Bradyrhizobium cenepequi sp. nov., Bradyrhizobium semiaridum sp. nov., Bradyrhizobium hereditatis sp. nov. and Bradyrhizobium australafricanum sp. nov., symbionts of different leguminous plants of Western Australia and South Africa and definition of three novel symbiovars

Bradyrhizobium is a heterogeneous bacterial genus capable of establishing symbiotic associations with a broad range of legume hosts, including species of economic and environmental importance. This study was focused on the taxonomic and symbiovar definition of four strains - CNPSo 4026(T), WSM 1704(T), WSM 1738(T) and WSM 4400(T) - previously isolated from nodules of legumes in Western Australia and South Africa. The 16S rRNA gene phylogenetic tree allocated the strains to the Bradyrhizobium elkanii supergroup. The multilocus sequence analysis (MLSA) with partial sequences of six housekeeping genes - atpD, dnaK, glnII, gyrB, recA and rpoB - did not cluster the strains under study as conspecific to any described Bradyrhizobium species. Average nucleotide identity and digital DNA-DNA hybridization values were calculated for the four strains of this study and the closest species according to the MLSA phylogeny with the highest values being 95.46 and 62.20%, respectively; therefore, both being lower than the species delineation cut-off values. The nodC and nifH phylogenies included strains WSM 1738(T) and WSM 4400(T) in the symbiovars retamae and vignae respectively, and also allowed the definition of three new symbiovars, sv. cenepequi, sv. glycinis, and sv. cajani. Analysis of morphophysiological characterization reinforced the identification of four novel proposed Bradyrhizobium species that are accordingly named as follows: Bradyrhizobium cenepequi sp. nov. (CNPSo 4026(T)=WSM 4798(T)=LMG 31653(T)), isolated from Vigna unguiculata; Bradyrhizobium semiaridum sp. nov. (WSM 1704(T)=CNPSo 4028(T)=LMG 31654(T)), isolated from Tephrosia gardneri; Bradyrhizobium hereditatis sp. nov. (WSM 1738(T)=CNPSo 4025(T)=LMG 31652(T)), isolated from Indigofera sp.; and Bradyrhizobium australafricanum sp. nov. (WSM 4400(T)=CNPSo 4015(T)=LMG 31648(T)) isolated from Glycine sp.