Fractionation of the β-Linked Glucans of Bradyrhizobium japonicum and Their Response to Osmotic Potential

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Abstract
Bradyrhizobium japonicum USDA 110 synthesized both extracellular and periplasmic polysaccharides when grown on mannitol minimal medium. The extracellular polysaccharides were separated into a high-molecular-weight acidic capsular extracellular polysaccharide fraction (90% of total hexose) and three lower-molecular-weight glucan fractions by liquid chromatography. Periplasmic glucans, extracted from washed cells with 1% trichloroacetic acid, gave a similar pattern on liquid chromatography. Linkage analysis of the major periplasmic glucan fractions demonstrated mainly 6-linked glucose (63 to 68%), along with some 3,6- (8 to 18%), 3- (9 to 11%), and terminal (7 to 8%) linkages. The glucose residues were β-linked as shown by 1H-nuclear magnetic resonance analysis. Glucan synthesis by B. japonicum cells grown on mannitol medium with 0 to 350 mM fructose as osmolyte was measured. Fructose at 150 mM or higher inhibited synthesis of periplasmic and extracellular 3- and 6-linked glucans but had no effect on the synthesis of capsular acidic extracellular polysaccharides.