PHOSPHATE GROUPS IN LIPOPOLYSACCHARIDES OF SALMONELLA-TYPHIMURIUM RFAP MUTANTS

Lipopolysaccharides (LPS) of Salmonella typhimurium rfaP mutants and o f a galE strain as a control were subjected to analysis by P-31-NMR in order to assess the location of phosphate groups. This was done to ob tain direct proof for our earlier finding by chemical analysis that ph osphate was lacking in the core oligosaccharide part of the mutant LPS , whereas the core oligosaccharide normally contains several phosphate groups, Such phosphate deficiency has been associated with the increa sed susceptibility of the rfaP mutants to hydrophobic antibiotics and detergents, Analysis of the de-O-acylated LPS derivatives of S. typhim urium rfaP strains SH7770, SH8551, and SH8572 by P-31-MMR revealed an almost total lack of phosphate groups in the core oligosaccharide part , the LPS phosphates being largely accounted for by the two monophosph ate monoesters of lipid A, linked to positions C-1 and C-4' of the lip id A backbone. Core oligosaccharide-linked phosphates were detected in minor proportions only, indicating the presence of some normally phos phorylated core oligosaccharide, due to the inherently leaky nature of the mutation. (C) 1997 Federation of European Biochemical Societies.