Why do Prokaryotes Regulate Membrane Fluidity?

While adaptation of microbial membrane lipid composition is widely observed in response to changes in temperature, and in some cases to the presence of membrane-fluidizing substances, the physiological importance of such adaptations remains largely unexplored. To shed some light on this question question we have used our ability to extensively vary the membrane fatty acid composition of Acholeplasma laidalawii B to study a variety of membrane functions is membranes whose lipids contain a single fatty acyl species whose structure and physical properties can be widely varried. Our results suggest that control of the membrane lipid phase state is considerably more important to the proper functioning of the organism than is control of the ‘fluidity’ of liquid-crystalline lipids.