Structure of cell wall lipopolysaccharide from Salmonella typhimurium. IV. Anomeric configuration of L-rhamnose residues and its taxonomic implications.

A major portion of cell wall lipopolysaccharide from group A, group B, or group D(1)Salmonella corresponds to a linear polysaccharide chain, which consists of alpha-d-galactosyl-(1 --> 2)-alpha-d-mannosyl-(1 --> 4)-l-rhamnosyl-(1 --> 3)-repeating units, and has short branches of single 3,6-dideoxyhexose residues. The groups differ in the configuration of the 3,6-dideoxyhexose present. Furthermore, it has been claimed that the anomeric configuration of the rhamnosyl residues is beta-l in group B, in contrast to the alpha-l configuration found in groups A and D(1). In this study, oligosaccharides containing more than one repeating unit were isolated from a lipopolysaccharide of a group B Salmonella, and the anomeric configuration of the rhamnosyl residues was determined by the comparison of optical rotatory powers of these oligosaccharides with that of the repeating unit trisaccharide. The results established the configuration of rhamnose as alpha-l, in contrast to the beta-l configuration suggested in the literature. Since rhamnosyl linkages in lipopolysaccharide of a group D(1)Salmonella are hydrolyzed in acid at exactly the same rate as are those in group B Salmonella, the configuration of rhamnose residues in groups D(1) lipopolysaccharide is also likely to be alpha-l. These results indicate that lipopolysaccharides of Salmonella groups A, B, and D(1) share an identical main chain polysaccharide and differ essentially only in the configuration of 3,6-dideoxyhexose branches; they thus suggest close evolutionary relationship between these three serogroups of Salmonella.