EFFECT OF SALT STRESS ON LIPID-COMPOSITION AND MEMBRANE FLUIDITY OF THE SALT-TOLERANT YEAST ZYGOSACCHAROMYCES-ROUXII

When the salt-tolerant yeast Zygosaccharomyces rouxii was grown in YPD medium containing 15% (w/v) NaCl, the relative amounts of C-16:1 and C-18:1 fatty acids in acyl lipids increased and those of C-18:0 and C-18:2 acids decreased both in whole cells and in crude plasma membrane preparations, as compared with cells grown in YPD medium alone. The proportions of C-12:0 and C-14:0 acids, which are minor components of yeast lipids, decreased in whole cells and markedly increased in plasma membranes when 15% NaCl was included in the growth medium. The degree of unsaturation of fatty acids in the membranes and in whole cells decreased in the presence of 15% NaCl in the culture medium. The amount of free ergosterol in the membranes of cells grown in 15% NaCl increased to 2.9 times that of control cells. The ratio of ergosterol to phospholipid increased to 5 times that of control cells, whereas the ratio of phospholipid to protein in the membranes of cells grown in 15% NaCl decreased to less than half that of control cells. The fluorescence polarization value of DPH (1,6-diphenyl-1,3,5-hexatriene) in membranes of cells grown in 15% NaCl was 1.2 times higher than that for membranes from control cells, indicating a decrease in membrane fluidity in the presence of a high concentration of NaCl.