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

Abstract

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 %.

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