Nodule bacteria - symbiotic organisms fixing nitrogen

Nodule bacteria aremicroorganisms that belong to the genus Rhizobium (literally from the Greek. - "living on the roots"). They are embedded in the root system of the plant and live there. However, they are not parasites, since not only bacteria, but also the representative of the flora receives benefits. Such mutually beneficial existence of organisms is called symbiosis. In this case, the plants additionally receive atmospheric nitrogen, which is “caught” by microorganisms, and the bacteria themselves - carbohydrates and minerals. There is an opinion that these prokaryotes settle only in the roots of the legume family in the roots, but this is not the case. There are other plants whose roots serve as a habitat for nodule prokaryotes — for example, alder, forest reed, etc.

For organisms of the genus Rhizobium characteristicpolymorphism, that is, the forms of bacteria are very diverse. These microorganisms can be mobile and immobile, in the form of a cocci or stick, filiform, oval. Most often, young prokaryotes have a rod-like shape, which changes with growth and age due to accumulation of nutrients and immobilization. In its life cycle, the microorganism goes through several stages, which can be judged by its appearance. Initially, this is the form of a stick, then the so-called "belted stick" (it has belts with fatty inclusions) and, finally, the bacteriode is a large fixed cell of irregular shape.

Nodule bacteria have specificity, i.e. they are able to settle only in

a particular group or type of plant.This property of microorganisms formed genetically. Also important is efficiency - the ability to accumulate atmospheric nitrogen in sufficient quantity for its host plant. This property is not permanent and may change due to habitat conditions.

About how nodule bacteria get intoroot, there is no consensus, but there are a number of hypotheses about the mechanism of their penetration. Thus, some scientists believe that prokaryotes penetrate into the root through damage to its tissues, while others speak of penetration through root hairs. There is also an auxin hypothesis - the assumption of satellite cells that help bacteria invade the root cells.

The introduction itself occurs in two phases: first, the infection of root hairs, then the formation of nodules. The duration of the phases is different and depends on the specific type of plant.

The value of bacteria that are able to fixnitrogen is great for agriculture, since it is these organisms that can increase yields. From these microorganisms prepare bacterial fertilizer, which is used for treating the seeds of legumes, which contributes to more rapid infection of the roots. Various species of the moth family, when planted even on poor soils, do not require additional nitrogen fertilization. Thus, 1 ha of legumes “in work” with nodule bacteria during the year converts 100-400 kg of nitrogen into a bound state.

Thus, nodule bacteria are symbiotic organisms that are very important not only in the life of the plant, but also the nitrogen cycle in nature.