Diversity of exopolysaccharide cluster I in the Bradyrhizobium genus

Bradyrhizobium , the largest rhizobial genus, is characterized by variety exopolysaccharides (EPSs) components, depending on the species. However, several genes involved in EPS synthesis remain unknown. In this study, we investigated whether 186 Bradyrhizobium strains possess EPS cluster I, which is involved in the synthesis of a pentasaccharide EPS by B. diazoefficiense USDA110. Homologous genes involved in EPS synthesis were found to be absent in the B. elkanii and Photosynthetic Bradyrhizobium supergroups, other than the B. japonicus supergroup. These findings suggest that genes related to EPS synthesis are yet to be identified in the B. elkanii and Photosynthetic Bradyrhizobium supergroups.