Lipopolysaccharide Heterogeneity in <i>Salmonella typhimurium</i> Analyzed by Sodium Dodecyl Sulfate/Polyacrylamide Gel Electrophoresis

Abstract

Salmonella typhimurium strains deficient in uridine diphosphate glucose epimerase were specifically labelled in the lipopolysaccharide by growing them with [ 14 C]galactose. Electrophoretic analysis of isolated cell envelopes in the presence of sodium dodecyl sulfate revealed at least 40 regularly spaced bands. This banding pattern was stable in boiling dodecyl sulfate, and did not correspond to the pattern of polypeptides. A similar pattern was obtained from the isolated lipopolysaccharide. Mutant bacteria whose lipopolysaccharide contains only the core portion of the molecule gave only the fastest moving band. Bacteria whose lipopolysaccharide has only one repeating unit gave only two bands, one apparently corresponding to the core, the other moving somewhat slower. Bacteria with wild‐type lipopolysaccharide gave bands corresponding to both of these, plus a large number of progressively more slowly moving ones, most likely representing lipopolysaccharide molecules with increasing numbers of repeating units in the O side chain. The distribution of chain lengths was unequal so that 77% of molecules with side chains had from 19 to 34 repeating units. On the other hand, two thirds of all lipopolysaccharide molecules were devoid of O side chains. In addition to this major heterogeneity due to differences in chain lengths, a second heterogeneity was indicated by the double character of each band.