Structure of the extracellular polysaccharide secreted by Rhizobium leguminosarum var. phaseoli CIAT 899

The structure of the extracellular polysaccharide secreted by Rhizobium leguminosarum var. phaseoli CIAT 899 has been studied by methylation analysis, 1H-n.m.r. spectroscopy, and partial acid hydrolysis. The repeating unit is an octasaccharide made up of d -glucose, d -galactose, pyruvic acid, and acetic acid in the molar ratios 6:2:1.5:1.5. Half of the terminal Gal groups are 4,6-substituted by pyruvic acid acetal groups and the other half by O-acetyl groups at position 3. Also, one of the 3-linked glucosyl residues carries a pyruvic acid 4,6-acetal group and one of the 4-linked glucosyl residues is acetylated at position 6.