Bradyrhizobium brasilense sp nov., a symbiotic nitrogen-fixing bacterium isolated from Brazilian tropical soils

Four strains of rhizobia isolated from nodules of Vigna unguiculata (UFLA03-321(T), UFLA03-320 and UFLA03-290) and Macroptilium atropurpureum (UFLA04-0212) in Brazilian soils were previously reported as a new group within the genus Bradyrhizobium. To determine their taxonomic position, these strains were characterized in this study using a polyphasic approach. The analysis of the 16S rRNA gene grouped the four strains with Bradyrhizobium pachyrhizi PAC48(T). However, the concatenated sequence analysis of the two (recA and glnII) or three (atpD, gyrB and recA) housekeeping genes indicated that these strains represent a novel species of Bradyrhizobium, which is very closely related to B. pachyrhizi PAC48(T) and B. elkanii USDA 76(T). Genomic relatedness analyses between the UFLA03-321(T) strain and B. elkanii USDA 76(T) and B. pachyrhizi PAC48(T) revealed an average nucleotide identity below 96% and values of estimated DNA-DNA hybridization below 70%, confirming that they represent genomically distinct species. Analysis of MALDI-TOF MS (Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry) profiles and phenotypic characteristics also allowed differentiation of the novel species from its two neighboring species. In phylogenetic analysis of nodC and nifH genes, UFLA03-321(T) exhibited maximum similarity with B. tropiciagri CNPSo 1112(T). The data suggest that these four UFLA strains represent a novel species, for which the name Bradyrhizobium brasilense sp. nov. is proposed, with UFLA03-321(T) (=LMG 29353 =CBAS645) as type strain. G + C content in the DNA of UFLA03-321(T) is 63.9 mol %.