Osmotic Stabilization of Unsaturated Fatty Acid Auxotrophs of Escherichia coli

Under osmotically stabilized conditions E. coli can grow with an unsaturated fatty acid content of 8 to 11 % in the membrane. These membranes are fragile due to the abnormally low content of unsaturated fatty acids. Thus, the unsaturated fatty acids in the membrane do function to stabilize the membranes against osmotic pressure and to increase the efficiency of biochemical reactions in the membrane. Unsaturated fatty acid-requiring auxotrophs of E. coli (1—5) are useful for elucidation of the significance of the fatty acyl group of lipids in biological membranes. By using these auxo-trophs, it was demonstrated that E. coli has selective mechanisms for fatty acids in mem-brane lipids (3, 6—9) in order to maintain the membrane lipids in an expanded liquid crys-talline state in which the membranes func-tion normally (8). Unsaturated fatty acid