Effects of Ox Bile Extract on the Phospholipids and Fatty Acids Membrane Composition of Salmonella enterica Serovar Typhimurium seqA Mutant Strain

We examined the effect of bile on the phospholipids (PL) and the membrane fatty acid (FA) composition in Salmonella enterica serovar Typhimurium (S.Typhimurium) wild type (WT) and seqA mutant strains. Phosphatidylglycerol (PtdGro), phosphatidylethanolamine (PtdEtn) and Cardiolipin (Ptd2Gro) are the major PL present in all the strains. The ox bile stress highly affected the PL contents of the seqA mutant with an unusual decrease in PtdEtn and a great increase in Ptd2Gro and PtdGro proportion compared with the untreated seqA and the isogenic WT strains. FA composition of the total lipid (TL) and the different fractions containing PL were altered. Moreover, seqA and ox bile stress caused an increase in unsaturated FA/saturated FA ratio (UFA/SFA) and there was an increase in the content of C16:1w7 and C18:1w9. This increase in UFA content was compensated by a decrease in the corresponding C17- and C19- cyclic FA (CFA). So these CFA were converted to UFA, which resulted in a high UFA/SFA ratio. This paper provides further evidence consistent with the view that the SeqA protein might regulate biosynthesis of membrane FA and PL of S. Typhimurium and it is required for membrane protection from bile salts during infection process.