''Rhizobium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

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

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

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

endosymbiotic An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), which live in the root ...

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

association with roots of (primarily)

legumes Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consu ...

and other flowering plants. The bacteria colonize plant cells to form

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 ...

s, where they convert atmospheric nitrogen into

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

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 ...

. The ammonia is shared with the host plant in the form of 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. The plant, in turn, provides the bacteria with

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s made by

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

. 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. I ...

, of which the genus ''Rhizobium'' is a typical example. ''Rhizobium'' is also capable of solubilizing phosphate.

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 co-discovery of viruses A virus i ...

was the first to isolate and cultivate a

microorganism A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...

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. The

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 ...

is conducting research involving 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 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'' 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 ''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 ''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 ...

'' 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'' 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'' 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'' 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'' 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'' 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'' 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'' Dangeard 1926 (Approved Lists 1980) * "'' Rhizobium phenanthrenilyticum''" Wen ''et al''. 2011 * ''

Rhizobium pisi ''Rhizobium pisi'' 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 a ...

'' 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 Dicotyledon, dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched ...

'' (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'' 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'' 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 The International Code of Nomenclature of Prokaryotes (ICNP) or Prokaryotic Code, 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 ...

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 naming and taxonomy of prokaryotes, following the taxonomy requirements and rulings of the International Code of Nomenclatu ...

(LPSN). The phylogeny is based on whole-genome analysis.

Notes

References

External links

Current research on nitrogen fixation by rhizobia
at the

Norwich Research Park Norwich Research Park (NRP) is a science park, science research park located to the southwest of Norwich in East Anglia close to the A11 road (England), A11 and the A47 road, A47 roads. Set in a area of parkland, it is one of five Biotechnolog ...

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