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. 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. Rhizobium is also capable of solubilizing phosphate.

History

Martinus Beijerinck was the first to isolate and cultivate a microorganism 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

Some 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.

Rhizobium rhizogenes is a pathogenic species of Rhizobium that causes hairy root disease by injecting a root-inducing T-DNA into the plants. It produces industrially-useful hairy root cultures as well as genetically modified plants.

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 <small>Román-Ponce et al. 2016</small>
  • Rhizobium aegyptiacum <small>Shamseldin et al. 2016</small>
  • Rhizobium aethiopicum <small>Aserse et al. 2017</small>

<!-- Rhizobium aggregatum was reclassified as Peteryoungia aggregata. -->

  • Rhizobium alamii <small>Berge et al. 2009</small>
  • "Rhizobium album" <small>Hang et al. 2019</small>
  • "Rhizobium albus" <small>Li et al. 2017</small>

<!-- Rhizobium alkalisoli was renamed Neorhizobium alkalisoli. -->

  • Rhizobium altiplani <small>Baraúna et al. 2016</small>
  • Rhizobium alvei <small>Sheu et al. 2015</small>
  • Rhizobium anhuiense <small>Zhang et al. 2015</small>
  • Rhizobium aquaticum <small>Máthé et al. 2019</small>
  • "Rhizobium arachis" <small>Wang et al. 2001</small>
  • Rhizobium arenae <small>Zhang et al. 2017</small>
  • Rhizobium arsenicireducens <small>Mohapatra et al. 2020</small>

<!-- Rhizobium azibium was renamed Rhizobium azibense, which was reclassified as Rhizobium gallicum. -->

<!-- Rhizobium azibense was reclassified as Rhizobium gallicum. -->

  • Rhizobium azooxidifex <small>Behrendt et al. 2016</small>
  • Rhizobium bangladeshense <small>Rashid et al. 2015</small>
  • Rhizobium binae <small>Rashid et al. 2015</small>

<!-- Rhizobium borbori was renamed Allorhizobium borbori. -->

  • Rhizobium calliandrae <small>Rincón-Rosales et al. 2013</small>
  • Rhizobium capsici <small>Lin et al. 2015</small>
  • Rhizobium cauense <small>Liu et al. 2015</small>
  • Rhizobium cellulosilyticum <small>García-Fraile et al. 2007</small>
  • Rhizobium changzhiense <small>Zhang et al. 2021</small>
  • Rhizobium chutanense <small>Huo et al. 2019</small>

<!-- Rhizobium ciceri was renamed Mesorhizobium ciceri. -->

  • "Rhizobium cremeum" <small>Yang et al. 2022</small>
  • "Rhizobium croatiense" <small>Rajnovic et al. 2022</small>

<!-- Rhizobium daejeonense was renamed Ciceribacter daejeonensis. -->

  • "Rhizobium deserti" <small>Liu et al. 2020</small>
  • Rhizobium dioscoreae <small>Ouyabe et al. 2020</small>
  • Rhizobium ecuadorense <small>Ribeiro et al. 2015</small>

<!-- Rhizobium endolithicum was reclassified as Pseudorhizobium endolithicum. -->

  • Rhizobium endophyticum <small>López-López et al. 2010</small>
  • Rhizobium esperanzae <small>Cordeiro et al. 2017</small>
  • Rhizobium etli <small>Segovia et al. 1993</small>

<!-- Rhizobium fabae was reclassified as Rhizobium pisi. -->

  • Rhizobium favelukesii <small>Torres Tejerizo et al. 2016</small>
  • "Rhizobium flavescens" <small>Su et al. 2021</small>

<!-- Rhizobium flavum was reclassified as Pseudorhizobium flavum. -->

<!-- Rhizobium fredii was renamed Ensifer fredii. -->

  • Rhizobium freirei <small>Dall'Agnol et al. 2013</small>

<!-- Rhizobium galegae was renamed Neorhizobium galegae. -->

  • Rhizobium gallicum <small>Amarger et al. 1997</small>
  • Rhizobium gei <small>Shi et al. 2016</small>

<!-- Rhizobium giardinii was renamed Pararhizobium giardinii. -->

  • "Rhizobium glycinendophyticum" <small>Wang et al. 2020</small>
  • Rhizobium grahamii <small>López-López et al. 2011</small>
  • Rhizobium hainanense <small>Chen et al. 1997</small>
  • Rhizobium halophytocola <small>Bibi et al. 2012</small>
  • "Rhizobium halotolerans" <small>Diange and Lee 2013</small>
  • "Rhizobium hedysari" <small>Casella et al. 1986</small>
  • "Rhizobium hedysari" <small>Xu et al. 2017</small>
  • "Rhizobium hedysarum" <small>Casella et al. 1984</small>

<!-- Rhizobium helanshanense was renamed Pararhizobium helanshanense. -->

  • Rhizobium helianthi <small>Wei et al. 2015</small>

<!-- Rhizobium herbae was renamed Pararhizobium herbae. -->

  • Rhizobium hidalgonense <small>Yan et al. 2020</small>

<!-- Rhizobium huakuii was renamed Mesorhizobium huakuii. -->

<!-- Rhizobium huautlense was renamed Neorhizobium huautlense. -->

  • "Rhizobium indicum" <small>Rahi et al. 2020</small>
  • Rhizobium indigoferae <small>Wei et al. 2002</small>

<!-- Rhizobium ipomoeae was reclassified as Peteryoungia ipomoeae. -->

  • Rhizobium jaguaris <small>Rincón-Rosales et al. 2013</small>

<!-- Rhizobium japonicum was renamed Bradyrhizobium japonicum. -->

  • "Rhizobium kunmingense" <small>Shen et al. 2010</small>
  • Rhizobium laguerreae <small>Saïdi et al. 2014</small>

<!-- Rhizobium larrymoorei was renamed Agrobacterium larrymoorei. -->

  • Rhizobium leguminosarum <small>(Frank 1879) Frank 1889 (Approved Lists 1980)</small>
  • Rhizobium lemnae <small>Kittiwongwattana & Thawai 2014</small>
  • Rhizobium lentis <small>Rashid et al. 2015</small>
  • Rhizobium leucaenae <small>Ribeiro et al. 2011</small>

<!-- Rhizobium loessense was reclassified as Mesorhizobium mongolense. -->

<!-- Rhizobium loti was renamed Mesorhizobium loti. -->

<!-- Rhizobium lupini was renamed Bradyrhizobium lupini. -->

  • Rhizobium lusitanum <small>Valverde et al. 2006</small>

<!-- Rhizobium marinum was reclassified as Pseudorhizobium marinum. -->

<!-- "Candidatus Rhizobium massiliae" is a misspelling of "Candidatus Rhizobium massiliense". -->

  • "Candidatus Rhizobium massiliense" <small>Greub et al. 2004.</small>
  • Rhizobium mayense <small>Rincón-Rosales et al. 2013</small>

<!-- Rhizobium mediterraneum was renamed Mesorhizobium mediterraneum. -->

<!-- Rhizobium meliloti was renamed Ensifer meliloti. -->

  • Rhizobium mesoamericanum <small>López-López et al. 2011</small>
  • Rhizobium mesosinicum <small>Lin et al. 2009</small>
  • Rhizobium metallidurans <small>Grison et al. 2015</small>
  • Rhizobium miluonense <small>Gu et al. 2008</small>
  • Rhizobium mongolense <small>van Berkum et al. 1998</small>
  • Rhizobium multihospitium <small>Han et al. 2008</small>

<!-- Rhizobium naphthalenivorans was renamed Ciceribacter naphthalenivorans. -->

<!-- Rhizobium nepotum was renamed Agrobacterium nepotum. -->

<!-- Rhizobium oryzae was renamed Xaviernesmea oryzae. -->

  • Rhizobium oryzicola <small>Zhang et al. 2015</small>
  • "Rhizobium oryzihabitans" <small>Zhao et al. 2020</small>

<!-- Rhizobium oryziradicis was renamed Allorhizobium oryziradicis. -->

  • Rhizobium pakistanense <small>corrig. Khalid et al. 2015</small>

<!-- Rhizobium pakistanensis is a misspelling of Rhizobium pakistanense. -->

<!-- Rhizobium paknamense was renamed Allorhizobium paknamense. -->

  • "Rhizobium panacihumi" <small>Kang et al. 2019</small>
  • Rhizobium paranaense <small>Dall'Agnol et al. 2014</small>

<!-- Rhizobium petrolearium was renamed Neorhizobium petrolearium. -->

  • Rhizobium phaseoli <small>Dangeard 1926 (Approved Lists 1980)</small>
  • "Rhizobium phenanthrenilyticum" <small>Wen et al. 2011</small>
  • Rhizobium pisi <small>Ramírez-Bahena et al. 2008</small>
  • "Rhizobium pongamiae" <small>Kesari et al. 2013</small>
  • Rhizobium populi <small>Rozahon et al. 2014</small>
  • "Rhizobium populisoli" <small>Shen et al. 2021</small>

<!-- Rhizobium pseudoryzae was renamed Allorhizobium pseudoryzae. -->

  • Rhizobium puerariae <small>Boonsnongcheep et al. 2016</small>

<!-- Rhizobium pusense was renamed Agrobacterium pusense. -->

  • "Rhizobium qilianshanense" <small>Xu et al. 2013</small>
  • "Rhizobium quercicola" <small>Wang et al. 2022</small>

<!--Rhizobium radiobacter was renamed Agrobacterium radiobacter. -->

  • "Rhizobium redzepovicii" <small>Rajnovic et al. 2022</small>
  • Rhizobium rhizogenes <small>(Riker et al. 1930) Young et al. 2001</small>
  • "Rhizobium rhizolycopersici" <small>Thin et al. 2021</small>

<!-- Rhizobium rhizophilum was reclassified as Peteryoungia rhizophila. -->

  • Rhizobium rhizoryzae <small>Zhang et al. 2014</small>

<!-- Rhizobium rhizosphaerae was renamed Xaviernesmea rhizosphaerae. -->

<!-- Rhizobium rosettiformans was reclassified as Peteryoungia rosettiformans. -->

<!-- Rhizobium rubi was renamed Agrobacterium rubi. -->

  • Rhizobium ruizarguesonis <small>Jorrin et al. 2020</small>

<!-- Rhizobium selenireducens is a misspelling of Rhizobium selenitireducens, which was renamed Ciceribacter selenitireducens. -->

<!-- Rhizobium selenitireducens was renamed Ciceribacter selenitireducens. -->

<!-- Rhizobium skierniewicense was renamed Agrobacterium skierniewicense. -->

  • Rhizobium smilacinae <small>Zhang et al. 2014</small>
  • Rhizobium soli <small>Yoon et al. 2010</small>
  • Rhizobium sophorae <small>Jiao et al. 2014</small>
  • Rhizobium sophoriradicis <small>Jiao et al. 2014</small>

<!-- Rhizobium sphaerophysae was renamed Pararhizobium sphaerophysae. -->

  • Rhizobium straminoryzae <small>Lin et al. 2014</small>

<!-- Rhizobium subbaraonis was renamed Mycoplana subbaraonis. -->

  • Rhizobium sullae <small>Squartini et al. 2002</small>

<!-- Rhizobium taibaishanense was renamed Allorhizobium taibaishanense. -->

<!-- Rhizobium tarimense was reclassified as Pseudorhizobium tarimense. -->

  • "Rhizobium terrae" <small>Ruan et al. 2020</small>

<!-- Rhizobium tianshanense was renamed Mesorhizobium tianshanense. -->

  • Rhizobium tibeticum <small>Hou et al. 2009</small>

<!-- Rhizobium trifolii was reclassified as Rhizobium leguminosarum. -->

  • Rhizobium tropici <small>Martínez-Romero et al. 1991</small>
  • Rhizobium tubonense <small>Zhang et al. 2011</small>
  • Rhizobium tumorigenes <small>Kuzmanović et al. 2019</small>

<!-- Rhizobium undicola was renamed Allorhizobium undicola. -->

  • Rhizobium vallis <small>Wang et al. 2011</small>

<!-- Rhizobium vignae was renamed Neorhizobium vignae. -->

  • Rhizobium viscosum <small>(Gasdorf et al. 1965) Flores-Félix et al. 2017</small>

<!-- Rhizobium vitis was renamed Allorhizobium vitis. -->

  • Rhizobium wenxiniae <small>Gao et al. 2017</small>

<!-- Rhizobium wuzhouense was reclassified as Peteryoungia wuzhouensis. -->

  • Rhizobium yanglingense <small>Tan et al. 2001</small>

<!-- Rhizobium yantingense was reclassified as Endobacterium yantingense. -->

  • Rhizobium zeae <small>Celador-Lera et al. 2017</small>

Species in "double quotes" have been described, but not validated according to the Bacteriological Code.

Notes

References

  • Current research on nitrogen fixation by rhizobia at the Norwich Research Park
  • Video and commentary on root nodules and Rhizobium in White Clover