Relationship between ethanol tolerance, lipid composition and plasma membrane fluidity in Saccharomyces cerevisiae and Kloeckera apiculata.

The lipid composition of a strain of each of two yeasts, Saccharomyces cerevisiae and Kloeckera apiculata, with different ethanol tolerances, was determined for cells grown with or without added ethanol. An increase in the proportion of ergosterol, unsaturated fatty acid levels and the maintenance of phospholipid biosynthesis seemed to be responsible for ethanol tolerance. The association of ethanol tolerance of yeast cells with plasma membrane fluidity, measured by fluorescence anisotropy, is discussed. We propose that an increase in plasma membrane fluidity may be correlated with a decrease in the sterol:phospholipid and sterol:protein ratios and an increase in unsaturation index.