Changes in membrane fatty acid composition of Pseudomonas aeruginosa in response to UV-C radiations.

The changes in lipid composition enable the micro-organisms to maintain membrane functions in the face of environmental fluctuations. The relationship between membrane fatty acid composition and UV-C stress was determined for mid-exponential phase and stationary phase Pseudomonas aeruginosa. The total lipids were obtained by dichloromethane/methanol (3:1) and were quantified by GC. The TLC analysis of phospholipids showed the presence of three major fractions phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. Significant modifications, as manifested by an increase of UFA, were obtained. Interestingly, this microorganism showed a remarkable capacity for recovery from the stressful effects of UV-C.

Effects of dam and/or seqA mutations on the fatty acid and phospholipid membrane composition of Salmonella enterica serovar Typhimurium.

We examined the phospholipids (Phls) and the membrane fatty acid (FA) composition in Salmonella enterica serovar Typhimurium dam and/or seqA mutants. Phosphatidylglycerol, phosphatidylethanolamine (PE), and cardiolipin (CL) are the major Phls present in all the strains and accounted for greater than 95% of the total lipid phosphorus. Phosphatidic acid and phosphatidylserine are the minor ones. The seqA mutant showed a decrease in PE and an increase in CL and phosphatidylglycerol proportion compared with the wild-type strain. The same changes were observed with the seqA dam double mutant. However, the dam mutation caused an unusual accumulation of CL with a significant decrease in the PE content, compared with the isogenic wild-type strain. FA composition of the total lipids and the different fractions containing Phls have been determined. The major saturated FAs (SFAs) and unsaturated FAs (UFAs) found were C(14:0), C(16:0) and C(16:1w7), C(18:1w9), respectively. Cyclic FAs, cyc(17:0) and cyc(19:0), were also present in appreciable amounts. Moreover, dam and/or seqA mutations caused a decrease in UFA/SFA ratio and there was a progressive reduction in the content of C(16:1w7) and C(18:1w9), going through the order seqA, dam/seqA, and dam mutants. This decrease in UFA content was compensated for in all strains by an increase in the corresponding C(17-) and C(19-) cyclic FAs. So these UFAs were converted to their cyclopropane derivatives, which resulted in a low UFA/SFA ratio. SeqA and Dam proteins might regulate FA biosynthesis and Phls composition of Salmonella enterica serovar Typhimurium.