Sunday, April 29, 2007

Ethanol, stress and working with yeast

Grant A. Stanley1, Meredith Chandler1, Dragana Stanley1, Idris Mohammed1, Sarah Fraser1, Peter Rogers2, and Paul J. Chambers3. (1) Molecular Sciences, Victoria University, Hoppers Lane, Werribee, 3030, Australia, (2) Carlton and United Breweries Ltd, Southampton Crescent, Melbourne, 3067, Australia, (3) The Australian Wine Research Institution, Adelaide, 5064, Australia

Ethanologenic fermentation is traditionally associated with beverage production however it has an increasingly important role in the biofuel industry. A major factor affecting fermentation productivity is microbial sensitivity to ethanol toxicity, which slows fermentation rates, reduces ethanol yields and limits microbial lifespan. Victoria University is investigating ways of reducing the impact of ethanol toxicity on microbial performance by improving the inherent ethanol-stress protective responses in yeast, which are compromised at high ethanol concentrations.  Our research focuses on identifying and characterising the key genes associated with the cell’s defence against ethanol toxicity by following transcriptome changes in yeast during ethanol stress. By comparing gene expression profiles of ethanol stressed and unstressed cells, we identified a large number of genes with altered expression levels in response to ethanol stress. These genes were grouped according to their cellular function, but it was likely that not all of them have an important role in ethanol tolerance.  To single out genes that have a key role in the ethanol stress response, we examined transcription in ethanol-stressed yeast in the presence of small quantities of acetaldehyde (which stimulates ethanol stress adaptation rates) and also in mutants that were raised with increased ethanol tolerance. Comparing the results from all three experimental approaches identified a number of areas of cell function that are particularly sensitive to ethanol stress.  One of these being central glycolytic catabolism, with glyceraldehyde 3-phosphate dehydrogenase being particularly affected, possibly due to a redox imbalance during the early stages of acclimatisation to ethanol stress.