Thermal regulation of the membrane lipid composition of Escherichia coli. Evidence for the direct control of fatty acid synthesis.

Starvation of strains of Escherichia coli which are glycerol auxotrophs and are also defective in beta oxidation results in the accumulation of large amounts of free fatty acid (Cronan, J. E., Jr., Weisberg, L. W., and Allen, R. G. (1975) J. Biol. Chem. 250, 5835-5840). We now report that the ratio of saturated to unsaturated species appearing in the free fatty acid fraction depends on the incubation temperature at the time of synthesis of these acids. This result indicates that fatty acid synthesis is one site of the thermal control of phospholipid fatty acid composition. We also report experiments on the incorporation of exogenously supplied fatty acids into membrane phospholipids. The effect of temperature on this incorporation supports the hypothesis that a second site of thermal regulation acts at the level of phosphatidic acid synthesis.