Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of legumes and Parasponia.
Rhizobium is a genus of gram-negative, motile bacteria whose members are most notable for their ability to establish a symbiotic relationship with leguminous plants, such as peas, soybeans, and alfalfa. This relationship leads to the establishment of specialized structures called nodules. In these structures the bacteria are able to convert atmospheric nitrogen into ammonia, a process called nitrogen fixation. The ammonia is used by the plant as a nitrogen source. Other genera, such as Azorhizobium and Bradyrhizobium can also nodulate leguminous plants and, together with Rhizobium, they are referred to as rhizobia. Members of the genus Rhizobiumspecifically form root nodules, but some other rhizobia can also form nodules on the plant stems.