Determination of the chemical structure of the capsular polysaccharide of strain B33, a fast-growing soya bean-nodulating bacterium isolated from an arid region of China

We have determined the structure of a polysaccharide from strain B33, a fas t-growing bacterium that forms nitrogen-fixing nodules with Asiatic and Ame rican soya bean cultivars. On the basis of monosaccharide analysis, methyla tion analysis, one-dimensional H-1- and C-13-NMR and two-dimensional NMR ex periments, the structure was shown to consist of a polymer having the repea ting unit --> 6)-4-O-methyl-alpha -D-Glcp-(1 -->4)-3-O-methyl- beta -D-Glcp A-(1 --> (where GlcpA is glucopyranuronic acid and Glcp is glucopyranose). Strain B33 produces a K-antigen polysaccharide repeating unit that does not have the structural motif sugar-Kdx [where Kdx is 3-deoxy-D-manno-2-octulo sonic acid (Kdo) or a Kdo-related acid] proposed for different Sinorhizobiu m fredii strains, all of them being effective with Asiatic soya bean cultiv ars but unable to form nitrogen-fixing nodules with American soya bean cult ivars. Instead, it resembles the K-antigen of S. fredii strain HH303 (rhamn ose, galacturonic acid), which is also effective with both groups of soya b ean cultivars. Only the capsular polysaccharide from strains B33 and HH303 have monosaccharide components that are also present in the surface polysac charide of Bradyrhizobium elkanii strains, which consists of a 4-O-methyl-D -glucurono-L-rhamnan.