What are nodule bacteria. Nodule bacteria in legumes

Nodule bacteria live with leguminous plants in symbiosis, that is, they bring mutual benefit to each other: nodule bacteria assimilate atmospheric nitrogen and convert it into compounds that can be used by leguminous plants; plants, in turn, supply nodule bacteria with substances containing carbon.

In appearance, nodule bacteria are usually small rods measuring 1.2-3 microns in length and 0.5-0.9 microns in width. In the process of life, they go through a complex and rather long development cycle for such small creatures, consisting of various phases, or stages. Depending on the phase of development, the appearance of bacteria also changes. Forms appear in the form of balls (cocci) or sticks, mobile or motionless.

Outside nodules (on artificial nutrient media), nodule bacteria can develop at temperatures from 0 to + 37°C, and the most favorable (optimal) temperatures for them are +20-31°C. best development usually observed in a neutral environment (at pH 6.5-7.2). All nodule bacteria have approximately the same resistance to the alkaline reaction of the environment, but they treat acidic soils in completely different ways.

In most cases, the acidic reaction of the soil adversely affects the vital activity of nodule bacteria, in acidic soils inactive or inefficient (non-fixing air nitrogen) races of these bacteria are formed. An interesting physiological feature of nodule bacteria is their ability to synthesize various vitamins and growth substances. Studying the possibility of nitrogen fixation by nodule bacteria when grown on artificial nutrient media, scientists obtained last years positive results. However, for agricultural practice, the ability of bacteria to fix nitrogen while in the nodules of legumes is important.

The first researchers of nodule bacteria assumed that these bacteria could cause the formation of nodules in most types of legumes. But then it was found that nodule bacteria have specificity, they settle in the plant in strict accordance with their needs. One or another race of nodule bacteria can enter into symbiosis with leguminous plants of only a certain species.

Currently, nodule bacteria are divided into the following groups (according to the plants on which they settle): 1) nodule bacteria of alfalfa and sweet clover; 2) nodule bacteria of clover; 3) root nodule bacteria of peas, vetch, chin and fodder beans; 4) soy nodule bacteria; 5) nodule bacteria of lupine and seradella; 6) bean nodule bacteria; 7) nodule bacteria of peanut, cowpea, cowpea, etc.

The specificity of nodule bacteria of different groups is not the same. While clover nodule bacteria are distinguished by very strict specificity, the same cannot be said about pea nodule bacteria.

A. A. Imshenetsky.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what "Nodule bacteria" is in other dictionaries:

- (Rhizobium), a genus of nitrogen-fixing bacteria that form nodules on the roots of many others. legume plants. Inside nodules K. b. assimilate they say. nitrogen, converting it into compounds absorbed by plants, which, in turn, provide bacteria with nutrition ... Biological encyclopedic dictionary

A genus of nitrogen-fixing bacteria that form nodules on the roots of many legumes. Absorb atmospheric molecular nitrogen and convert it into nitrogen compounds absorbed by plants, which, in turn, provide other plants ... ... Ecological dictionary

A genus of bacteria that form nodules on the roots of many leguminous plants and fix molecular nitrogen in the air under conditions of symbiosis with the plant. They do not form spores, they are aerobes. Enrich the soil with nitrogen. See also Nitrogen fixation… Big Encyclopedic Dictionary

Nodule bacteria. See rhizobia. (Source: "English Russian dictionary genetic terms. Arefiev V.A., Lisovenko L.A., Moscow: VNIRO Publishing House, 1995) ... Molecular biology and genetics. Dictionary.

nodule bacteria- rhizobia An extensive, genetically heterogeneous (in connection with this, the genus Rhyzobium is now subdivided into 3 4 independent genera) group of soil gram-negative microorganisms capable of entering into intracellular symbiosis with leguminous plants and ... ... Technical Translator's Handbook

Cross section of a soybean root nodule. Bacteria, lat. Bradyrhizobium japonicum, seed the roots and enter into a nitrogen-fixing symbiosis. Nodule bacteria ... Wikipedia

A genus of bacteria that form nodules on the roots of many leguminous plants and fix molecular nitrogen in the air under conditions of symbiosis with the plant. They do not form spores, they are aerobes. Enrich the soil with nitrogen. See also nitrogen fixation. * * * Nodule Bacteria… … encyclopedic Dictionary

nodule bacteria- symbiont bacteria that develop on the tissues of the roots of legumes and some other plants, capable of binding free nitrogen from the air and making it available to higher plants … Glossary of botanical terms

nodule bacteria- (Rhizobium), a genus of aerobic bacteria that settle in nodules on the roots of legumes and have the ability to absorb atm. nitrogen and enrich the soil with it. They live in symbiosis with plants, providing them with nitrogen and receiving carbon products from early ... Agricultural Encyclopedic Dictionary

nodule bacteria- (Rhizobium), a genus of aerobic bacteria that settle in nodules on the roots of leguminous plants and have the ability to absorb atmospheric nitrogen and enrich the soil with it. They live in symbiosis with plants, providing them with nitrogen and receiving from plants ... ... Agriculture. Big encyclopedic dictionary

Nodule bacteria belong to the genus Rhizobium. They have the ability to fix nitrogen from atmospheric air and synthesize organic nitrogen-containing compounds. These microorganisms form nodules on the roots of some leguminous plants, entering into a symbiosis. These bacteria convert nitrogen into compounds that are easily available for absorption by plants, and flowering plants, in turn, are sources of nutrients for nodule bacteria. Also this species bacteria is an important link in the process of soil enrichment with nitrogen.

After penetration into the root hair, the bacteria cause an intensive division of the root cells, resulting in the appearance of a nodule. The bacteria themselves develop in these nodules on the roots, participating in the assimilation of nitrogen. There they are transformed into branched forms - bacteroids that absorb molecular nitrogen, ammonium salts, amino acids, nitrates. Nodule bacteria use monosaccharides, disaccharides, alcohols, organic acids as a carbon source.

Nodule bacteria have sizes from 0.5 to 3 microns. They do not form a dispute, mobile, gram-negative. They need access to oxygen for the normal course of metabolic processes. Under laboratory conditions, colonies of nodule bacteria grow well at a temperature of 25 degrees on dense media. They have a characteristic rounded shape, mucous consistency, transparent.

Nodule bacteria live on the roots of 10% of plants from the legume family. And different types bacteria develop on the root system of certain higher plants. Vetch, broad beans, peas have Rh. Leguminosarum, in sweet clover, alfalfa - Rhizobium meliloti, in soybeans - Rh. Japonicum, in clover - Rh. trifolia. If the roots of legumes die off, and the nodules are destroyed, nodule bacteria do not die, but lead the life of saprophytes.

These bacteria absorb up to 300 kg of nitrogen per 1 ha from atmospheric air, while during their life activity more than 50 kg of nitrogen-containing compounds remain in the soil. In order to increase the number of nodule bacteria in the soil and, accordingly, the yield of cultivated leguminous plants, a bacterial agent, nitragin, is added when planting seeds, that is, they artificially infect legume seeds with nodule bacteria.

These microorganisms promote the release of nitrogen from air currents and convert it into useful compounds. Bacteria create nodules on the root system of a number of leguminous plants, falling into symbiosis. We understand today, nodule bacteria than enrich the soil.

Nitrogen is found not only in the atmosphere, but also in the earth's surface. And it is necessary to involve it in the general circulation. Nodule bacteria take an active part in such a cycle. They assimilate nitrogen from atmospheric masses and soil composition, process it into organic components that can be easily consumed by the plant world.
Plants are consumed by humans and animals, which over time release nitrogen elements into the air as a result of the onset of the denitrification process.

The role of bacteria in nitrogen supply

The saturation of the soil layer with nitrogen is the result of the activity of microscopic organisms, which include nodules. Previously, it was believed that this type of work was carried out exclusively by nodule organisms that could consume nitrogen from the air. And the main task in this was assigned to the leguminous vegetation, as the only source for the vital activity of bacteria. Today, this opinion has been revised, as in Lately a sufficient number of various microorganisms have been identified that contribute to the processing of nitrogen.

And yet, the main place in this process is given to the nodule detachment. It includes rhizobium. This species resembles a stick in its shape, does not create colonies, exists singly or in pairs. Meet certain types pathogenic for a person infected with AIDS.
The second representative is some of the actinomycetes living in the root systems of trees, which have the ability to create nodule processes for them.

Getting into the hairs of the roots, bacteria create an active division of their cells, during which nodules are created. Bacterial microorganisms themselves settle inside, develop and process nitrogen. And in the same nodule processes, bacteria are converted into branched forms capable of assimilating nitrogen, salts, amino acids, and nitrate components. In order to obtain carbon, microorganisms use alcohols, monosaccharides, organic acids.

Living conditions

Representatives of nodules reach sizes from 0.5 to 3 microns. They do not create spores, are quite mobile, gram-negative. To metabolic process passed without disturbances, it is necessary to provide a constant supply of oxygen. When breeding bacteria in laboratory conditions, the greatest results can be achieved if temperature regime at least twenty-five degrees Celsius. The forms are rounded, seemingly transparent, the consistency is slimy.

Such bacteria find their development on the root systems of legumes, the number of which can reach ten percent of total number. At the same time, certain types of these organisms of microscopic forms are created in various representatives.

With the death of the roots, the destruction of the tubers also occurs. But this does not entail the death of bacteria. They continue to exist in the soil and process nitrogen masses.

Bacterial colonies are able to absorb about three hundred kilograms of nitrogen per hectare of land, and as a result of their vital processes, more than fifty kilos of compounds containing nitrogen are retained in the soil. That is why they are used so that plants can consume useful compounds that are harmful to health from the earth. Planting other crops after legumes such as cabbage, the harvest will be excellent.

For crop rotation, legumes are used as they are excellent for this. They emerge early, being cold-resistant and their roots loosen the ground. More often used peas, annual, vetch, clover, alfalfa, chickpeas, beans and soybeans, beans, lentils, sweet clover, goat's rue, field peas, etc. greatly enrich the soil with nitrogen. Embedding in upper layer soil greenery of these plants, replaces fertilizer with manure. Plants are cold-resistant, sprout early, and their roots powerfully loosen the ground.

In order to increase nodule bacteria in the soil and increase the yield of legumes, nitragin can be applied to the ground when planting. With the help of this tool, artificial infection of the seed fund with nodule bacteria is carried out.

Distribution of nodule bacteria in nature

Being symbiotic organisms, nodule bacteria spread in soils, accompanying certain types of leguminous plants. After the destruction of the nodules, the cells of nodule bacteria enter the soil and begin to exist at the expense of various organic substances, like other soil microorganisms. The almost ubiquitous distribution of nodule bacteria is evidence of their high degree of adaptability to various soil and climatic conditions, the ability to lead a symbiotic and saprophytic way of life.

Schematizing the currently available data on the distribution of nodule bacteria in nature, we can make the following generalizations.

In virgin and cultivated soils, they are usually present in large quantities nodule bacteria of those species of leguminous plants that are found in the wild flora or cultivated long time in this locality. The number of nodule bacteria is always the highest in the rhizosphere of leguminous plants, somewhat less in the rhizosphere of other species, and few in the soil away from the roots.

Both effective and ineffective nodule bacteria are found in soils. There is a lot of evidence that the long-term saprophytic existence of nodule bacteria, especially in soils with unfavorable properties(acidic, saline), leads to a decrease and even loss of bacterial activity.

Rice. 1 - Nodules on alder roots (according to J. Becking)

Cross-infection of different species of leguminous plants often leads in nature and agricultural practice to the appearance of nodules on the roots that do not actively fix molecular nitrogen. This, as a rule, depends on the absence of the corresponding types of nodule bacteria in the soil.

Especially often this phenomenon is observed when using new species of leguminous plants, which are either infected with ineffective species of Cross-group bacteria or develop without nodules.

Rice. 2 - Nodules on the roots of tribulus (according to O. Allen)

Nodule bacteria are used for industrial production nitragin, used to treat the seeds of legumes. They were first discovered by M. S. Voronin in 1866. Later, M. V. Beyerink (1888) isolated them in pure culture and studied in detail by microbiologists and physiologists. Bacteria enter the roots of leguminous plants through the root hair and penetrate into the inner integument of the root, into the parenchyma, causing increased cell division and proliferation. On the roots, ugly growths are formed, called nodules, or nodules. Bacteria digest first nutrients plants and somewhat inhibit its growth. Then, as the nodule tissue grows, a symbiosis is established between bacteria and higher plants. Bacteria receive carbonaceous food (sugar) and minerals from the plant, and in return provide it with nitrogenous compounds.

Nodule bacteria settle in the soil, multiply, and penetrate the root cells through holes in the root hairs of leguminous plants. In the cells there is an increased reproduction of nodule bacteria and in parallel there is an intensive division of root cells infected with nodule bacteria.

Nodule bacteria supply leguminous plant nitrogen. The plant utilizes this bound nitrogen and in turn supplies the nodule bacteria with the carbon-containing organic matter they need. Nodule bacteria can use various sugars and alcohols as a carbon source.

Nodule bacteria are microaerophiles (they develop with small amounts of oxygen in the environment), however, they prefer aerobic conditions. Nodule bacteria that have emerged from the infection thread continue to multiply in the host tissue. The bulk of bacteria multiply in the cytoplasm of the cell, and not in the infection thread. They develop most intensively when the soil reaction is close to neutral. Therefore, when sowing legumes on acidic soils, along with the inoculation of seeds, soil liming is necessary. Inoculation without liming has very little effect on yield and protein content.

Nodule bacteria are capable of favorable conditions in one season to accumulate up to 200 - 300 kg / ha of nitrogen.

Young nodule bacteria in pure culture on nutrient media usually have a rod-shaped shape (Fig. 2, 3), the size of the rods is approximately 0 5 - 0 9 X 1 2 - 3 0 μm, mobile, multiply by division

In addition to nodule bacteria, other microorganisms that can assimilate free nitrogen from the air also live in the soil; they do not live on the roots of plants, but near them. All other nutrients needed by these microbes, they absorb on their own, and not at the expense of plant juices, as is inherent nodule plants. Azotobacter is the most important microorganism living in the soil, capable of assimilating atmospheric nitrogen. These bacteria can live under favorable conditions of humidity, good air flow, suitable temperature and acidity of the soil. Azotobacter requirements for thermal regime and soil moisture are about the same as the requirements cultivated plants, but it is more sensitive to soil acidity than most plants.