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Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant cells to form root nodules, where they convert atmospheric nitrogen into ammonia using the enzyme nitrogenase.
Rhizobia are a "group of soil bacteria that infect the roots of legumes to form root nodules". [2] Rhizobia are found in the soil and, after infection, produce nodules in the legume where they fix nitrogen gas (N 2) from the atmosphere, turning it into a more readily useful form of nitrogen. From here, the nitrogen is exported from the nodules ...
The host plant provides the bacteria with amino acids so they do not need to assimilate ammonia. [5] The amino acids are then shuttled back to the plant with newly fixed nitrogen. Nitrogenase is an enzyme involved in nitrogen fixation and requires anaerobic conditions. Membranes within root nodules are able to provide these conditions.
The rhizobia, which fix nitrogen and are symbiotic with plant roots, appear in several different families. The four families Nitrobacteraceae, Hyphomicrobiaceae, Phyllobacteriaceae, and Rhizobiaceae contain at least several genera of nitrogen-fixing, legume-nodulating, microsymbiotic bacteria. Examples are the genera Bradyrhizobium and Rhizobium.
Some bacteria found in the family are used for plant nutrition and collectively make up the rhizobia. Other bacteria such as Agrobacterium tumefaciens and Rhizobium rhizogenes severely alter the development of plants in their ability to induce crown galls or hairy roots, respectively. [2]
In response to root exudates, rhizobia produce Nod signalling factors that are recognized by legumes and induce the formation of nodules on plant roots. [28] Within these structures, Rhizobium fix atmospheric nitrogen into ammonia that is then used by the plant. In turn, plants provide the bacteria with a carbon source to energize the nitrogen ...
Rhizobium leguminosarum is a bacterium which lives in a mutualistic symbiotic relationship with legumes, and has the ability to fix free nitrogen from the air. [2] R. leguminosarum has been very thoroughly studied—it has been the subject of more than a thousand publications.
Rhizobium lentis are rod-shaped bacteria found in the soil. They require oxygen and do not form spores. [1] Rhizobium lentis grow well on YEMA medium agar, where they form colonies which are circular, convex and creamy white. These bacteria grow at 12–37 °C but can survive at temperatures as low as 4 °C. [1] Strains grow well at pH 5.5 to 8.2.