Synthesis of a Low-Molecular-Weight Form of Exopolysaccharide by Bradyrhizobium japonicum USDA 110

A novel extracellular low-molecular-weight polysaccharide was detected as a contaminant within extracellular cyclic β-1,6-β-1,3-glucan preparations from Bradyrhizobium japonicum USDA 110 cultures. Compositional analysis, methylation analysis, and nuclear magnetic resonance analysis revealed that this low-molecular-weight polysaccharide was composed of the same pentasaccharide repeating unit previously described for the high-molecular-weight form of the exopolysaccharide (EPS) synthesized by B. japonicum strains. Mass spectrometry analysis indicated that the size of this low-molecular-weight form of EPS was consistent with a dimeric form of the pentasaccharide repeating unit.