It is well known that modest concentrations of ethanol and other alcohols lead to reduced fermentation and growth rates of those organisms which produce them, and that high concentrations are cytotoxic. This would tend to suggest that the action of these alcohols is primarily located at a hydrophobic site, possibly at the membrane. Fractionation of the lipids from yeasts grown on various alkanes showed that although triglycerides still constituted the major fraction, their relative proportion was less than when glucose was the growth substrate. When grown in the presence of butanol, C. acetobutylicum synthesised increased levels of saturated acyl chains at the expense of unsaturated chains. The ratio of unsaturated to saturated fatty acids has long been known to control membrane fluidity, with increases in unsaturation leading to greater membrane fluidity, such that cells subjected to temperature changes adjust the degree of saturation to maintain a constant fluidity, a mechanism knows as homeoviscous adaptation.
Sterols also play an important role in the regulation of membrane fluidity.
Finally, Heipieper et al .