Bradyrhizobium pachyrhizi sp nov and Bradyrhizobium jicamae sp nov., isolated from effective nodules of Pachyrhizus erosus

Several strains isolated from the legume Pachyrhizus erosus were characterized on the basis of diverse genetic, phenotypic and symbiotic approaches. These novel strains formed two groups closely related to Bradyrhizobium elkanii according to their 16S rRNA gene sequences. Strains PAC48(T) and PAC68(T), designated as the type strains of these two groups, presented 99.8 and 99.1 % similarity, respectively, in their 16S rRNA gene sequences with respect to B. elkanii USDA 76(T). In spite of these high similarity values, the analysis of additional phylogenetic markers such as atpD and glnll genes and the 16S-23S intergenic spacer (ITS) showed that strains PAC48(T) and PAC68(T) represented two separate novel species of the genus Bradyrhizobium with B. elkanii as their closest relative. Phenotypic differences among the novel strains isolated from Pachyrhizus and B. elkanii were found regarding the assimilation of carbon sources and antibiotic resistance. All these differences were congruent with DNA-DNA hybridization analysis which revealed 21 % genetic relatedness between strains PAC48(T) and PAC68(T) and 46 % and 25 %, respectively, between these strains and B. elkanii LMG 6134(T). The nodD and nifH genes of strains PAC48(T) and PAC68(T) were phylogenetically divergent from those of bradyrhizobia species that nodulate soybean. Soybean was not nodulated by the novel Pachyrhizus isolates. Based on the genotypic and phenotypic data obtained in this study, the new strains represent two novel species for which the names Bradyrhizobium pachyrhizi sp. nov. (type strain PAC48(T) =LMG 24246(T) =CECT 7396(T)) and Bradyrhizobium jicamae sp. nov. (type strain PAC68(T) =LMG 24556(T) =CECT 7395(T)) are proposed.