Impact of Exogenous Fatty Acid on Ethanol-induced Alterations in Phospholipid Fatty Acid Composition of Plasma Membranes of a Self-flocculating Yeast

Ethanol-induced alterations in phospholipid fatty acid composition of plasma membranes of a self-flocculating fusant of Schizosaccharomyces pombe and Saccharomyces cerevisiae grown in the presence of exogenously supplemented fatty acid were investigated. The addition of palmitic acid (0.6 mmol/L) to the medium containing 6%～9% (V/V) ethanol resulted in a marked increase in the palmitic acid content and decreases in the contents of myristoleic, palmitoleic, and oleic acids in the phospholipid fatty acid composition of plasma membranes, as compared with their contents in the absence of ethanol. On the other hand, the addition of both linoleic acid (0.6 mmol/L) and ethanol (6%～9%, V/V) to the basal medium resulted in a striking increase in oleic acid and corresponding decreases in myristoleic, palmitoleic and palmitic acids, while the linoleic acid content was slightly increased. Moreover, the addition of both linolenic acid (0.6 mmol/L) and ethanol (6%～9%, V/V) also resulted in a significant increase in oleic acid and corresponding decreases in myristoleic, palmitoleic and palmitic acids, however, the linolenic acid levels were decreased. All these alterations (especially increases in palmitic acid and oleic acid) were confirmed to be the adaptive responses of cells to ethanol because cells grown with both fatty acid and ethanol acquired a pronounced increase in viability and a corresponding decrease in plasma membrane permeability when they were subsequently exposed to high concentration of ethanol. These data suggest that both palmitic acid and oleic acid are able to enhance the tolerance of the self-flocculating yeast to ethanol by strengthening plasma membrane permeability barrier of this strain subjected to ethanol stress. This is a novel phenomenon because enhancement by unsaturated and saturated fatty acids on ethanol tolerance occurs in the same strain.