Home > Taxonomy > Non rhizobia

Updated 14th September 2009

Bacteria that are not rhizobia

This page lists bacteria that could be confused with rhizobia. I define 'rhizobia' as "Bacteria capable of forming symbiotic root nodules on legumes", other definitions may differ. Naturally this is a continual work in progress. As well as the categories below there are many diverse species of bacteria that can fix nitrogen, but in a free living state - not in root nodules. A few examples of these are Rhodopseudomonas palustris, Azospirillum sp., Azotobacter sp. and many more. There are links on the left hand side of the page to 'official' bacteria nomenclature websites

Agrobacterium

The Agrobacterium have been renamed as Rhizobium species (Young et al. 2001), they are listed below, with their new names. See the LPSN for more information on the Agrobacterium. These generally do not form symbiotic root nodules, unless they harbour a Sym plasmid or other transposable element with nodulation genes. In this case, I would define them as rhizobia. Other Agrobacterium have been reclassified as Stappia, Ruegeria, and Pseudorhodobacter.

Reference: YOUNG (J.M.), KUYKENDALL (L.D.), MARTÍNEZ-ROMERO (E.), KERR (A.) and SAWADA (H.): A revision of Rhizobium Frank 1889, with an emended description of the genus, and the inclusion of all species of Agrobacterium Conn 1942 and Allorhizobium undicola de Lajudie et al. 1998 as new combinations: Rhizobium radiobacter, R. rhizogenes, R. rubi, R. undicola and R. vitis. Int. J. Syst. Evol. Microbiol., 2001, 51, 89-103. (Abstract)

Old name	New Name
Agrobacterium larrymoorei	Rhizobium larrymoorei
Agrobacterium radiobacter = Agrobacterium tumefaciens	Rhizobium radiobacter
Agrobacterium rhizogenes	Rhizobium rhizogenes
Agrobacterium rubi	Rhizobium rubi
Agrobacterium vitis	Rhizobium vitis

Bacteria that are not rhizobia in 'rhizobia genera'

These may have names that suggest that they are rhizobia, but have not been shown to form symbiotic root nodules.

Burkholderia unamae	N2 fixing but does not form root nodules
Bradyrhizobium betae	tumour forming bacteria
Mesorhizobium thiogangeticum	Sulfur oxidising, nodulation unknown
Rhizobium selenitireducens	selenite-reducing, isolated from bioreactor (invalid name was: R. selenireducens)
Rhizobium cellulosilyticum	unable to form nodules on tested legumes, but does have nodD (Garcia-Fraile et al, 2007)
Cohnella phaseoli	Isolated from nodules, but cannot form root nodules (Garcia-Fraile et al, 2008)

Names that have not been validly published or revoked

These include names that have been submitted to the NCBI database but not yet published, and names that were never formally published. It also includes some names that were vaild, but are no longer valid.

Rhizobium massiliae	not rhizobia, unpublished (link to NCBI)
Rhizobium arachis	not valid (link to NCBI)
Bradyrhizobium lupini	not valid (link to NCBI)
Blastobacter denitrificans	not valid name is now Bradyrhizobium denitrificans (link to NCBI)
Agrobacterium agile	not valid (link to NCBI)
Mesorhizobium alexandrii	not valid. Name is now Hoeflea alexandrii (link to NCBI)
Rhizobium taeanense	not valid (link to NCBI)
Rhizobium soli	not valid (link to NCBI)
Mesorhizobium aestuarii	not valid. Name is now Aliihoeflea aestuarii (link to NCBI)
Rhizobium trifolii	a later synonym of R. leguminosarum (IJSEM paper)