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

Abstract

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 15774(T)Bradyrhizobium guangxiense CCBAU 53363(T) and Bradyrhizobium viridifuturi SEMIA 690(T). 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 A9(T), CMVU44(T) 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 A9(T) isolated from Centrosema molle into the novel species Bradyrhizobium centrosemae (sv. centrosemae) sp. nov. (type strain A9(T)=LMG 29515(T)=CECT 9095(T)). and the classification of the strains CMVU44(T) and CMVU04 isolated from C. macrocarpum into the novel species Bradyrhizobium americanum (sv. phaseolarum) sp. nov. (type strain CMVU44(T)=LMG 29514(T)=CECT 9096(T)).

Keywords: Bradyrhizobium; Centrosema; Phylogeny; Symbiovar.