

Today, there are a variety of study 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, which have the unique ability to oxidize divalent iron, deserve special attention.

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.

Below is a generalized schematic diagram of the biosynthesis of complex organic compounds, where the following main stages are highlighted: the formation of organic precursors (I) from the simplest inorganic substances, from which “building blocks” (II) are synthesized at the next stage. Subsequently, the building blocks, bonding with each other by covalent bonds, form biopolymers (III): Applications (Fig. No. 3)

The presented scheme of biosynthetic processes does not reflect the complexity of converting low molecular weight precursors into building blocks with high molecular weight. In fact, synthesis proceeds as a series of sequential reactions with the formation of a variety of 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, while 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 included in 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” - self, “trophe” - food) use carbon dioxide as the only carbon source and synthesize all the necessary biopolymers from this simple inorganic precursor compound. The ability for biosynthesis in autotrophs is the highest.

Heterotrophs (from the Greek “heteros” - other) need organic sources of carbon. Their nutritional needs are extremely varied. Some of them feed on 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 they use 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.

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

Many microorganisms 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 with water and organic nutrients. Sources of ash elements (P, S, K, Mg, Fe) are the corresponding mineral salts. The need for these elements is small, but their 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.

Methods of obtaining food, i.e., methods of feeding microorganisms, are very diverse. There are three main methods of nutrition: holophytic, saprozoic, holozoic.

Holophytic nutrition (from the Greek “holo” - whole, “fit” - plant) occurs according to the type of plant photosynthesis. Such nutrition is characteristic only of 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 capturing it. For example, uncolored flagellated and ciliated 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 with their perioral cilia in the form of a funnel, directed with the narrow end into the mouth. Food particles settle at the bottom of the funnel and are swallowed by ciliates. Such ciliates are called sedimentators. Amoebas feed by phagocytosis.

Microorganisms with a holozoic method of nutrition for constructive metabolism use mainly 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 involves the hydrolytic breakdown of complex organic substances into simpler compounds. In this case, carbohydrates are hydrolyzed to simple sugars, proteins to amino acids, and the hydrolysis of lipids produces glycerol and higher fatty acids. Digestive products are absorbed into the cytoplasm and undergo further transformation.

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

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

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

The cytoplasmic membrane is capable of allowing some compounds to pass through and retaining others.

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

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

In saturating a cell with nutrients, simple diffusion is not of great importance. However, this is precisely 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, so the cells of microorganisms have a fairly high osmotic pressure. Its value in many microbes reaches 0.5-0.8 MPa. In the environment, 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 transport enzymes called permeases. They seem to capture molecules of dissolved substances and transfer them to the inner surface of the membrane.

Simple and facilitated diffusion are options for 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 the concentration gradient. In this case, energy is expended on such transfer and the transfer is called active. Active transfer occurs with the participation of specific proteins, is associated with the energy metabolism of the cell and allows the accumulation of nutrients in the cell in a concentration many times higher than their concentration in the external environment. Active transport is the main mechanism for the supply of nutrients into cells with saprozoic nutrition.

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55. Metabolism of bacteria. Chemosynthesis. Aerobic and anaerobic bacteria. Complete and incomplete oxidation. Anaerobic respiration.

Metabolism is a set of various enzymatic reactions occurring in a microbial cell and aimed at obtaining energy and converting simple chemical compounds into more complex ones. Metabolism ensures the reproduction of all cellular material, including two unified and at the same time opposite processes - constructive and energy metabolism.

Metabolism occurs in three stages:

1. catabolism - the breakdown of organic substances into simpler fragments;

2. amphibolism - intermediate exchange reactions, as a result of which simple substances are converted into a number of organic acids, phosphorus esters, etc.;

3.anabolism - the stage of synthesis of monomers and polymers in the cell.

Metabolic pathways have been formed through the process of evolution.

The main property of bacterial metabolism is plasticity and high intensity, due to the small size of organisms.

Metabolic pathways in prokaryotes include fermentation, photosynthesis and chemosynthesis.

Chemosynthesis is a method of nutrition in which the source of energy for the synthesis of organic substances is the oxidation processes of various inorganic and inorganic substances. Chemosynthesis is often compared to respiration; in microorganisms, respiration can be aerobic or anaerobic.

Anaerobic respiration is an energy-producing cellular process in which the final electron acceptor is an oxidized organic or inorganic substance other than oxygen.

Anaerobic respiration is associated with the functioning of the electron transport chain and is a transitional link from substrate phosphorylation to aerobic respiration in the evolution of energy processes in the cells of living organisms.

Electron acceptor	Refurbished Product	Process	Microorganisms that carry out this process
		“Nitrate breathing” - dissimilatory nitrate reduction	Bacteria family Enterobacteriaceae, kind Bifidobacteriaceae
		"Nitrate respiration" - denitrification	Pseudomonas, Bacillus
		“Carbonate respiration” – methanogenesis	Methanogenic archaea
		“Carbonate respiration” – acetogenesis	Homoacetogenic bacteria (Clostridium, Sporomusa, Acetobacterium, Peptostreptococcus, Eubacterium)
		"Iron Breath"	Geobacter
2 + fumarate	Succinate	"Fumarate Breath"	Enterobacteriaceae, vibrios and propionic bacteria

Most aerobic organisms oxidize nutrients during respiration to carbon dioxide and water.

Since the highest degree of oxidation of carbon is achieved in the CO2 molecule, the process is called complete oxidation.

With incomplete oxidation, partially oxidized organic compounds, such as acetic, fumaric, citric, malic, and lactic acids, are released as metabolic products. The substrate in this case is carbohydrates and organic alcohols.

Complete oxidation can occur using the tricarboxylic acid cycle with the participation of nicotinamide dinucleotide, flavinamide dinucleotide and acetylation coenzyme dehydrogenases

This metabolic pathway not only leads to complete oxidation of nutrients, but plays a significant role in biosynthetic processes. As a result of the entry of protons into the ATP-regenerating system of the respiratory chain, ATP synthesis is activated and ATP is formed to provide the cell with energy. In the respiratory chain, the main role is played by enzymes - cytochromes, flavoproteins and iron-sulfur proteins. During the respiration of aerobic microorganisms, pyruvic acid undergoes complete oxidation to CO2 and H2O, entering a complex cycle of transformations (Krebs cycle) with the formation of tri- and dicarboxylic acids, which are successively oxidized (H2 is eliminated) and decarboxylated (CO2 is eliminated).

Respiratory chain or electron transport system in prokaryotes it is located on the cytoplasmic membrane (in eukaryotes - in the inner membrane of mitochondria). The main function of this system is to pump protons, which is why it is often called a “proton pump.”

Protons are transported across the membrane in such a way that an electrochemical gradient is created between the inner and outer sides of the membrane with a positive potential on the outside and a negative potential on the inside. This charge differential occurs due to the specific arrangement of the components of the respiratory chain in the membrane and serves as the driving force for the process of ATP regeneration (or other processes requiring energy input).

The hydrogen of the reduced NAD2H is transferred to the coenzyme (FAD) of the flavin enzyme, which is reduced to FAD2H. From the reduced flavin dehydrogenase, hydrogen is transferred to the cytochrome of the cytochrome system, and the hydrogen atom is split into a hydrogen ion and an electron. Cytochrome is converted from an oxidized form to a reduced form. The reduced cytochrome transfers electrons to the next cytochrome, etc.

Cytochromes are alternately reduced and oxidized, which is associated with a change in the valence of iron contained in their prosthetic group. The last cytochrome transfers electrons to cytochrome oxidase, restoring its coenzyme. The final reaction is the oxidation of reduced cytochrome oxidase by an oxygen molecule. Oxygen, due to the transfer of electrons to it (from cytochrome oxidase), is activated and acquires the ability to combine with hydrogen ions, resulting in the formation of water. This is where complete oxidation of the original organic matter ends for aerobes.

The energy released during the transfer of electrons in the respiratory chain is spent on the synthesis of ATP from ADP and inorganic phosphate under the influence of ATP synthetase, which is localized on the membrane. This synthesis of ATP due to the energy of electron transport across the membrane is called oxidative phosphorylation.

The following three areas are particularly important in the breathing mechanism:

*components of the respiratory chain;

*their redox potentials;

*their relative position in the membrane.

The components of the respiratory chain are enzymatic proteins with relatively tightly bound low molecular weight prosthetic groups, immersed in a lipid bilayer. The most important of them are flavoproteins, iron-sulfur proteins, quinones and cytochromes.

Flavoproteins are enzymes containing FAD as prosthetic groups and act as hydrogen carriers.

Iron-sulfur proteins are redox electron transfer systems. They contain iron atoms bonded to cysteine sulfur and to inorganic sulfide sulfur. Thus, Fe-S centers are prosthetic groups of proteins. Iron-sulfur proteins are also involved in the process of nitrogen fixation. Some proteins have names related to their origin or function: ferredoxin, putidaredoxin, rubredoxin, adrenodoxin.

Quinones are lipophilic compounds localized in the lipid phase of the membrane and are capable of transferring hydrogen and electrons. They are usually contained in excess in the membrane and are sometimes hydrogen collectors, receiving it from coenzymes and transferring it to cytochromes. Gram-negative bacteria contain ubiquinone (coenzyme Q), gram-positive bacteria contain naphthoquinones, and plant chloroplasts contain plastoquinones.

Cytochromes are systems that transport only electrons; they do not transport hydrogen. Cytochrome contains heme as a prosthetic group. The central iron atom of the heme ring participates in electron transfer, changing its valence. Cytochromes are colored and differ in types a, a3, b, c, o, etc.

Redox potential is a quantitative measure of the ability of certain compounds or elements to donate electrons. A hydrogen half-cell - a platinized or platinum electrode, immersed in an acid solution and flowing around gaseous H2 at a pressure of 1.012 bar and pH 0, has a potential of zero.

This value is E0. E` is the measured potential of the redox system; its value is the more negative, the lower the ratio of the concentration of the oxidized form to the concentration of the reduced form.

Several groups of bacteria have a unique ability for bioluminescence. Luminous bacteria include gram-negative rod-shaped marine bacteria, chemoorganotrophic, halophilic, psychrophilic, facultative anaerobic, free-living or symbiotic, for example Photobacterium rhosphoreum and P. leiognathi, living in the luminous organs of fish.

Under aerobic conditions, microorganisms carry out the process of aerobic respiration and luminescence.

They have a normal respiratory chain and operate the Krebs cycle.

The luminescence depends on the oxidation of a long-chain aldehyde with 13–18 carbon atoms per molecule.

The excited flavin glows under the action of luciferase, a two-subunit enzyme like monooxygenase. Bacteria of the genera Photobacterium, Beneckia, Vibrio, Photorhabdus are capable of luminescence.

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Introduction

1. General concepts about metabolism and energy

2. Constructive metabolism

3.1 Carbon sources

4. Types of microorganism metabolism

7. Energy metabolism of chemoorganotrophs using the respiration process

8. Energy metabolism of chemolithoautotrophs

Conclusion

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

The set of 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 reproduce themselves and their close relationship with the environment. Any organism can exist only under the condition of a constant flow of nutrients from the external environment and the release of waste products into it.

Nutrients absorbed by the cell are converted into specific cellular components as a result of complex biochemical reactions. The set 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 occur with the absorption of energy. The energy required for the biosynthesis processes of other cellular functions, such as movement, osmoregulation, etc., is obtained by the cell through the flow of oxidative reactions, the totality of which represents energy metabolism, or catabolism (Fig. 1).

All living organisms can only use chemically bound energy. Each substance has a certain amount of potential energy. The main material carriers of its chemical bonds, the rupture or transformation of which leads to the release of energy.

The energy level of chemical bonds is not the same. For some, it has a value of about 8-10 kJ. Such connections are called normal. Other bonds contain significantly more energy - 25-40 kJ. These are the so-called macroergic connections. Almost all known compounds that have such bonds include phosphorus and sulfur atoms involved in the formation of these bonds.

Adenosine triphosphoric acid (ATP) plays a vital 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 results in the release of a significant amount of free energy:

ATP + H20→ADP + H3P04 - 30.56 kJ

Hydrolysis occurs with the participation of specific enzymes, providing energy to biochemical processes that involve energy absorption. In this case, ATP plays the role of 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 the reactions of addition of a phosphoric acid residue to the adenosine diphosphoric acid (ADP) molecule:

ADP + H3P04 → ATP + H20

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

1) use of light energy;

2) use of energy from 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, forming a single whole, since the products of energy metabolism (ATP and some low-molecular compounds) are directly used in the constructive metabolism of the cell (Fig. 6.1).

In microbial cells, the relationship between energetic and constructive processes depends on a number of specific conditions, in particular on the nature of the nutrients. Nevertheless, catabolic reactions usually exceed 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 completely depends on the amount of available energy obtained during energy metabolism.