engleski

Effect of environmental stress factors on the content and composition of the phospholipid species of brewing strain of Saccharomyces cerevisiae

In the yeast Saccharomyces cerevisiae, as in other eukaryotes, phospholipids are essential structural components of cell membranes. The phospholipid composition of yeast cells varies greatly with the growth phase and growth conditions. Adjustments in membrane phospholipids of yeasts appear to be important in the adaptation of cells to different environmental conditions. Bottom-fermenting brewer’ s yeast analysed in this work is confronted to toxic effect of ethanol and oxygen-limited conditions during serial repitching, which brings about an adaptive response of the yeast cells. The aim of this study was to determine phospholipid composition, in particular phosphatidylcholine (PC) to phosphatidylethanolamine (PE) ratio as well as their fatty acid composition in the whole cells and plasma membrane (PM) of the pure culture (the pitching yeast) and three recycled generations (1st, 2nd and 3rd). In the recycled yeast generations, cellular content of PC was significantly higher, while the content of PE was lower comparing the pitching yeast. In the PM the contents of both phospholipid species increased from the pitching yeast to the 2nd generation. The PC:PE ratio in the whole cells and PM was higher in the recycled generations. A common characteristic of the fatty acid composition of PC and PE of whole cells and the PM was a significant prevalence of C16 fatty acids. In the composition of PC and PE of the whole cells, palmitic acid was the main one in the pitching yeast, while palmitoleic acid was in all recycled generations. In both phospholipid species of the PM the content of palmitic acid decreased while the content of palmitoleic increased from the pitching yeast to the 2nd generation. In the 3rd generation their content became almost equal in PC, while in PE the content of both acids assumed the same values as in the pitching yeast. In conclusion we may say that the PC:PE ratio, as well as their fatty acid composition varied significantly with the number of recycling. The changes were the most expressed in the 1st generation as the response to stress conditions. On the other hand, the tendency observed in the 3rd generation for some results to approach the values in the pitching yeast was due to a gradual adaptation of the yeast cells to unfavourable working conditions.

brewer's yeast; Saccharomyces cerevisiae; phospholipids; fatty acid

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