Bradyrhizobium forestalis sp nov., an efficient nitrogen-fixing bacterium isolated from nodules of forest legume species in the Amazon

Three strains of nitrogen-fixing bacteria isolated from nodules of Inga sp. (INPA54B(T)) and Swartzia sp. (INPA86A and INPA01-91A) in soils under native forest in the Brazilian Amazon were previously identified as belonging to the Bradyrhizobium genus. In this study, these strains were characterized using a polyphasic approach to establish their taxonomic position. The three strains shared more than 99.5% sequence similarity of the 16S rRNA gene with the type strains of five Bradyrhizobium species (B. japonicum USDA 6(T), B. liaoningense LMG 18230(T), B. ottawaense OO99(T), B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T)). However, multilocus sequence analysis of two (recA and glnII) or three (atpD, gyrB, and recA) housekeeping genes indicated that these three strains represent a new Bradyrhizobium species, which is closely related to B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T). DNA-DNA hybridization values between INPA54B(T) and B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T) were only 41.5 and 30.9%, respectively. Phenotypic characterization also allowed the differentiation of the novel species from B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T). In the phylogenetic analysis of the nodC and nifH genes, the three strains showed similar sequences that were divergent from those of type strains of all Bradyrhizobium species. We concluded that these strains represent a novel species, for which the name Bradyrhizobium forestalis is proposed, with INPA54B(T) (= LMG 10044(T)) as type strain. The G+C content in the DNA of INPA54B(T) is 63.7 mol%.