Rhizobium hidalgonense and Rhizobium redzepovicii as novel faba bean (Vicia faba) microsymbionts in Mexican soils

Abstract As a legume crop widely cultured in the world, faba bean ( Vicia faba L.) plants form root nodules with diverse Rhizobium species in different regions. But the symbionts associated with this plant in Mexico has not been studied although it has been cultured for more than 500 years in the country. To investigate the diversity and species-symbiovar affiliations of rhizobia associated with faba bean in Mexico, we isolated the rhizobia of this plant grown in Mexico. Based upon the analysis of recA gene phylogeny, two genotypes were distinguished among a total of 35 isolates, and they were identified as Rhizobium hidalgonense and Rhizobium redzepovicii , respectively, by the whole genomic sequence analysis. Both the species harbored identical nod gene cluster and the same phylogenetic positions of nodC and nifH . So, all of them were identified into the symbiovar viciae. R. hidalgonense was only isolated from slightly acid soil and R. redzepvicii was found in acid and neutral soils in this study. The community composition of rhizobia associated with faba bean in Mexico was unique since these two Rhizobium species previously reported as symbionts of common bean. As conclusion, faba bean rhizobia in Mexico formed novel symbiovar, sv. viciae, in species R. hidalgonense and R. redzepovicii . These results added novel evidence about the co-evolution, diversification and biogeographic patterns of rhizobia in association with their host legumes in distinct geographic regions.