Transcriptional changes associated with ethanol tolerance in Saccharomyces cerevisiae
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Saccharomyces spp. are widely used for ethanol production; however, fermentation productivity is negatively affected by the impact of ethanol accumulation on yeast metabolic rate and viability. This study used microarray and statistical two-way ANOVA analysis to compare and evaluate gene expression profiles of two previously generated ethanol-tolerant mutants, CM1 and SM1, with their parent, Saccharomyces cerevisiae W303-1A, in the presence and absence of ethanol stress. Although sharing the same parentage, the mutants were created differently: SM1 by adaptive evolution involving long-term exposure to ethanol stress and CM1 using chemical mutagenesis followed by adaptive evolution-based screening. Compared to the parent, differences in the expression levels of genes associated with a number of gene ontology categories in the mutants suggest that their improved ethanol stress response is a consequence of increased mitochondrial and NADH oxidation activities, stimulating glycolysis and other energy-yielding pathways. This leads to increased activity of energy-demanding processes associated with the production of proteins and plasma membrane components, which are necessary for acclimation to ethanol stress. It is suggested that a key function of the ethanol stress response is restoration of the NAD+/NADH redox balance, which increases glyceraldehyde-3-phosphate dehydrogenase activity, and higher glycolytic flux in the ethanol-stressed cell. Both mutants achieved this by a constitutive increase in carbon flux in the glycerol pathway as a means of increasing NADH oxidation.