Rhizobacteria are legumes’ best friends. All plants need nitrogen. Most can only get it from soil. But legumes, such as beans, can get it from air. This is thanks to rhizobacteria. These bacteria live in legumes’ roots. They turn nitrogen from air into a form the plant can use. Plants return the favor by giving the bacteria food and shelter.
Relevance to Humans and Ecosystems
Many bacteria in the family Rhizobiaceae (a clade of proteobacteria) are able to infect and establish a nitrogen-fixing symbiosis on the roots of leguminous plants. This symbiosis is of economic importance to humans in a variety of ways and decreases the need for nitrogen fertilizer for some key agriculturally important plants (e.g. soybean and alfalfa). The establishment of the symbiosis involves complex interactions between the plant host and the bacteria, resulting in the formation of a novel organ, the nodule, which the bacteria colonize as intracellular symbionts. Stacey et al. (2006) reviewed recent discoveries relating to how this symbiosis is established.
The Rhizobiaceae are a family of proteobacteria, including many species of rhizobia, as well as plant parasites such as Agrobacterium. The Rhizobiaceae are, like all Proteobacteria, Gram-negative. They are aerobic and the cells are usually rod-shaped. Many species of the Rhizobiaceae are diazotrophs, they are able to fix nitrogen and are symbiotic with plant roots.
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)  and National Center for Biotechnology Information (NCBI) and the phylogeny is based on 16S rRNA-based LTP release 106 by The All-Species Living Tree Project 
- J.P. Euzéby. "Proteobacteria (scroll down for Rhizobiaceae)". List of Prokaryotic names with Standing in Nomenclature (LPSN) . Retrieved 2012-05-02.
- Garrity, George M.; Brenner, Don J.; Krieg, Noel R.; Staley, James T. (eds.) (2005). Bergey's Manual of Systematic Bacteriology, Volume Two: The Proteobacteria, Part C: The Alpha-, Beta-, Delta-, and Epsilonproteobacteria. New York, New York: Springer. ISBN 978-0-387-24145-6.
- Sayers et al. "Rhizobiaceae". National Center for Biotechnology Information (NCBI) taxonomy database . Retrieved 2012-05-02.
- All-Species Living Tree Project."16S rRNA-based LTP release 106 (full tree)". Silva Comprehensive Ribosomal RNA Database . Retrieved 2012-05-02.
- These species were formerly classified in the genus Agrobacterium.
- This is the type species for the genus.
- Arthrobacter viscosus is currently classified in the Micrococcaceae. See Arthrobacter.
- Species found in the genera Aurantimonas, Aureimonas, Fulvimarina, and Martelella are all currently classified in the Aurantimonadaceaea.
- The species in the genus Aureimonas were formerly classified in the genus Aurantimonas.
- Beijerinckia fluminensis is currently classified in the Beijerinckiaceae.
- This includes Agrobacterium tumefaciens (Smith and Townsend 1907) Conn 1942.
- Blastobacter capsulatus is currently classified in the Bradyrhizobiaceae.
- These species were formerly classified in the genus Sinorhizobium.
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