Bradyrhizobium ripae sp. nov., a nitrogen-fixing symbiont isolated from nodules of wild legumes in Namibia

Root-nodule bacteria were isolated from wild legumes growing in the Kavango region, Namibia. Using a polyphasic approach, four strains belonging to the genus Bradyrhizobium (WR4(T), WR87, T10 and T12) were further characterized to clarify the taxonomic status of this group. On the basis of 16S rRNA gene sequences, the four strains showed highest similarity to Bradyrhizobium elkanii USDA 76(T) (99.9 %), Bradyrhizobium pachyrhizi PAC48(T) (identical) and to Bradyrhizobium brasilense UFLA03-321(T) (identical). Multilocus sequence analysis of concatenated glnll-recA-gyrB-dnaK-rpoB sequences and comparison of the intergenic transcribed spacer (ITS) sequences confirmed that the novel group belongs to a distinct lineage of the genus Bradyrhizobium, with <96.7 % (MLSA) and 97.25 % (ITS) nucleotide identity with B. elkanii USDA 76(T). Results from the sequence-based analysis were validated by DNA-DNA hybridization experiments and suggested a novel species. Several phenotypic features including carbon compound utilization and growth characteristics supported the phylogenetic data, thus it is concluded that the strains represent a novel species, for which the name Bradyrhizobium ripae sp. nov. is proposed, with type strain WR4(T) [LMG 30283, DSM 105795, NTCCM 0019 (Windhoek)].