Abstract
Adaptation to altered osmotic conditions is a fundamental property of living cells and has been studied in detail in the yeast Saccharomyces cerevisiae. Yeast cells accumulate glycerol as compatible solute, controlled at different levels by the High Osmolarity Glycerol (HOG) response pathway. Up to now, essentially all osmostress studies in yeast have been performed with glucose as carbon and energy source, which is metabolised by glycolysis with glycerol as a by-product. Here we investigated the response of yeast to osmotic stress when yeast is respiring ethanol as carbon and energy source. Remarkably, yeast cells do not accumulate glycerol under these conditions and it appears that trehalose may partly take over the role as compatible solute. The HOG pathway is activated in very much the same way as during growth on glucose and is also required for osmotic adaptation. Slower volume recovery was observed in ethanol-grown cells as compared to glucose-grown cells. Dependence on key regulators as well as the global gene expression profile were similar in many ways to those previously observed in glucose-grown cells. However, there are indications that cells re-arrange redox-metabolism when respiration is hampered under osmostress, a feature that could not be observed in glucose-grown cells.
Highlights
Cells frequently experience changes in the water activity of their surrounding and have developed mechanisms to adapt to such changes
The response of S. cerevisiae to hyperosmotic shock on glucose is very well studied and the High Osmolarity Glycerol (HOG) pathway is a paradigm for stress-induced MAPK pathways[6]
Global gene expression profiles have been studied repeatedly and a large number of physiological data have been collected, last but not least concerning the control of glycerol accumulation by Hog[1]
Summary
Cells frequently experience changes in the water activity of their surrounding and have developed mechanisms to adapt to such changes. The response of yeast to hyperosmotic stress has exclusively been studied on cells grown with glucose as a carbon source, i.e. under conditions where respiration is inhibited and fermentative metabolism is dominating. Not glycerol, under osmotic stress with ethanol as carbon source.
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