Polyunsaturated fatty acid biosynthesis in Saccharomyces cerevisiae: expression of ethanol tolerance and the FAD2 gene from Arabidopsis thaliana.

The Arabidopsis thaliana delta-12 fatty acid desaturase gene (FAD2) was overexpressed in Saccharomyces cerevisiae by using the GAL1 promoter. S. cerevisiae harboring the FAD2 gene was capable of forming hexadecadienoyl (16:2) and linoleoyl (18:2) residues in the membrane lipid when cultured in medium containing galactose. Gas-liquid chromatography analysis of total lipids indicated that the transformed S. cerevisiae accumulated these dienoic fatty acyl residues and that they accounted for approximately 50% of the total fatty acyl residues. Phospholipid analysis of this strain indicated that the oleoyl (18:1) residue binding phosphatidylcholine (PC) was mostly converted to the 18:2 residue binding PC, whereas 50% of the palmitoleoyl (16:1) residue binding PC was converted to the 16:2 residue binding PC. A marked effect on the unsaturation of 16:1 and 18:1 was observed when S. cerevisiae harboring the FAD2 gene was cultured at 8 degrees C. To assess the ethanol tolerance of S. cerevisiae producing polyunsaturated fatty acids, the cell viability of this strain in the presence of ethanol was examined. The results indicated that S. cerevisiae cells overexpressing the FAD2 gene had greater resistance to 15% (vol/vol) ethanol than did the control cells.