Nodule bacteria are microorganisms that belong to the genus Rhizobium (literally from Greek - "living on the roots"). They are introduced into the root system of the plant and live there. At the same time, they are not parasites, since not only bacteria, but also the representative of the flora itself benefits. This mutually beneficial existence of organisms is called symbiosis. In this case, 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 in the roots only of representatives of the legume family, but this is not so. There are other plants whose roots serve as a habitat for nodule prokaryotes - for example, alder, forest reed grass, etc.
Organisms of the genus Rhizobium are characterized by polymorphism, i.e., the forms of bacteria are very diverse. Datamicroorganisms can be mobile and immobile, have the shape of a coccus or rod, filamentous, oval. Most often, young prokaryotes have a rod-shaped shape, which changes with growth and age due to the accumulation of nutrients and immobilization. In its life cycle, a microorganism goes through several stages, which can be judged by its appearance. Initially, this is the form of a stick, then the so-called "girdled stick" (has belts with fatty inclusions) and, finally, bacteriod - a large immobile cell of irregular shape.
Nodule bacteria are specific, i.e. they are able to settle only in
of a certain group or species of plants. This property in microorganisms was formed genetically. Also important is efficiency - the ability to accumulate atmospheric nitrogen in sufficient quantities for its host plant. This property is not permanent and may change due to habitat conditions.
There is no consensus on how nodule bacteria enter the root, 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 the root hairs. There is also an auxin hypothesis - the assumption of satellite cells that help bacteria invade root cells.
The very same implementation occurs in two phases: first - infection of the root hairs, then -nodulation. The duration of the phases is different and depends on the specific type of plant.
The importance of bacteria that are able to fix nitrogen is great for agriculture, because it is these organisms that can increase crop yields. From these microorganisms, a bacterial fertilizer is prepared, which is used to treat legume seeds, which contributes to a more rapid infection of the roots. Various species of the moth family, when planted, even on poor soils, do not require additional application of nitrogen fertilizers. So, 1 hectare of legumes "in work" with nodule bacteria converts 100-400 kg of nitrogen into a bound state during the year.
Thus, nodule bacteria are symbiotic organisms that are very important not only in plant life, but also in the nitrogen cycle in nature.
