Methylation analysis of acidic exopolysaccharides of Rhizobium and Agrobacterium

Abstract

Exopolysaccharides of Agrobacterium tumefaciens and Rhizobium meliloti, containing d-glucose, d-galactose, pyruvic acid, and O-acetyl groups in the approximate proportions 6:1:1:1.5, were analysed by methylation. They were found to contain the following main structural units (all β-glycosidic): chain residues of (1→3)-linked d-glucose (24%), (1→3)-linked d-galactose (15%), (1→4)-linked d-glucose (20%), and (1→6)-linked d-glucose (18%); (1→4,1→6)-linked branching residues of d-glucose (12%), and terminal d-glucose residues substituted at positions 4 and 6 by pyruvate (11%). Uronic acid-containing exopolysaccharides of Rhizobium leguminosarum, R. phaseoli, and R. trifolii contained d-glucose, d-glucuronic acid, d-galactose, pyruvic acid, and O-acetyl groups in the approximate proportions 5:2:1:2:3. Methylation gave identical patterns of methylated sugar components, from which the following structural elements were deduced: chain residues of (1→3)-linked d-glucose substituted at positions 4 and 6 by pyruvate (13%), (1→4)-linked d-glucose (32%), and (1→4)-linked d-glucuronic acid (20%); (1→4,1→6)-linked branching residues of d-galactose and/or d-glucose (13%), and terminal d-glucose and/or d-galactose residues substituted at positions 4 and 6 by pyruvate (13%).