Structure of Cell Wall Lipopolysaccharide from Salmonella typhimurium

Cell wall lipopolysaccharide from a semirough or SR strain of Salmonella typhimurium was studied by partial acid hydrolysis and methylation. Mutants lacking phosphomannoisomerase were utilized to prepare lipopolysaccharides specifically labeled in their mannose residues, which are found only in the “O side chain” portion of the lipopolysaccharides. After partial acid hydrolysis, the major oligosaccharide product from the SR strain was mannosyl‐rhamnose, and the longest mannose‐containing oligosaccharide isolated was mannosyl‐rhamnosyl‐galactose. In contrast, the major product from the wild type strain was galactosyl‐mannosyl‐rhamnose, and larger mannose‐containing oligosaccharides were also found. After methylation the mannose residues of the SR lipopolysaccharide gave rise only to a tri‐ O ‐methyl‐mannose, whereas the mannose resudues of the wild type lipopolysaccharide were converted mostly to a di‐ O ‐methyl‐mannose, and also to a tri‐ O ‐methyl‐ and a tetra‐ O ‐methyl‐mannose. On the other hand, gas‐liquid chromatography of acetylated methyl alditols from the SR strain indicated that the structure of the R core and of the O repeat unit was not altered. We conclude that SR strains cannot polymerize the O repeat unit, but transfer the unpolymerized “O repeat units” to the normal attachment sites on the R core.