Role of 1-acyl-sn-glycerol-3-phosphate acyltransferase in psychrotrophy and stress tolerance of Serratia plymuthica RVH1

A mutant with a transposon insertion just upstream of the lysophosphatidic acid acyltansferase gene plsC was isolated in a screen for mutants affected in growth at low temperature of the psychrotroph Serratia plymuthica RVH1. This mutant had lost its ability to grow at 4 °C and was severely affected in growth at 10 °C, but showed only slightly reduced growth at 30 °C. Fatty acid analysis of membrane extracts showed that the ratio of C16:1/C18:1 fatty acids was six-to sevenfold reduced in the mutant, although the ratio of unsaturated to saturated fatty acids was unaffected. The homeoviscous adaptation ability of the mutant was also unaffected. Growth and fatty acid composition were mostly restored by overexpressing plsC on a plasmid. Supplementation of C16:1 (palmitoleic acid) into the growth medium partially rescued low temperature growth, indicating that a balanced ratio of the two main unsaturated fatty acids is required for psychrotrophy. The mutant was significantly more strongly inactivated by high pressure treatment at 250 MPa, but not at higher pressures. It also showed reduced growth at low pH, but not at increased NaCl concentrations. This work provides novel information on the role of membrane fatty acid composition in stress tolerance.