Rhizobia

Rhizobia are soil bacteria that associate with legumes, form root nodules, and fix atmospheric nitrogen into compounds plants can use.

Nitrogen fixation: The conversion of atmospheric nitrogen gas into chemically available nitrogen compounds. Rhizobia perform this conversion inside legume nodules.
Legume: A plant in the family Fabaceae, many members of which form nitrogen-fixing root nodules. Legumes provide the roots and carbon compounds that support rhizobial symbiosis.
Inoculant: A preparation of beneficial microorganisms applied to seeds, roots, or soil. Rhizobial inoculants introduce effective strains where compatible bacteria are scarce or ineffective.
Bradyrhizobium: A genus of slow-growing nitrogen-fixing bacteria that includes important legume symbionts. It is one major rhizobial lineage, often associated with soybean and other legumes.
Nodulation: The development of specialized root structures in which plants host nitrogen-fixing bacteria. It is the distinctive process that establishes rhizobial residence in legume roots.
Bacteria: A domain of single-celled organisms whose cells lack a membrane-bound nucleus. Rhizobia are bacterial partners, not a single species or genus.
Crop rotation: The planned sequence of different crops grown on the same land over time. Including legumes can add biologically fixed nitrogen to rotations.
Rhizobium leguminosarum: A bacterial species complex that forms nitrogen-fixing symbioses with several legume groups. Its distinct host-associated biovars illustrate variation within rhizobia.
Leghemoglobin: An oxygen-binding protein in legume root nodules that helps maintain conditions for nitrogen fixation. It limits free oxygen while supplying enough for bacterial respiration.
Symbiosis: A close, sustained association between organisms of different species. Rhizobial life in nodules is a specialized plant–microbe symbiosis.

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Acacia melanoxylonRelated: These symbiotic bacteria support nitrogen acquisition in this leguminous tree.