''Rhizobium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

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 wa ...

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 ...

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 am ...

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

endosymbiotic An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...

nitrogen-fixing 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 for ...

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 ...

using the enzyme

nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...

and then provide organic nitrogenous compounds such as

glutamine Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...

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. Th ...

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 in ...

. 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 g ...

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

History

Martinus Beijerinck Martinus Willem Beijerinck (, 16 March 1851 – 1 January 1931) was a Dutch microbiologist and botanist who was one of the founders of virology and environmental microbiology. He is credited with the discovery of viruses, which he called "'' ...

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 old ...

from the nodules of legumes in 1888. He named it ''Bacillus radicicola'', which is now placed in '' Bergey's Manual of Determinative Bacteriology'' 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 sepa ...

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 ''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 ...

'' Román-Ponce ''et al''. 2016 * ''

Rhizobium aegyptiacum ''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 ...

'' Shamseldin ''et al''. 2016 * ''

Rhizobium aethiopicum ''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 ...

'' Aserse ''et al''. 2017 * ''

Rhizobium alamii ''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 ...

'' Berge ''et al''. 2009 * "''

Rhizobium album ''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 ...

''" Hang ''et al''. 2019 * "''

Rhizobium albus ''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 ...

''" Li ''et al''. 2017 * ''

Rhizobium altiplani ''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 ...

'' Baraúna ''et al''. 2016 * ''

Rhizobium alvei ''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 ...

'' Sheu ''et al''. 2015 * '' Rhizobium anhuiense'' Zhang ''et al''. 2015 * '' Rhizobium aquaticum'' Máthé ''et al''. 2019 * "'' Rhizobium arachis''" Wang et al. 2001 * '' Rhizobium arenae'' Zhang ''et al''. 2017 * '' Rhizobium arsenicireducens'' Mohapatra ''et al''. 2020 * '' Rhizobium azooxidifex'' Behrendt ''et al''. 2016 * ''

Rhizobium bangladeshense ''Rhizobium bangladeshense'' is a gram-negative bacterium which was isolated from root nodules of lentils in Bangladesh. Description ''Rhizobium bangladeshense'' are rod-shaped bacteria which live in soil, particularly on the root nodules of p ...

'' Rashid ''et al''. 2015 * '' Rhizobium binae'' Rashid ''et al''. 2015 * '' Rhizobium calliandrae'' Rincón-Rosales ''et al''. 2013 * '' Rhizobium capsici'' Lin ''et al''. 2015 * '' Rhizobium cauense'' Liu ''et al''. 2015 * ''

Rhizobium cellulosilyticum ''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 ...

'' 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 ''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 ...

'' Cordeiro ''et al''. 2017 * ''

Rhizobium etli ''Rhizobium etli'' is a Gram-negative root-nodule bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorg ...

'' 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 ''Rhizobium gallicum'' is a Gram-negative root-nodule bacterium. It forms nitrogen-fixing root nodules on legumes, being first isolated from those of ''Phaseolus vulgaris ''Phaseolus vulgaris'', the common bean, is a herbaceous annual plan ...

'' 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''" 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''" Diange and Lee 2013 * "'' Rhizobium hedysari''" Casella ''et al.'' 1986 * "'' Rhizobium hedysari''" Xu ''et al''. 2017 * "'' Rhizobium hedysarum''" Casella et al. 1984 * ''

Rhizobium helianthi ''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 ...

'' Wei ''et al''. 2015 * '' Rhizobium hidalgonense'' Yan ''et al''. 2020 * "'' Rhizobium indicum''" Rahi ''et al''. 2020 * '' Rhizobium indigoferae'' 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'' (Frank 1879) Frank 1889 (Approved Lists 1980) * ''

Rhizobium lemnae ''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 ...

'' Kittiwongwattana & Thawai 2014 * '' Rhizobium lentis'' Rashid ''et al''. 2015 * '' Rhizobium leucaenae'' Ribeiro ''et al''. 2011 * '' Rhizobium lusitanum'' Valverde ''et al''. 2006 * "''Candidatus'' Rhizobium massiliense" Greub ''et al''. 2004. * '' Rhizobium mayense'' Rincón-Rosales ''et al''. 2013 * ''

Rhizobium mesoamericanum ''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 ...

'' 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'' Zhang ''et al''. 2015 * "'' Rhizobium oryzihabitans''" Zhao ''et al''. 2020 * '' Rhizobium pakistanense'' corrig. Khalid ''et al''. 2015 * "'' Rhizobium panacihumi''" Kang ''et al''. 2019 * '' Rhizobium paranaense'' Dall'Agnol ''et al''. 2014 * ''

Rhizobium phaseoli ''Rhizobium phaseoli'' is a 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 ...

'' Dangeard 1926 (Approved Lists 1980) * "'' Rhizobium phenanthrenilyticum''" Wen ''et al''. 2011 * '' Rhizobium pisi'' Ramírez-Bahena ''et al''. 2008 * "'' Rhizobium pongamiae''" Kesari ''et al''. 2013 * '' Rhizobium populi'' Rozahon ''et al''. 2014 * "'' Rhizobium populisoli''" Shen et al. 2021 * '' Rhizobium puerariae'' Boonsnongcheep ''et al''. 2016 * "'' Rhizobium qilianshanense''" Xu ''et al''. 2013 * "'' Rhizobium quercicola''" 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'' Squartini ''et al''. 2002 * "'' Rhizobium terrae''" Ruan ''et al''. 2020 * '' Rhizobium tibeticum'' Hou ''et al''. 2009 * ''

Rhizobium tropici ''Rhizobium tropici'' is a 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 ...

'' Martínez-Romero ''et al''. 1991 * '' Rhizobium tubonense'' Zhang ''et al''. 2011 * ''

Rhizobium tumorigenes ''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 ...

'' Kuzmanović ''et al''. 2019 * '' Rhizobium vallis'' Wang ''et al''. 2011 * '' Rhizobium viscosum'' (Gasdorf ''et al''. 1965) Flores-Félix ''et al''. 2017 * '' Rhizobium wenxiniae'' Gao ''et al''. 2017 * '' Rhizobium yanglingense'' Tan ''et al''. 2001 * '' Rhizobium zeae'' Celador-Lera ''et al''. 2017 Species in "parentheses" have been described, but not validated according to the Bacteriological Code.

Phylogeny

The currently accepted taxonomy is based on the

List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature (LPSN) is an online database that maintains information on the nomenclature, naming and Taxonomy (biology), taxonomy of prokaryotes, following the taxonomy requirements and rulings of the In ...

(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 and the A47 roads. Set in over 230 hectares of parkland, Norwich Research Park is home to over 12,000 people ...

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