Bradyrhizobium centrosemae (symbiovar centrosemae) sp. nov., Bradyrhizobium americanum (symbiovar phaseolarum) sp. nov. and a new symbiovar (tropici) of Bradyrhizobium viridifuturi establish symbiosis with Centrosema species native to America

In this work we analyze through a polyphasic approach several Bradyrhizobium strains isolated in Venezuela from root nodules of Centrosema species. The analysis of the 16S rRNA gene showed that the strains belong to three clusters within genus Bradyrhizobium which have 100% similarity with Bradyrhizobium daqingense CCBAU 15774T Bradyrhizobium guangxiense CCBAU 53363T and Bradyrhizobium viridifuturi SEMIA 690T. The results of recA and glnII gene analysis confirmed the identification of the strains CMVU02 and CMVU30 as Bradyrhizobium viridifuturi but the nodC gene analysis showed that they belong to a new symbiovar for which we propose the name tropici. Nevertheless, the concatenated recA and glnII gene phylogenetic analysis, DNA–DNA hybridization and phenotypic characterization showed that the strains A9T, CMVU44T and CMVU04 belong to two novel Bradyrhizobium species. The analysis of the nodC gene showed that these strains also represent two new symbiovars. Based on these results we propose the classification of the strain A9T isolated from Centrosema molle into the novel species Bradyrhizobium centrosemae (sv. centrosemae) sp. nov. (type strain A9T = LMG 29515T = CECT 9095T). and the classification of the strains CMVU44T and CMVU04 isolated from C. macrocarpum into the novel species Bradyrhizobium americanum (sv. phaseolarum) sp. nov. (type strain CMVU44T = LMG 29514T = CECT 9096T).