Ensifer (often referred to in literature by its synonym Sinorhizobium) is a genus of nitrogen-fixing bacteria (rhizobia), three of which (Ensifer meliloti,^[22][23] Ensifer medicae^[24] and Ensifer fredii^[25][26]) have been sequenced.

Quick Facts Ensifer, Scientific classification ...

Ensifer
Ensifer fredii USDA257 on an agar plate of typtone-yeast extract agar.
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Alphaproteobacteria
Order:	Hyphomicrobiales
Family:	Rhizobiaceae
Genus:	Ensifer Casida, 1982
Type species
Ensifer adhaerens Casida, 1982
Species[1][2][3][4]
"Sinorhizobium abri" Ogasawara et al. 2003[5][6] Ensifer adhaerens Casida 1982[7] Ensifer alkalisoli Li et al. 2016 Ensifer americanus corrig. (Toledo et al. 2004) Wang et al. 2015[8] Ensifer arboris (Nick et al. 1999) Young 2003[9] "Ensifer aridi" Le Quéré et al. 2017[10][6] "Ensifer aridi" Rocha et al. 2020[11][6] "Sinorhizobium chiapanecum" Rincón-Rosales et al. 2009[12] "Ensifer collicola" Jang et al. 2017[6] Ensifer fredii (Scholla and Elkan 1984) Young 2003[13] Ensifer garamanticus Merabet et al. 2010[14] Ensifer glycinis Yan et al. 2016[15] "Sinorhizobium indiaense" Ogasawara et al. 2003[5][6] Ensifer kostiensis (Nick et al. 1999) Young 2003[9] Ensifer kummerowiae (Wei et al. 2002) Young 2003[16] Ensifer medicae (Rome et al. 1996) Young 2003[17] Ensifer meliloti (Dangeard 1926) Young 2003[18] Ensifer mexicanus Lloret et al. 2007[19] Ensifer morelensis corrig. (Wang et al. 2002) Wang et al. 2015 Ensifer numidicus Merabet et al. 2010[14] Ensifer psoraleae Wang et al. 2013[20] Ensifer saheli (De Lajudie et al. 1994) Young 2003[18] symbiovar acaciae symbiovar sesbaniae Ensifer sesbaniae Wang et al. 2015[20] Ensifer shofinae Chen et al. 2017 Ensifer sojae Li et al. 2011[21] Ensifer terangae (De Lajudie et al. 1994) Young 2003[18] symbiovar acaciae symbiovar sesbaniae
Synonyms[2]
Sinorhizobium Chen et al. 1988

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The generic epithet Ensifer derives from the Latin noun ensifer, "sword-bearer".^[7] The synonym Sinorhizobium is a combination of Medieval Latin noun sino ("China"), the Classical Greek noun rhiza ("root"), and the Classical Greek noun bium ("life"). Thus, the Neo-Latin generic epithet of the synonym Sinorhizobium means "a Rhizobium isolated from China", in turn referring to the related genus Rhizobium ("root-associated life form").^[1][13]

The name Ensifer was published in 1982 and the name Sinorhizobium was published in 1988 thus the latter is regarded as a later synonym and by the rules of the Bacteriological Code (1990 Revision) of the International Committee on Systematics of Prokaryotes (ICSP), the older name (Ensifer) takes priority.^[27] In response to a request that the single extant species of Ensifer (Ensifer adhaerens) be moved to Sinorhizobium, a special ICSP subcommittee was formed to evaluate the request. It was ultimately ruled that Ensifer retained priority and that all Sinorhizobium species be transferred to the genus Ensifer.^[28][29] However, both terms continue to be used in published scientific literature, with Sinorhizobium being the more common.^[30]

Two species have been described which have since been reclassified into existing species: Sinorhizobium morelense (now Ensifer adhaerens)^[27][31] and Sinorhizobium xinjiangense (now Ensifer fredii^[32][33]—though some dissent exists^[20][34]).

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN).^[1][2] The following phylogeny is based on whole-genome analysis.^[35]

This phylogeny is based on a constrained analysis of the 16S ribosomal RNA.^[35]