Structure of the extracellular bacterial polysaccharide from Arthrobacter viscosus NRRL B-1973

Abstract

D-Glucose, D-galactose, and D-mannuronic acid in equimolar proportions constitute 75% of the weight of the polysaccharide elaborated by Arthrobacter viscosus NRRL B-1973. O-Acetyl groups account for the remaining 25% of the weight; 50% of the hydroxyl groups are acetylated. Acid hydrolysis of the polysaccharide revealed that the D-mannopyranosyluronic acid bonds hydrolyzed with unexpected ease. Controlled acid hydrolysis afforded three oligosaccharides identified as 4-O-β-D-glucopyranosyl-D-galactose; 4-O-β-D-mannopyranosyluronic acid-D-glucose; and O-β-D-mannopyranosyluronic acid-(1 → 4)-O-β-D-glucopyranosyl-(1 → 4)-D-galactose. The native polysaccharide was oxidized slowly by sodium metaperiodate and consumed 0.42 mole per sugar residue in 340 h at 4°. The deacetylated polysaccharide consumed 0.67 mole of periodate per sugar residue and produced 1 mole of acid per 160 to 165 sugar residues in 170 h at 4°. At 20° the deacetylated polysaccharide was oxidized excessively by periodate, 1.5 moles of oxidant was consumed, and 0.4 mole of acid was produced per sugar residue in 340 h. However, only 20% of the C₄-substituted D-glucose residues in the polysaccharide was cleaved by periodate in spite of the excessive oxidation at 20°.The polysaccharide has a linear structure and consists predominantly of repeating trisaccharide units, O-β-D-mannopyranosyluronic acid-(1 → 4)-O-β-D-glucopyranosyl-(1 → 4)-D-galactose.