Rhizobium

Rhizobium is a genus of soil bacteria that forms nitrogen-fixing root nodules with many legume species. Its members convert atmospheric nitrogen into compounds their plant hosts can use.

Legume–rhizobium symbiosis: A mutualistic association in which legumes house nitrogen-fixing bacteria in root nodules. This broader partnership explains how Rhizobium benefits plants while receiving carbon and shelter.
Symbiosis island: A mobile genomic region carrying genes that can confer traits required for symbiotic nitrogen fixation. In some rhizobia, transferred symbiosis islands supply the machinery for nodulation and fixation.
Rhizobium inoculant: A preparation of selected rhizobial strains applied to legume seed or soil to promote nodulation. Inoculants introduce effective symbiotic strains where compatible bacteria are scarce or ineffective.
Rhizobium leguminosarum: A species of Rhizobium that forms nitrogen-fixing nodules on several legumes, including peas and clover. It is a well-studied model for host recognition and symbiotic gene regulation.
Nodulation factor: A bacterial lipochitooligosaccharide signal that triggers nodule development in compatible plants. Rhizobial Nod factors initiate the host responses that lead to infection and nodule formation.
Nod genes: Bacterial genes that produce or regulate factors involved in legume nodulation. These genes encode the signaling system that determines whether a plant recognizes a rhizobial partner.
Biological nitrogen fixation: The conversion of atmospheric nitrogen into biologically available compounds by living organisms. Rhizobium is a major agricultural example of this natural source of reactive nitrogen.
Rhizobium etli: A rhizobial species commonly associated with common bean. Its bean symbiosis illustrates how rhizobial partnerships vary among legume hosts.
Root nodule: A specialized plant organ that houses symbiotic nitrogen-fixing bacteria. Rhizobium establishes the compartment where bacterial nitrogen fixation occurs.
Nif genes: Genes encoding nitrogenase and associated functions required for biological nitrogen fixation. Their products enable Rhizobium to reduce atmospheric nitrogen within nodules.

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