THE STRUCTURE OF A NOVEL POLYSACCHARIDE PRODUCED BY BRADYRHIZOBIUM SPECIES WITHIN SOYBEAN NODULES

Certain strains of Bradyrhizobium japonicum and B. elkanii produce a p olysaccharide within the root nodules of their legume host, soybean. T hese nodule polysaccharides (NPSs) were isolated and characterized. Th e NPS produced by B. elkanii strains proved to be identical in glycosy l composition and linkages to the extracellular polysaccharide (EPS) o f this species indicating that the NPS and EPS for B. elkanii have ide ntical structures (W.F. Dudman, Carbohydr. Res., 66 (1978) 9-23), [GRA PHICS] However, the structure of the NPS from B. japonicum proved to b e quite different from that of its EPS. Methylation analysis of this N PS showed that it consists of 3-linked Gal, 3-linked Rha, 2,4-linked R ha, 4-linked Rha, and terminal 2-O-methyl GlcA in a 1:1:1:1:1 ratio. S tereochemical configurations of the glycosyl residues were determined by the preparation and analysis of trimethylsilyl (Me(3)Si) (-)-2-buty l glycosides. NMR spectroscopy (both H-1 and C-13) showed that the Gal residue is alpha-linked, while all the other glycosyl residues are be ta-linked. Oligosaccharides produced by periodate oxidation-Smith degr adation were purified, as were oligosaccharides produced by partial ac id hydrolysis. Characterization of the Smith degradation products by m ethylation analysis, NMR spectroscopy, electrospray-mass spectrometry, and characterization of the partial acid hydrolysate oligosaccharides showed that the repeating oligosaccharide unit of the NPS has the str ucture, [GRAPHICS] CS]