Definition of Rhizobia:

Rhizobia are a group of Gram-negative soil bacteria that form a symbiotic relationship with the roots of leguminous plants (e.g., soybeans, peas, alfalfa). Some strains can also establish symbiosis with non-leguminous plants (e.g., alders, bayberries). These rod-shaped bacteria can live independently in soil; under specific conditions, they can invade plant root systems and induce the formation of root nodules, serving as core microorganisms in the biological nitrogen fixation system.