STRUCTURAL CHARACTERIZATION OF A NOVEL DIGLYCOSYL DIACYLGLYCERIDE GLYCOLIPID FROM RHIZOBIUM-TRIFOLII ANU843

A novel glycolipid was isolated by chloroform-methanol extraction of Rhizobium trifolii ANU843 cells. Compositional analysis, methylation studies, H-1 NMR and spectroscopies led to the identification of a diglycosyl diacylglyceride: 1,2-di-O-acyl-3-O-[alpha-D-glucopyranosyl-(1 --> 3)-O-alpha-D-mannopyranosyl]glycerol. Iso-hexadecanoic and anteiso-heptadecanoic acids were the predominant fatty acids esterifying the glyceryl moiety, but a microheterogeneity in fatty acid composition was found, resulting in at least five distinct molecular species of the glycolipid. Although widespread in plants, animals and Gram-positive bacteria, glycosyl glycerides have been seldom reported in Gram-negative bacteria and this work is the first evidence of their occurrence in the bacterial family Rhizobiaceae.