Low-temperature effects on cyanobacterial membranes.

The effect of change in ambient temperature on fatty acid unsaturation has been studied in the cyanobacterium Anabaena variabilis. When cells isothermally grown at 22 degrees C are compared with those grown at 38 degrees C, the relative content of oleic acid decreases and that of linolenic acid increases in all of the lipid classes. After a temperature shift from 38 to 22 degrees C, palmitic acid is rapidly desaturated in monogalactocyldiacylglycerol, but in no other lipids, and oleic acid is slowly desaturated in most lipid classes. When cells of Anacystis nidulans are exposed to low temperature such as 0 degree C, they lose physiological activities and finally die. This low-temperature damage is initiated by the phase transition of lipids in the plasma membrane. The phase transition of thylakoid membrane that occurs at intermediate temperature produces loss of activity related to photosynthesis. This is, however, recovered when the cells are rewarmed to growth temperature. A model for the mechanism of the low-temperature damage in the cyanobacterial cells is proposed.