''Rhizobium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

that fix nitrogen. ''Rhizobium'' species form an endosymbiotic

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmos ...

association with roots of (primarily)

legumes A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock fo ...

and other flowering plants. The bacteria colonize plant cells within

root nodule Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known a ...

s, where they convert atmospheric nitrogen into

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

using the enzyme nitrogenase and then provide organic nitrogenous compounds such as glutamine or ureides to the plant. The plant, in turn, provides the bacteria with

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

s made by

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. This mutually beneficial relationship is true of all of the

rhizobia Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. In gene ...

, of which the genus ''Rhizobium'' is a typical example. ''Rhizobium'' is also capable to solubilize phosphorus.

History

Martinus Beijerinck was the first to isolate and cultivate a

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

from the nodules of legumes in 1888. He named it ''Bacillus radicicola'', which is now placed in ''

Bergey's Manual of Determinative Bacteriology ''Bergey's Manual of Systematic Bacteriology'' is the main resource for determining the identity of prokaryotic organisms, emphasizing bacterial species, using every characterizing aspect. The manual was published subsequent to the ''Bergey's Manu ...

'' under the genus ''Rhizobium''.

Research

''Rhizobium'' forms a symbiotic relationship with certain plants such as legumes, fixing nitrogen from the air into

, which acts as a natural fertilizer for the plants. Current research is being conducted by

Agricultural Research Service The Agricultural Research Service (ARS) is the principal in-house research agency of the United States Department of Agriculture (USDA). ARS is one of four agencies in USDA's Research, Education and Economics mission area. ARS is charged with ext ...

microbiologists to discover a way to use ''Rhizobium''’s biological nitrogen fixation. This research involves the

genetic mapping Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separ ...

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. In molecular biology, ''Rhizobium'' has also 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. 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.

Species

The genus ''Rhizobium'' comprises the following species: * '' Rhizobium acidisoli'' Román-Ponce ''et al''. 2016 * '' Rhizobium aegyptiacum'' Shamseldin ''et al''. 2016 * '' Rhizobium aethiopicum'' Aserse ''et al''. 2017 * '' Rhizobium alamii'' Berge ''et al''. 2009 * "'' Rhizobium album''" Hang ''et al''. 2019 * "'' Rhizobium albus''" Li ''et al''. 2017 * '' Rhizobium altiplani'' Baraúna ''et al''. 2016 * '' Rhizobium alvei'' Sheu ''et al''. 2015 * ''

Rhizobium anhuiense ''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 ...

'' Zhang ''et al''. 2015 * '' Rhizobium aquaticum'' Máthé ''et al''. 2019 * "''

Rhizobium arachis ''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 ...

''" Wang et al. 2001 * '' Rhizobium arenae'' Zhang ''et al''. 2017 * '' Rhizobium arsenicireducens'' Mohapatra ''et al''. 2020 * '' Rhizobium azooxidifex'' Behrendt ''et al''. 2016 * '' Rhizobium bangladeshense'' Rashid ''et al''. 2015 * '' Rhizobium binae'' Rashid ''et al''. 2015 * '' Rhizobium calliandrae'' Rincón-Rosales ''et al''. 2013 * ''

Rhizobium capsici ''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 ...

'' Lin ''et al''. 2015 * ''

Rhizobium cauense ''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 ...

'' Liu ''et al''. 2015 * '' Rhizobium cellulosilyticum'' García-Fraile ''et al''. 2007 * '' Rhizobium changzhiense'' Zhang ''et al''. 2021 * '' Rhizobium chutanense'' Huo ''et al''. 2019 * "'' Rhizobium cremeum''" Yang et al. 2022 * "'' Rhizobium croatiense''" Rajnovic et al. 2022 * "'' Rhizobium deserti''" Liu ''et al''. 2020 * '' Rhizobium dioscoreae'' Ouyabe ''et al''. 2020 * '' Rhizobium ecuadorense'' Ribeiro ''et al''. 2015 * '' Rhizobium endophyticum'' López-López ''et al''. 2010 * '' Rhizobium esperanzae'' Cordeiro ''et al''. 2017 * '' Rhizobium etli'' Segovia ''et al''. 1993 * '' Rhizobium favelukesii'' Torres Tejerizo ''et al''. 2016 * "'' Rhizobium flavescens''" Su ''et al''. 2021 * '' Rhizobium freirei'' Dall'Agnol ''et al''. 2013 * '' Rhizobium gallicum'' Amarger ''et al''. 1997 * ''

Rhizobium gei ''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 ...

'' Shi ''et al''. 2016 * "''

Rhizobium glycinendophyticum ''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 ...

''" Wang ''et al''. 2020 * '' Rhizobium grahamii'' López-López ''et al''. 2011 * '' Rhizobium hainanense'' Chen ''et al''. 1997 * '' Rhizobium halophytocola'' Bibi ''et al''. 2012 * "''

Rhizobium halotolerans ''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 ...

''" Diange and Lee 2013 * "'' Rhizobium hedysari''" Casella ''et al.'' 1986 * "'' Rhizobium hedysari''" Xu ''et al''. 2017 * "'' Rhizobium hedysarum''" Casella et al. 1984 * '' Rhizobium helianthi'' Wei ''et al''. 2015 * '' Rhizobium hidalgonense'' Yan ''et al''. 2020 * "''

Rhizobium indicum ''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 ...

''" Rahi ''et al''. 2020 * ''

Rhizobium indigoferae ''Rhizobium indigoferae'' is a Gram negative root nodule bacteria, which nodulates and forms nitrogen fixation, nitrogen-fixing Symbiosis, symbioses with ''Indigofera'' species. Its type strain is CCBAU 717 ...

'' Wei ''et al''. 2002 *'' Rhizobium jaguaris'' Rincón-Rosales ''et al''. 2013 * "'' Rhizobium kunmingense''" Shen ''et al''. 2010 * '' Rhizobium laguerreae'' Saïdi ''et al''. 2014 * ''

Rhizobium leguminosarum ''Rhizobium leguminosarum'' is a bacterium which lives in a mutualistic symbiotic relationship with legumes, and has the ability to fix free nitrogen from the air. ''R. leguminosarum'' has been very thoroughly studied—it has been the subject ...

'' (Frank 1879) Frank 1889 (Approved Lists 1980) * '' Rhizobium lemnae'' Kittiwongwattana & Thawai 2014 * ''

Rhizobium lentis ''Rhizobium lentis'' is a gram-negative bacteria, gram-negative bacterium which was isolated from root nodules of lentils in Bangladesh. Description ''Rhizobium lentis'' are Bacillus (shape), rod-shaped bacteria found in the soil. They Aerobi ...

'' Rashid ''et al''. 2015 * ''

Rhizobium leucaenae ''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 ...

'' Ribeiro ''et al''. 2011 * ''

Rhizobium lusitanum ''Rhizobium lusitanum'' is a Gram negative root nodule bacteria, specifically nodulating ''Phaseolus vulgaris ''Phaseolus vulgaris'', the common bean, is a herbaceous annual plant grown worldwide for its edible dry seeds or green, unripe p ...

'' Valverde ''et al''. 2006 * "''Candidatus'' Rhizobium massiliense" Greub ''et al''. 2004. * '' Rhizobium mayense'' Rincón-Rosales ''et al''. 2013 * '' Rhizobium mesoamericanum'' López-López ''et al''. 2011 * '' Rhizobium mesosinicum'' Lin ''et al''. 2009 * '' Rhizobium metallidurans'' Grison ''et al''. 2015 * '' Rhizobium miluonense'' Gu ''et al''. 2008 * '' Rhizobium mongolense'' van Berkum ''et al''. 1998 * '' Rhizobium multihospitium'' Han ''et al''. 2008 * ''

Rhizobium oryzicola ''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 ...

'' Zhang ''et al''. 2015 * "'' Rhizobium oryzihabitans''" Zhao ''et al''. 2020 * ''

Rhizobium pakistanense ''Rhizobium'' is a genus of Gram-negative soil bacteria that nitrogen fixation, fix nitrogen. ''Rhizobium'' species form an endosymbiont, endosymbiotic nitrogen fixation, nitrogen-fixing association with roots of (primarily) legumes and other fl ...

'' corrig. Khalid ''et al''. 2015 * "'' Rhizobium panacihumi''" Kang ''et al''. 2019 * '' Rhizobium paranaense'' Dall'Agnol ''et al''. 2014 * '' Rhizobium phaseoli'' Dangeard 1926 (Approved Lists 1980) * "'' Rhizobium phenanthrenilyticum''" Wen ''et al''. 2011 * ''

Rhizobium pisi ''Rhizobium pisi'' is a root nodule bacterium. References Rhizobiaceae {{Hyphomicrobiales-stub ...

'' Ramírez-Bahena ''et al''. 2008 * "'' Rhizobium pongamiae''" Kesari ''et al''. 2013 * ''

Rhizobium populi ''Rhizobium'' is a genus of Gram-negative soil bacteria that nitrogen fixation, fix nitrogen. ''Rhizobium'' species form an endosymbiont, endosymbiotic nitrogen fixation, nitrogen-fixing association with roots of (primarily) legumes and other fl ...

'' Rozahon ''et al''. 2014 * "'' Rhizobium populisoli''" Shen et al. 2021 * ''

Rhizobium puerariae ''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 ...

'' Boonsnongcheep ''et al''. 2016 * "'' Rhizobium qilianshanense''" Xu ''et al''. 2013 * "''

Rhizobium quercicola ''Rhizobium'' is a genus of Gram-negative soil bacteria that nitrogen fixation, fix nitrogen. ''Rhizobium'' species form an endosymbiont, endosymbiotic nitrogen fixation, nitrogen-fixing association with roots of (primarily) legumes and other fl ...

''" Wang et al. 2022 * "'' Rhizobium redzepovicii''" Rajnovic et al. 2022 * ''

Rhizobium rhizogenes ''Rhizobium rhizogenes'' (formerly ''Agrobacterium rhizogenes'') is a Gram-negative soil bacterium that produces hairy root disease in dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched adventitious ...

'' (Riker ''et al''. 1930) Young ''et al''. 2001 * "'' Rhizobium rhizolycopersici''" Thin ''et al''. 2021 * '' Rhizobium rhizoryzae'' Zhang ''et al''. 2014 * '' Rhizobium ruizarguesonis'' Jorrin ''et al''. 2020 * '' Rhizobium smilacinae'' Zhang ''et al''. 2014 * '' Rhizobium soli'' Yoon ''et al''. 2010 * '' Rhizobium sophorae'' Jiao ''et al''. 2014 * '' Rhizobium sophoriradicis'' Jiao ''et al''. 2014 * '' Rhizobium straminoryzae'' Lin ''et al''. 2014 * ''

Rhizobium sullae ''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 ...

'' Squartini ''et al''. 2002 * "'' Rhizobium terrae''" Ruan ''et al''. 2020 * '' Rhizobium tibeticum'' Hou ''et al''. 2009 * '' Rhizobium tropici'' Martínez-Romero ''et al''. 1991 * '' Rhizobium tubonense'' Zhang ''et al''. 2011 * '' Rhizobium tumorigenes'' Kuzmanović ''et al''. 2019 * '' Rhizobium vallis'' Wang ''et al''. 2011 * '' Rhizobium viscosum'' (Gasdorf ''et al''. 1965) Flores-Félix ''et al''. 2017 * ''

Rhizobium wenxiniae ''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 ...

'' Gao ''et al''. 2017 * '' Rhizobium yanglingense'' Tan ''et al''. 2001 * ''

Rhizobium zeae ''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 ...

'' Celador-Lera ''et al''. 2017 Species in "parentheses" have been described, but not validated according to the

Bacteriological Code The International Code of Nomenclature of Prokaryotes (ICNP) formerly the International Code of Nomenclature of Bacteria (ICNB) or Bacteriological Code (BC) governs the scientific names for Bacteria and Archaea.P. H. A. Sneath, 2003. A short histor ...

Phylogeny

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

Notes

References

External links

Current research on ''Rhizobium leguminosarum''
at the

Norwich Research Park Norwich Research Park is a business community located to the southwest of Norwich, Norfolk, in East Anglia, England close to the A11 road (England), A11 and the A47 road, A47 roads. Set in over 230 hectares of parkland, Norwich Research Park i ...

Video and commentary on root nodules and Rhizobium in White Clover
{{Authority control Rhizobiaceae Bacteria genera