Comparison of Extracellular Polysaccharide Composition, Rhizobitoxine Production, and Hydrogenase Phenotype among Various Strains of Bradyrhizobium japonicum

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Abstract
A survey of 51 strains of Bradyrhizobium japonicum was performed with respect to the composition of extracellular polysaccharide (EPS), the production of rhizobitoxine and the hydrogenase phenotype. A good correlation was found among these three different characteristics. Thirty-six strains producing an EPS composed of glucose, mannose, galactose, 4-O-methyl galactose and galacturonic acid did not synthesize rhizobitoxine, whereas 14 strains producing an EPS composed of rhamnose and 4-O-methyl glucuronic acid were all found to synthesize rhizobitoxine. Hydrogen-uptake positive (Hup+) strains were confined exclusively to the former group of strains which produced an EPS composed of glucose, mannose, galactose, 4-O-methyl galactose and galacturonic acid. These results suggest that the phenotype with respect to rhizobitoxine production and hydrogen uptake is involved in the phylogeny of Bradyrhizobium japonicum as well as in the productivity of nodulated soybeans.