Rhizobium

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Rhizobium

	Rhizobium - species invade the root hairs of leguminous plants. The bacteria aggregate as threads and penetrate the plant cells. The presence of bacteria stimulates the multiplication of infected cells, resulting in the formation of nodules. The legume, the bacteria, and the nodule constitute the system for the symbiotic nitrogen fixation, where both the bacteria and the plant benefit by the association.
The bacteria obtain their nutrients and source of energy from the plant, and in turn, fix atmospheric nitrogen and make it available to the plant. Bacteria isolated from root nodules of one legume are not necessarily capable of producing nodules on another legume. A certain degree of specificity, therefore, exists between the bacteria and legumes. A number of bacterial species are named on the basis of susceptible plants. Generally eight groups have been recognised.
Rhizobium species of proper type which will form a symbiotic association with a particular legume may be absent in the soil. Legume seeds before planting are, therefore, inoculated with strains of Rhizobium of known effectiveness. This is called preinoculation.
Bacterial cultures for this purpose are available commercially. Seeds inoculated with such cultures assure the presence of desirable strains of Rhizobia as soon as young rootlets are formed.

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Sulphur Cycle Ammonification in Soil Nitrification in Soil Nitrate Reduction in Soil Denitrification in Soil Nitrogen Fixation Symbiotic Nitrogen Fixation Rhizobium Specificity of Bacteria and Legumes Non-Symbiotic Nitrogen Fixation Non-symbiotic Nitrogen Fixing Microorganisms Mechanism of Nitrogen Fixation Oxidation of Sulphur and Sulphur Compounds by Bacteria