Physiological changes of Saccharomyces cerevisiae KNU5377 occurred in the process of the 48-hour ethanol fermentation at 40oC

Abstract

In this study, physiological changes in a thermotolerant yeast Saccharomyces cerevisiae KNU5377 cell exposed to 48-hour alcohol fermentation at 40oC were investigated. After 12 hours of alcohol fermentation at 40oC, the C16:1 unsaturated acid of plasma membrane increased to 1.5 times more than the C16:0 saturated fatty acid, and to about 2 times more for the C18:1 unsaturated fatty acid. Fermentation at both 30oC- and 37oC- fermentation showed the same pattern as that done at 40oC. The pH of the alcohol- fermentation medium was reduced to pH 4.1 from a starting pH of 6.0 through the 12-hr fermentation and then maintained this level during the continuing fermentation. With the process of fermentation, the remaining glucose was reduced, but its amount remaining during the 40oC-fermentation was less reduced than those fermented at 30oC and 37oC. In the study investigating the changing pattern of cellular proteins in the alcohol-fermenting cells, the SDS-PAGE and 2-D data indicated the most expressed dot was phosphoglycerate kinase, which is one enzyme involved in glycolysis. Why this enzyme was most expressed in the cells exposed to unfavorable conditions such as high temperature, increasing concentration of produced alcohol and long time exposure to other stress factors remains unsolved.