The cis/trans isomerization of the double bond of a fatty acid as a strategy for adaptation to changes in ambient temperature in the psychrophilic bacterium, Vibrio sp. strain ABE-1

Abstract

The major phospholipid, phosphatidylethanolamine (PE), of Vibrio sp. strain ABE-1 contains a unique trans-unsaturated fatty acid, 9- trans-hexadecenoic acid (16:1(9t)), at the the sn-2 position of the glycol moiety. The major molecular species of PE that contain 16:1(9t) at the sn-2 position have either 9- cis-hexadecenoic acid (16:1(9c)) or hexadecanoic acid (16:0) at the sn-1 position. The transition temperatures of the liquid-crystal to the gel phase of 16:1(9c)/16:1(9t)-PE and 16:0/16:11(9t)-PE were −3°C and 38°C, respectively, temperatures that were 31°C and 18°C higher than the corresponding temperatures for 16:1(9c)/16:1(9c)-PE and 16:0/16:1(9c)-PE. The proportion of 16:1(9c)/16:1(9t)-PE and 16:0/16:1(9t)-PE increased significantly in cells grown at 20°C over that in cells grown at 5°C. When cells grown at 5°C were incubated at 20°C in the presence of cerulenin, an inhibitor of the synthesis de novo of fatty acids, the level of 16:1(9t) increased almost in parallel with a concomitant decrease in the level of 16:1(9c) at the sn-2 position. These results suggest that 16:1(9c) is converted to 16:1(9t) by the cis/trans isomerization of the double bond in the fatty acid. This conversion is discussed as a possible strategy for adaptation by bacteria to changes in temperature.