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Rhizobium tropici on an agar plate (Tryptone — Yeast extract agar).
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Pseudomonadota
Class: Alphaproteobacteria
Order: Hyphomicrobiales
Family: Rhizobiaceae
Genus: Rhizobium
Frank 1889 (Approved Lists 1980)[1][2]
Type species
Rhizobium leguminosarum
(Frank 1879) Frank 1889 (Approved Lists 1980)

See text

Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants.

The bacteria colonize plant cells to form root nodules, where they convert atmospheric nitrogen into ammonia using the enzyme nitrogenase. The ammonia is shared with the host plant in the form of organic nitrogenous compounds such as glutamine or ureides.[3] The plant, in turn, provides the bacteria with organic compounds made by photosynthesis. This mutually beneficial relationship is true of all of the rhizobia, of which the genus Rhizobium is a typical example.[4] Rhizobium is also capable of solubilizing phosphate.[5]


Martinus Beijerinck was the first to isolate and cultivate a microorganism from the nodules of legumes in 1888.[6] He named it Bacillus radicicola, which is now placed in Bergey's Manual of Determinative Bacteriology under the genus Rhizobium.


Rhizobium forms a symbiotic relationship with certain plants, such as legumes, fixing nitrogen from the air into ammonia, which acts as a natural fertilizer for the plants. The Agricultural Research Service is conducting research involving the genetic mapping of various rhizobial species with their respective symbiotic plant species, like alfalfa or soybean. The goal of this research is to increase the plants’ productivity without using fertilizers.[7]

In molecular biology, Rhizobium has been identified as a contaminant of DNA extraction kit reagents and ultrapure water systems, which may lead to its erroneous appearance in microbiota or metagenomic datasets.[8] The presence of nitrogen-fixing bacteria as contaminants may be due to the use of nitrogen gas in ultra-pure water production to inhibit microbial growth in storage tanks.[9]


The genus Rhizobium comprises the following species:[10]

Species in "parentheses" have been described, but not validated according to the Bacteriological Code.[10]


The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN).[10] The phylogeny is based on whole-genome analysis.[16]


  1. ^ This species belongs in Pararhizobium, but hasn't been formally transferred, yet.
  2. ^ a b c d e These species belong in Neorhizobium, but haven't been formally transferred, yet.
  3. ^ This species belongs in Peteryoungia, but hasn't been formally transferred, yet.


  1. ^ Frank, B. (1889). "Über die Pilzsymbiose der Leguminosen". Berichte der Deutschen Botanischen Gesellschaft. 7: 332–346.
  2. ^ Skerman, VB; McGowan, V; Sneath, PH (1980). "Approved lists of bacterial names". International Journal of Systematic Bacteriology. 30: 225–420. doi:10.1099/00207713-30-1-225.
  3. ^ Thilakarathna, Malinda S.; Raizada, Manish N. (2018-01-01). "Visualizing Glutamine Accumulation in Root Systems Involved in the Legume–Rhizobia Symbiosis by Placement on Agar Embedded with Companion Biosensor Cells". Phytobiomes Journal. 2 (3): 117–128. doi:10.1094/PBIOMES-07-18-0031-TA.
  4. ^ Sawada, Hiroyuki; Kuykendall, L. David; Young, John M. (June 2003). "Changing concepts in the systematics of bacterial nitrogen-fixing legume symbionts". The Journal of General and Applied Microbiology. 49 (3): 155–79. doi:10.2323/jgam.49.155. PMID 12949698.
  5. ^ Sridevi, M; Mallaiah, KV (March 2009). "Phosphate solubilization by Rhizobium strains". Indian Journal of Microbiology. 49 (1): 98–102. doi:10.1007/s12088-009-0005-1. PMC 3450048. PMID 23100757.
  6. ^ Beijerinck, Martinus W. (1888). "Die Bacteriender Papilionaceenknöllchen". Bot.Ztg. 46.
  7. ^ "Marvelous Microbe Collections Accelerate Discoveries To Protect People, Plants—and More!". Agricultural Research. United States Department of Agriculture. January 2010. Retrieved 10 August 2018.
  8. ^ Salter, Susannah J.; Cox, Michael J.; Turek, Elena M.; Calus, Szymon T.; Cookson, William O.; Moffatt, Miriam F.; et al. (November 2014). "Reagent and laboratory contamination can critically impact sequence-based microbiome analyses". BMC Biology. 12: 87. bioRxiv 10.1101/007187. doi:10.1186/s12915-014-0087-z. ISSN 1741-7007. PMC 4228153. PMID 25387460.
  9. ^ Kulakov, Leonid A.; McAlister, Morven B.; Ogden, Kimberly L.; Larkin, Michael J.; O'Hanlon, John F. (April 2002). "Analysis of bacteria contaminating ultrapure water in industrial systems". Applied and Environmental Microbiology. 68 (4): 1548–1555. doi:10.1128/AEM.68.4.1548-1555.2002. PMC 123900. PMID 11916667.
  10. ^ a b c Euzéby, JP; Parte, AC. "Rhizobiaceae". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved September 16, 2022.
  11. ^ Diange, Eboa Adolf; Lee, Sang-Seob (June 2013). "Rhizobium halotolerans sp. nov., Isolated from chloroethylenes contaminated soil". Current Microbiology. 66 (6): 599–605. doi:10.1007/s00284-013-0313-x. PMID 23377488. S2CID 17809044.
  12. ^ Kesari, Vigya; Ramesh, Aadi Moolam; Rangan, Latha (2013). "Rhizobium pongamiae sp. nov. from root nodules of Pongamia pinnata". BioMed Research International. 2013: 165198. doi:10.1155/2013/165198. PMC 3783817. PMID 24078904.
  13. ^ Xu, Lin; Zhang, Yong; Deng, Zheng Shan; Zhao, Liang; Wei, Xiu Li; Wei, Ge Hong (March 2013). "Rhizobium qilianshanense sp. nov., a novel species isolated from root nodule of Oxytropis ochrocephala Bunge in China". Antonie van Leeuwenhoek. 103 (3): 559–65. doi:10.1007/s10482-012-9840-x. PMID 23142858. S2CID 18660422.
  14. ^ Wang, Fang; Wang, En Tao; Wu, Li Juan; Sui, Xin Hua; Li, Ying Li; Chen, Wen Xin (November 2011). "Rhizobium vallis sp. nov., isolated from nodules of three leguminous species". International Journal of Systematic and Evolutionary Microbiology. 61 (11): 2582–2588. doi:10.1099/ijs.0.026484-0. PMID 21131504.
  15. ^ Silva, Claudia; Vinuesa, Pablo; Eguiarte, Luis E; Souza, Valeria; Martínez-Romero, Esperanza (November 2005). "Evolutionary genetics and biogeographic structure of Rhizobium gallicum sensu lato, a widely distributed bacterial symbiont of diverse legumes". Molecular Ecology. 14 (13): 4033–50. doi:10.1111/j.1365-294X.2005.02721.x. PMID 16262857. S2CID 16668742.
  16. ^ Hördt, Anton; López, Marina García; Meier-Kolthoff, Jan P.; Schleuning, Marcel; Weinhold, Lisa-Maria; Tindall, Brian J.; Gronow, Sabine; Kyrpides, Nikos C.; Woyke, Tanja; Göker, Markus (7 April 2020). "Analysis of 1,000+ Type-Strain Genomes Substantially Improves Taxonomic Classification of Alphaproteobacteria". Frontiers in Microbiology. 11: 468. doi:10.3389/fmicb.2020.00468. PMC 7179689. PMID 32373076.

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