Bradyrhizobium nanningense sp. nov., Bradyrhizobium guangzhouense sp. nov. and Bradyrhizobium zhanjiangense sp. nov., isolated from effective nodules of peanut in Southeast China.

Nine slow-growing rhizobia isolated from effective nodules on peanut (Arachis hypogaea) were characterized to clarify the taxonomic status using a polyphasic approach. They were assigned to the genus Bradyrhizobium on the basis of 16S rRNA sequences. MLSA of concatenated glnII-recA-dnaK genes classified them into three species represented by CCBAU 53390, CCBAU 51670 and CCBAU 51778, which presented the closest similarity to B. guangxiense CCBAU 53363, B. guangdongense CCBAU 51649 and B. manausense BR 3351, B. vignae 7-2 and B. forestalis INPA 54B, respectively. The dDDH (digital DNA-DNA hybridization) and ANI (Average Nucleotide Identity) between the genomes of the three representative strains and type strains for the closest Bradyrhizobium species were less than 42.1% and 91.98%, respectively, below the threshold of species circumscription. Effective nodules could be induced on peanut and Lablab purpureus by all representative strains, while Vigna radiata formed effective nodules only with CCBAU 53390 and CCBAU 51778. Phenotypic characteristics including sole carbon sources and growth features supported the phylogenetic results. Based on the genotypic and phenotypic features, strains CCBAU 53390, CCBAU 51670 and CCBAU 51778 are designated the type strains of three novel species, for which the names Bradyrhizobium nanningense sp. nov., Bradyrhizobium guangzhouense sp. nov. and Bradyrhizobium zhanjiangense sp. nov. are proposed, respectively.