Until recently, it was a mystery how termites managed to live (and even thrive) on wood alone. It was known that the decomposition of the cellulose consumed by them is carried out by bacteria - intracellular symbionts of protozoa, which in turn live in the intestines of the termite. But cellulose is a low-nutrient substrate; in addition, it cannot serve as a source of nitrogen, which termites need in much greater quantities than is contained in plant tissues. However, a striking conclusion was recently reached by a group of Japanese researchers who began studying the composition of the genome of symbiotic bacteria of flagellates. Along with the genes responsible for the synthesis of cellulase, an enzyme that destroys cellulose molecules, the genome contains genes encoding enzymes responsible for nitrogen fixation - binding free atmospheric nitrogen N2 and converting it into a form suitable for use not only by bacteria themselves, but also by flagellates and termites.

People who are far from biology sometimes confuse termites with ants, since both lead a colonial lifestyle, erect large buildings (termite mounds and anthills), and in addition, are characterized by the division of labor between separate groups of individuals: they have workers, soldiers, as well as females (queens) and males producing offspring.

However, the similarity between ants and termites is purely external, explained by the social way of life that arose in both groups. In fact, these insects belong to different, far from related, orders. Ants are hymenoptera, relatives of wasps and bees. Termites form a special order, and, unlike Hymenoptera, they are insects with incomplete transformation (they do not have a pupa, and the larva, through a series of successive molts, gradually becomes more and more similar to an adult insect).

Termites are not found in temperate, much less northern, latitudes, but they are extremely numerous in the tropics, where they are the main consumers of plant debris. Unlike many other animals, termites can feed on wood alone - more precisely, fiber (cellulose), which they process extremely quickly. Any wooden structure erected in the tropics is susceptible to the destructive activity of termites. A house that does not have special protection can be literally eaten by termites within a few years.

Researchers have long been interested in the question: how do termites cope with the decomposition of fiber (after all, this has always been considered the prerogative of bacteria and fungi!) and how can they even get by with such low-nutrient food? For a long time it was believed that protozoa, representatives of a special group of flagellates that live in the intestines of termites, help termites in processing fiber. But later it turned out that flagellates themselves need the help of endosymbionts - bacteria living in their cells (endosymbiont means “living in a cell”), which produce cellulase, an enzyme that decomposes cellulose.

Thus, this entire symbiotic system is structured according to the matryoshka principle: flagellates live in the intestines of the termite, and bacteria live inside the flagellates. Termites find food (plant debris or wooden structures), grind the wood mass and bring it to a fine state in which flagellates can absorb it. Then the bacteria living inside the flagellate get down to business, carrying out the basic chemical reactions to process the initially inedible product into a completely digestible form.

However, much about this system remained unclear. For example, it was unknown where termites get the nitrogen they need (and its relative content in the bodies of animals, including termites, is significantly higher than in plant tissues). However, recent research by Japanese scientists has answered this question.

The object of research by Yuichi Hongoh and his colleagues from the RIKEN Advanced Science Institute, Saitama and other scientific institutions in Japan was the symbiotic system of the termite that is widespread in Japan Coptotermes formosanus. This species, leading an underground lifestyle, is known as a malicious pest, causing enormous damage to wooden structures, not only in its homeland, in Southeast Asia, but also in America, where it was accidentally introduced. To fight with Coptotermes formosanus In Japan, several hundred million dollars are spent annually, and in the United States - about a billion.

Flagellates living in the hind intestine of termites Pseudotrichonympha grassii belong to a genus whose representatives are often found in various termites leading an underground lifestyle. Each flagellate is constantly inhabited by about 100 thousand bacteria belonging to the order Bacteroidales and having the code name “phylotype CfPt1-2”.

During the work, flagellates were removed from the termite intestines, the membranes of their cells were destroyed, and 10 3 -10 4 cells of endosymbiotic bacteria were released from each. The resulting mass of bacteria was subjected to amplification (increasing the number of copies of DNA molecules present there), after which a search for certain gene sequences was carried out. In the circular chromosome containing 1,114,206 base pairs, 758 putative protein-coding sequences, 38 transfer RNA genes and 4 ribosomal RNA genes were identified. The discovered set of genes made it possible to reconstruct in general terms the entire metabolic system of the endosymbiotic bacterium.

The most striking thing was the discovery of genes responsible for the synthesis of those enzymes that are necessary for nitrogen fixation - the process of binding atmospheric N 2 and converting it into a form convenient for use by the body. In particular, genes were found that are responsible for the synthesis of nitrogenase, the most important enzyme that cleaves the strong triple bond in the N2 molecule, as well as genes encoding other proteins necessary for nitrogen fixation.

The authors of the work under discussion note that, in fact, the ability of termites to fix nitrogen had already been discovered earlier, but it was unclear which symbiotic organisms were responsible for it. The identification of genes responsible for nitrogen fixation in the studied endosymbiotic bacteria was unexpected, since nitrogen fixation had never been observed in bacteria of this group (Bacteriodales) before. In addition to binding N2 and converting it into NH3, the studied bacteria are apparently capable of utilizing those products of nitrogen metabolism that are formed during the metabolism of the protozoa themselves. This is an important point, since the binding of N2 requires large energy costs, and if there is enough nitrogen in the termite food, then the intensity of nitrogen fixation can be reduced.

In this publication you will find the most complete information on hirudotherapy - one of the most ancient and highly effective methods of natural therapy. Here you can find information about the anatomy and mechanisms of the therapeutic action of the leech; the methods of leech attachments in practical medicine are described, indications and contraindications for hirudotherapy are formulated. The manual is well illustrated, contains a list of literature recommended for doctors for independent work, and a self-control section, which includes a large number of test questions.

It has been published since 2006 and is the first officially approved textbook on hirudotherapy for the postgraduate education system of doctors.

Intended for doctors of various specialties who are interested in hirudotherapy, mastering hirudotherapy and involved in the therapeutic use of leeches, as well as for senior students of medical universities and readers of specialized literature in the health field.

Book:

2.3. Symbiotic bacteria. Role in the physiology of medicinal leeches

When considering the biology of medicinal leeches, it is necessary to dwell in more detail on the problem, which is usually rather briefly and incompletely reflected in the literature. We are talking about microorganisms (microflora) found in the stomach intestines of medicinal leeches. Later we will touch on this issue from a clinical perspective, because its underestimation, and sometimes even basic ignorance, can lead to serious complications during treatment. Moreover, this problem is completely ignored during training in various courses on hirudotherapy. Apparently, this is due to the lack of awareness of teachers and the complacency of specialists due to the “bactericidal effect of medicinal leeches” widely declared in the domestic literature.

The fact is that the gastrointestinal tract of medicinal leeches, as well as other types of leeches, is not sterile. It is populated by microorganisms. Moreover, Hirudo medicinalis As a rule, one type of bacteria is determined, and not associations of microorganisms characteristic of other leeches. This type of bacteria has long attracted the attention of researchers. In 1946, M. B. Golkin (hereinafter cited from: Khomyakova T. I. et al., 1998) the bacterium was isolated and morphologically described as a mobile rod thickened in the middle measuring 0.6 by 2.5–4.5 µm, containing 2–3 granular inclusions that disappear during cultivation on nutrient media, and is called “Leech bacterium”. H. Busing and co-authors (1953) identified it as an independent species, which they called “Leech bacterium” - Bacilus hirudinis. Subsequently it turned out that in fact Bacilus hirudinis is Aeromonas hydrophila. In one of the latest works devoted to the study of the microflora of medicinal leeches, J. Graf (1999) showed with a high degree of reliability (including by comparing certain sections of the genome) that the symbiont bacterium belongs to Aeromonas veronii biovar sobria. It should be noted, however, that the author did not study wild (natural) leeches, as in most previous studies, but farmed ones in Germany (Noyer Apotheke) and England (Biopharm), and his conclusions require some clarification. However, according to D. R. Mackay et al. (1999), most of the leeches they studied contain A. sobria.

What does it represent Aeromonas? The following is the data of T.I. Khomyakova and co-authors (1998), summarized by them in a review devoted to the symbiont bacterium: “ Aeromonas– gram-negative rods, facultative anaerobes. Found in fresh and waste waters, some species are pathogenic to fish and frogs, causing septicemia in them. In humans they cause diarrhea and bacteremia. With pathogenic properties A. hydrophila There are many publications in both domestic and foreign literature. However, it should be noted that there are many different strains of this bacterium, which differ significantly from each other, including in terms of pathogenicity for humans. Thus, strains isolated from tissues and fluids of patients are somewhat different from strains isolated from the environment. The cell surface properties of different strains and their genomic composition are also different. Even within the same strain, differences in structural and pathogenic properties are possible.”

From the very beginning, scientists were interested in the possible role of this bacterium both in the life of leeches and in their medicinal use. The facts accumulated to date suggest that Aeromonas, which under normal conditions lives in the intestines of the worm, is a symbiont of the leech and is useful for the host’s body. This conclusion is based on a number of observations.

Firstly, back in 1946, the ability of the “Leech bacterium” to synthesize a substance that prevents blood clotting was demonstrated. The assumption about the possible role of the bacterium in maintaining the blood in the leech’s stomach in a liquid state is supported by the fact that later studies of the bacterium discovered an enzyme (metalloproteinase) that converts the g-chain of fibrin dimer into a monomeric form. It can participate in fibrinolysis processes. Research in this direction continues, but to date the degree of participation of bacteria in the process of maintaining the liquid state of the blood remains not fully understood.

Secondly, the bacterium plays a certain role in the digestive processes of leeches. If the anatomical structure of the gastrointestinal tract of leeches is characterized by the presence of clear differentiation of various sections (pharynx, stomach, intestines, rectum), then at the cellular (histological) level the differences in the structure of the lining of various sections of the intestinal tube are insignificant. The absence of cells secreting digestive enzymes was confirmed by the results of biochemical studies. The obvious deficiency of enzymes, which are generally believed to be necessary for the complete digestion of protein, suggested that the “leech bacterium” is involved in the digestive processes. This hypothesis received serious support in the work of H. Busing and co-authors (1953), who showed that the bacterium they isolated from the intestines of a medicinal leech demonstrated in vitro the ability to slowly digest blood. In 1967, J. B. Jennings and V. M. van der Lande published the results of their research on various types of leeches. A study of digestive enzymes revealed the presence of exopeptidases in the complete absence of endopeptidases, lipase and amylase. And having examined the extract isolated from a medicinal leech Aeromonas, the authors discovered enzymes in it that can play a certain role in the host’s digestive processes.

Thirdly, it has been suggested (Khomyakova T.I., Khomyakov Yu.N.) that microflora may participate in providing the leech with some nutrients necessary for its life (peculiar leech vitamins).

Fourthly, analysis of the available literature data allows us to conclude about the important role Aeromonas to prevent the proliferation of other types of microorganisms, and possibly viruses, that enter the gastrointestinal tract of the leech with the blood of sick animals. This is confirmed by numerous observations that have shown that already in the first hours after a leech feeds, a significant increase in the number of symbiont bacteria occurs in its stomach.

Thus, although the role, extent and nature of participation Aeromonas in various life processes of the medicinal leech require further study, the presented facts undoubtedly allow us to draw a conclusion about its benefits for the leech’s body.

There is a complex system of relationships between the worm and the bacteria that live in its intestines. Thus, specific proteinase inhibitors produced by the glands of the medicinal leech (eglins and bdellins) prevent the rapid proliferation of endosymbionts (Roters F. J., Zebe E., 1992). According to unpublished data by Yu. N. Khomyakov, destabilase of the secretion of the salivary glands of the leech also has a bactericidal effect against Aeromonas action. These data were confirmed in the work of L.L. Zavalova and co-authors (2001).

As already mentioned, the domestic literature on hirudotherapy declares the antimicrobial effect of leeches or individual components of their saliva (Hirudotherapy: A Guide for Doctors / Ed. V. A. Savinov, 2004). This is often interpreted as the presence in the secretions of leeches of substances capable of destroying bacteria that cause pathological processes in the human body. The fallacy of these statements is associated with the mechanical transfer of conclusions from in vitro studies to the body of a medicinal leech and humans. In fact, with those concentrations of enzymes that are present in a living leech (and not its extract), and even more so, given the amount of substances introduced by a leech into human tissue, we should rather be talking about a bacteriostatic effect, and even then only in the tissues directly in the wound area.

Many researchers were interested in: if a leech attacked a sick animal, whether there is a danger of transmitting the infection when the leech is used in the future, and also what happens to microorganisms that enter the leech’s stomach along with the blood it sucks. Similar studies have been undertaken several times. In Russian literature, the work of P. N. Andreev (1923) is most often cited. Let us dwell on it in a little more detail. The purpose of the work was to study the possibility of using leeches as a kind of biological container for a number of pathogenic microorganisms. In this regard, the period of time during which various pathogenic bacteria and protozoa retain viability and virulence inside the body of a leech in cases of their absorption with sucked blood was determined. Before research, leeches were fed on sick animals. Then, after various periods, the viability of microorganisms inside the leech’s body was studied. Blood was obtained by squeezing or applying salt to the leech's body. Typhoid and anthrax bacteria (in two experiments), chicken spirochetes (in five experiments), paratyphoid bacteria, swine septicemia bacteria, tuberculosis, Typus humanus, pearl mussels, trypanosomes Lewisii, Equiperdum, Brucei, as well as fowlpox and swine fever viruses (one experiment for each pathogen). Typhoid bacteria were determined by plating on a nutrient medium. In one experiment they were detected up to 6 days, in another – up to 30. Anthrax bacilli were detected through cultures and vaccinations of animals. They lasted up to 14 and 17 days. For chicken spirochetes, the longest viability period was 3 weeks. Trypanosomes were identified by microscopic examination for up to 9 days. However, pig septicemia bacteria remained viable for up to 22 days, bacilli Typus bovines– up to 60 days, paratyphoid B bacteria – up to 3 months. The author concluded, firstly, that the persistence of protozoa in the body of leeches is less than that of bacteria. This was explained by their lower overall resistance to external adverse factors. Secondly, about the presence of bactericidal properties in the contents of the leech’s intestinal canal. Of course, the small number of experiments, and most importantly, the shortcomings of the method of obtaining the material in the given work, do not make it possible to draw final conclusions about the duration of preservation of various bacteria and protozoa in the leech’s stomach. At the same time, an analysis of the data available in the foreign literature allows us to state that microorganisms “foreign” to a leech can persist for some period and even multiply to some extent without causing significant harm to its “health” (Graf J., 1999).

Investigating the quantitative dynamics of reproduction Escherichia coli, Pseudomonas aeruginosa And Staphylococcus aurens in the gastric intestine after their addition to the blood on which the leeches fed, S. Indergand and J. Graf (2000) showed that in two out of three (in the first experiment) and in two out of four (in the second experiment) animals they studied E. coli was detected after 42 and 162 hours, respectively. Unlike E. coli, P. aeruginosa And St. aurens were able to survive and even multiply in the lumen of the gastric intestine for at least 162 hours, but the increase in their number was 100 times less than under similar conditions outside the leech body. In addition, in vitro experiments showed that, in contrast to the results of previous studies, Aeromonas, isolated from the stomach intestines of medicinal leeches, did not itself have an inhibitory effect on any of the bacteria studied. It was suggested that in vivo, activation of certain genes of the symbiont appears to occur as a result of contact with some cells inside the leech. Moreover, in cases where leeches ingest microorganisms with the blood of sick animals, although they persist, they cannot reproduce fully and also displace the symbiont bacterium. Ultimately, after a certain period of time, the foreign bacteria die, and only the symbiont bacterium remains in the intestine. It should be noted that for the study we took healthy, full-fledged leeches purchased from manufacturing companies in England and Germany, and not wild ones, among which there are a sufficient number of sick and weakened animals.

Thus, an analysis of all currently available literature data, our own observations and studies of the process of reproduction and development of leeches, as well as the results of their clinical use, allow us to draw the following important conclusions.

Due to the peculiarities of obtaining food, the leech is adapted to process the blood of sick animals.

For some period of time after feeding, various bacteria or protozoa may be present in its gastric intestine, which got there with the blood of sick animals. During this same period, the concentration of symbiont bacteria is maximum. They protect the leech’s body from the possible adverse effects of foreign microorganisms. In the case of clinical use, such unfasted leeches can become a source of human infection.

During the process of starvation of leeches, foreign bacteria die or are removed from its body, and the titer Aeromonas is significantly reduced. This is what makes ready-to-use artificially grown leech safe.

Thus, the presence of a long (at least 3–4 months) period of fasting of the animal is the most important condition for the safe use of leeches. In addition, it is extremely important to create for the animal during this period all the conditions necessary for its normal life, selection and destruction of weakened individuals.

It seems more than strange to us that the recommendations of some authors, familiar only with the literature and who have absolutely no knowledge of the issues of breeding leeches, “strengthen the antimicrobial properties of the intestinal canal of leeches by keeping them in water devoid of pathogenic microorganisms,” or carry out “strict microbiological control of the blood for feeding leeches,” and also “test for the presence of blood in the intestinal canal of leeches.” The recommendations “to keep leeches in an antibiotic solution” are even more unfounded (Baskova I.P., Isakhanyan G.S., 2004). There is not a single work proving that a fasted, healthy leech bred in a biofactory would become a source of any infection other than A. hydrophila . But it has also been recorded in isolated cases of leeches being placed on transplants, that is, under conditions in which severe tissue hypoxia is noted and local immunity is sharply suppressed. In our practice, over more than 20 years of treatment (several tens of thousands of patients were treated during this time), provided that healthy animals were used, correct choice of attachment sites and management of the attachment reaction (which will be discussed further), the formation of abscesses at the sites of leech attachment was not observed. once. Recommendations similar to the above, if attempts are made to implement them, can lead to a serious crisis in hirudotherapy.

The word “symbiont” comes from the ancient Greek “living together, cohabitation” and refers to various living organisms that support each other’s existence. The process of close and long-term coexistence of different types of living organisms is called symbiosis. Such relationships between symbionts are successful if they benefit all participants in the process and increase their chances of survival. A striking example is symbiont bacteria living in the human intestine, without which the digestion process, and, consequently, our life would be impossible.

• two animals (a hippopotamus and a bird that brushes his teeth);
• plants and insects (flowers pollinated by only one type of insect);
• microorganisms and plants (nodule bacteria involved in the process of obtaining food from legumes);
• humans and bacteria (microorganisms that live in our intestines help us survive and enjoy life themselves);
• even individual cells with each other (the symbiosis of prenuclear prokaryotic cells gave birth to a full-fledged eukaryotic cell with a clearly defined nucleus, which marked the beginning of the process of evolution on our planet).

And there are also lichens as a result of the symbiosis of a fungus and algae, which survive where neither fungi nor algae can live separately. There is coexistence between the crab and the sea anemone, where the former is a means of transportation and the latter a defensive weapon. And there are countless such examples.

Let's consider two examples of symbiosis of microorganisms with humans and plants - human symbiont bacteria and nodule bacteria involved in the nutrition of legumes.

Macroorganism + microorganism = human

Symbiont bacteria live in our intestines, on mucous membranes, on the skin and constitute the so-called normal microflora. Our native microorganisms:

1. They provide protection to the entire body by killing or depriving “invading” bacteria of food. They do not allow dangerous microbes or viruses coming from outside to settle on the skin or mucous membranes, thereby creating the body’s immune system.
2. Participate in digestion. Bacteria living in the human intestines produce digestive enzymes, without which it is impossible to digest certain types of food.

About 500 species of different bacteria take part in the formation of normal human microflora. Thus, the presence of E. coli in the human body (in certain quantities) is an indispensable condition for the digestion of lactose. In turn, lactobacilli convert the resulting lactose and other carbohydrates into lactic acid, participating in the process of obtaining energy.

Where and how do our little friends live?

Bacteria are found along almost the entire length of the gastrointestinal tract, from the mouth to the rectum. But the most important ones live in the intestines. Here they produce enzymes and vitamins, without which the digestion process is simply impossible.

In each part of the intestine live exactly those microorganisms that are adapted to certain living conditions and nutrient content. For example, in the cecum, the most numerous group is bacteria that break down cellulose, which makes fiber processing possible.

Bacteria in the small intestine have to survive in rather harsh conditions. This is where aggressive substances are found that are fatal to many microorganisms. For example, hydrochloric acid, necessary for digestion, kills a significant number of microbes. Only a few species of bacteria and yeast are able to survive in such an environment.

In addition, it is in the small intestine that the process of absorption of nutrients is in full swing. This means that bacteria have to fight for food with the body itself. In addition, incompletely processed substances, which are not always suitable for feeding bacteria, end up here.

The small intestine is connected to the circulatory and lymphatic systems that transport received nutrients. And the nervous system, based on a signal from the small intestine, regulates the composition and amount of hormones needed by the body. That is, the small intestine, thanks to its symbionts, is an energy station and supplier of nutrients.

In the large intestine, bacteria live much more freely, so their number and species diversity are much greater. The body sends undigested food debris and other waste (fragments down to the size of molecules) into the large intestine for further removal.

Enemies of our friends

Antibiotics are a relatively recent invention of mankind. It is difficult to estimate how many lives were saved thanks to this discovery. However, as you know, you have to pay for everything. Antibiotics destroy all bacteria, without distinguishing between good and bad.

That is why, after taking antibiotics, the intestinal microflora looks very sad. This immediately affects not only our digestion, but also greatly reduces our immunity. That is, it turns out that the danger of contracting the next disease becomes greater after taking medications designed to protect our health.

Scientists are trying to break this vicious circle by developing new, highly targeted drugs. But many years of widespread use of antibiotics have led to the fact that the human microflora is becoming increasingly weaker. And the absence or insufficient number of symbiont bacteria entails a whole bunch of chronic diseases: diabetes, cancer, obesity, etc.

Symbionts in the plant kingdom

Plants, in their desire to survive, also do not hesitate to use symbionts. For example, the well-known lichen is not, in fact, a separate plant. It is a symbiotic system of green algae and fungi.

As you know, algae cannot survive without water, and fungi are not able to synthesize nutrients on their own (they use what other microorganisms have produced). But these shortcomings are mutually destroyed in a symbiotic group. Algae, through photosynthesis, create nutrients for fungi, and in return receive a comfortable living environment: the necessary humidity, soil acidity, and protection from ultraviolet radiation. As a result, lichens manage not only to survive, but to feel very confident in rather harsh conditions, where they have no competitors for a place in the sun.

Another example of symbiosis is orchids, in the root system of which fungi and microorganisms live. In this triple alliance, bacteria are responsible for the close relationship between the host plant and the symbiont fungus. The most amazing thing is that not only fungi and microorganisms cannot exist without a plant, but the orchid also dies if its symbionts are destroyed.

But perhaps the most striking example of a plant symbiotic system is nodule bacteria in alliance with plants of the legume family.

How to grow a good crop of legumes

The air we breathe contains nitrogen (as much as 78% of the total volume). This chemical element is necessarily included in proteins and nucleic acids, which means it is vitally necessary for all living organisms on Earth.

Humans and animals obtain nitrogen through food, mainly from animal and plant proteins. But where do plants get nitrogen from?

Plants cannot obtain nitrogen directly from the atmospheric air on their own. The soil also contains nitrogen, but, firstly, there is very little of it, and secondly, a significant part of it is contained in organic compounds, which plants are not able to absorb.

This is where nitrogen-fixing bacteria come into play. They are able to convert organic compounds containing nitrogen into mineral compounds (nitrates) available for plant nutrition.

A special place among nitrogen-fixing bacteria is occupied by the so-called nodule bacteria. These symbiont microorganisms form nodules on the roots of leguminous plants (clover, lupine, peas, vetch). Nodule bacteria bind free atmospheric nitrogen and deliver it directly to the table of their plant host.

Thus, with the help of symbiont nodules, plants are able to obtain nitrogen, and microorganisms, in turn, take nutrients from plants (products of carbohydrate metabolism and mineral salts) for their own growth and development.

For the successful development of a symbiont system (plant + microorganism), certain conditions are necessary:

• temperature;
• humidity;
• soil reaction;
• strain of bacteria.

Under natural conditions, nodule bacteria of various types are found, and not all of them are quite effective. Therefore, in agriculture, bred strains of microorganisms are used, infecting legume plants with them, which leads to an increase in yield.

However, in the case of legumes, symbiosis is a necessary necessity. If there is enough nitrogen in the soil (for example, nitrogen fertilizers), then nodule bacteria will lose their importance for the host, and their colonies will be destroyed by the plant itself.

So, symbiosis is an important, necessary and sometimes vital thing. Symbiont systems exist in higher animals, plants, fungi, bacteria, algae... In a word, almost everywhere. And we would not have been able to not only survive, but even be born, if nature had not created such a powerful tool for survival as the system of symbionts.

Many non-leguminous plants, both woody and shrubby, and herbaceous, also have root shoots capable of fixing molecular nitrogen. Nitrogen fixation in such cases, as in legumes, is based on symbiosis with prokaryotes. In tree and shrub vegetation, nodules are most often formed by nitrogen-fixing actinomycetes, in herbaceous vegetation - by bacteria. In most cases, the symbionts of trees and shrubs are actinomycetes of the genus Frankia(Fig. 49). These are aerobic organisms with septate mycelium that forms sporangia.

There are 17 known genera of woody and shrubby angiosperms that form Frankia nodules. They belong to the orders Casuarinales, Coriariales, Fagales, Cucurbitales, Myricales, Rhamnales And Rosales. Among the plants that are very efficient at fixing nitrogen are casuarina ( Casuarina), alder ( Alnus), sea ​​buckthorn (Hip-pophae), waxweed is less effective in this regard (Myrica) partridge grass ( Dryas), sucker (Elaeagnus) and shepherdia (Shepherdia).

Root nodules of woody plants are quite large; they usually form on the lateral roots. There are two types of nodules - coral (dense plexuses of roots branched like corals) and with roots growing through the lobes of the nodule (loose bundle of thickened roots) directed

Rice. 49. Effect of infection with actinomycetes of the genus Frankia for alder growth: A. B - plants infected Frankia; b- uninfected plant (no: S. O. Suetin) up. The first type of nodules is observed in alder and sea buckthorn, the second - in casuarina. It has been established that nitrogen-fixing actinomycetes have a certain specificity to plants. For example, one group Frankia infects alder, waxweed and “sweet” fern (componia), the other infects oleaster, sea buckthorn and shepherdia.

Symbiont actinomycetes are capable of infecting only parenchyma cells of the root cortex. As with legumes, the microorganism penetrates the roots from the soil through root hairs, which curl as a result. At the site of infection, the walls of the root hair thicken and the hyphae that have penetrated the cell become covered with a thick sheath. As the hyphae move along the root hairs, the sheath thins and a capsule is formed around the hyphae, which is thought to be produced by both the plant and the actinomyest.

From the root hair, hyphae penetrate the epidermis and root cortex, causing division and hypertrophy of infected cells. As a rule, balls of hyphae fill the center of plant cells; expansion and division of the ends of the hyphae occur near the cell walls; in the latter case, specific structures are formed, the so-called vesicles(Fig. 50). A substance similar to leghemoglobin in leguminous plants is formed in the nodules. At the end of the growing season, the vesicles degrade, but hyphae remain in the plant cells, infecting

Rice. 50. Vesicles formed by mycelium Frankia in the alder nodules (after: I. Gardner) new tissues are harvested in the spring. Typically, in symbiosis with non-leguminous plants, the energy of nitrogen fixation by actinomycetes of the genus Frankia more than in the nodule bacteria of leguminous plants.

Nodules were found in a large group of herbaceous plants - cereals, sedges, buttercups, etc. In the nodules of these plants, microbial associations were identified, consisting of two or three types of microorganisms, which were represented by gram-positive and gram-negative bacteria. It has been established that nitrogen fixation occurs in the nodules, but the role of individual bacteria in it has not yet been determined.

Recently, from nodules on non-legume plants - a tropical shrub Trema orientalis(nettle family) and close to it Parasponia parviflora - Bacteria close to legume nodule bacteria were isolated. These bacteria are capable of infecting legume plants and forming nodules. They are classified as Rhizobium. From nodules on the leaves of tropical shrubs Pavetta And Psychotria nitrogen-fixing bacteria were isolated and assigned to the genus Klebsiella (Klebsiella rubacearum). Leaf nodules also enrich the plant with nitrogen. Therefore, in India, Sri Lanka and other countries the leaves Pavetta used as green manure.

Nitrogen-fixing symbionts enrich the soil with nitrogen to the following extent: annual legumes (beans, soybeans, vetch, beans, peas, lentils) accumulate 40-110 kg/ha of nitrogen per year), perennial legumes (clover, alfalfa) - 150-220, tropical legumes - Sesbania rostrata- from 324 (dry season) to 458 (wet season), non-legume plants - 150-300 kg/ha of nitrogen per year.

The kingdom “Bacteria” consists of bacteria and blue-green algae, the general characteristic of which is their small size and the absence of a nucleus separated by a membrane from the cytoplasm.

Who are bacteria

Translated from Greek “bakterion” means stick. For the most part, microbes are single-celled organisms invisible to the naked eye that reproduce by division.

Who discovered them

For the first time, a Dutch researcher who lived in the 17th century, Anthony Van Leeuwenhoek, was able to see the smallest single-celled organisms in a homemade microscope. He began studying the world around him through a magnifying glass while working in a haberdashery store.

Anthony Van Leeuwenhoek (1632 - 1723)

Leeuwenhoek subsequently focused on making lenses capable of magnification up to 300 times. In them he examined the smallest microorganisms, describing the information received and transferring what he saw to paper.

In 1676, Leeuwenhoek discovered and presented information about microscopic creatures, to which he gave the name “animalcules.”

What do they eat?

The smallest microorganisms existed on Earth long before the appearance of humans. They have a ubiquitous distribution, feeding on organic food and inorganic substances.

Based on the methods of assimilation of nutrients, bacteria are usually divided into autotrophic and heterotrophic. For existence and development, heterotrophs use waste products from the organic decomposition of living organisms.

Representatives of bacteria

Biologists have identified about 2,500 groups of different bacteria.

According to their form they are divided into:

• cocci having spherical outlines;
• bacilli - rod-shaped;
• vibrios that have curves;
• spirilla – spiral shape;
• streptococci, consisting of chains;
• staphylococci that form grape-like clusters.

According to the degree of influence on the human body, prokaryotes can be divided into:

• useful;
• harmful.

Microbes dangerous to humans include staphylococci and streptococci, which cause purulent diseases.

The bacteria bifido and acidophilus are considered beneficial, stimulating the immune system and protecting the gastrointestinal tract.

How do real bacteria reproduce?

Reproduction of all types of prokaryotes occurs mainly by division, followed by growth to the original size. Having reached a certain size, an adult microorganism splits into two parts.

Less commonly, reproduction of similar unicellular organisms is performed by budding and conjugation. When budding on the mother microorganism, up to four new cells grow, followed by the death of the adult part.

Conjugation is considered the simplest sexual process in unicellular organisms. Most often, bacteria that live in animal organisms reproduce in this way.

Bacteria symbionts

Microorganisms involved in digestion in the human intestine are a prime example of symbiont bacteria. Symbiosis was first discovered by the Dutch microbiologist Martin Willem Beijerinck. In 1888, he proved the mutually beneficial close coexistence of unicellular and legume plants.

Living in the root system, symbionts, feeding on carbohydrates, supply the plant with atmospheric nitrogen. Thus, legumes increase fertility without depleting the soil.

There are many successful symbiotic examples involving bacteria and:

• person;
• algae;
• arthropods;
• sea ​​animals.

Microscopic single-celled organisms assist the systems of the human body, help purify wastewater, participate in the cycle of elements and work to achieve common goals.

Why are bacteria classified into a special kingdom?

These organisms are characterized by their small size, lack of a formed nucleus, and exceptional structure. Therefore, despite their external similarity, they cannot be classified as eukaryotes, which have a formed cell nucleus limited from the cytoplasm by a membrane.

Thanks to all their features, in the 20th century scientists identified them as a separate kingdom.

The most ancient bacteria

The smallest single-celled organisms are considered the first life to emerge on Earth. Researchers in 2016 discovered buried cyanobacteria in Greenland that were about 3.7 billion years old.

In Canada, traces of microorganisms that lived approximately 4 billion years ago in the ocean have been found.

Functions of bacteria

In biology, between living organisms and their environment, bacteria perform the following functions:

• processing of organic substances into minerals;
• nitrogen fixation.

In human life, single-celled microorganisms play an important role from the first minutes of birth. They provide a balanced intestinal microflora, influence the immune system, and maintain water-salt balance.

Bacterial reserve substance

In prokaryotes, reserve nutrients accumulate in the cytoplasm. They accumulate under favorable conditions and are consumed during periods of fasting.

Bacterial reserve substances include:

• polysaccharides;
• lipids;
• polypeptides;
• polyphosphates;
• sulfur deposits.

The main sign of bacteria

The function of the nucleus in prokaryotes is performed by the nucleoid.

Therefore, the main characteristic of bacteria is the concentration of hereditary material in one chromosome.

Why are representatives of the kingdom of bacteria classified as prokaryotes?

The absence of a formed nucleus was the reason for classifying bacteria as prokaryotic organisms.

How bacteria survive unfavorable conditions

Microscopic prokaryotes are able to endure unfavorable conditions for a long time, turning into spores. There is a loss of water from the cell, a significant decrease in volume and a change in shape.

Spores become insensitive to mechanical, temperature and chemical influences. In this way, the property of viability is preserved and effective resettlement is carried out.

Conclusion

Bacteria are the oldest form of life on Earth, known long before the appearance of humans. They are present everywhere: in the surrounding air, water, and in the surface layer of the earth’s crust. Habitats include plants, animals and humans.

Active study of single-celled organisms began in the 19th century and continues to this day. These organisms are a major part of people's daily lives and have a direct impact on human existence.