Improving the ethanol yield by reducing glycerol formation using cofactor regulation in Saccharomyces cerevisiae.

To increase ethanol yield and decrease glycerol production in Saccharomyces cerevisiae, the strategies of direct cofactor-regulation were explored. During anaerobic batch fermentations, the yeast expressing Bacillus cereus gapN gene, encoding non-phosphorylating NADP-dependent glyceraldehyde-3-phosphate dehydrognease, produced 73.8 g ethanol l, corresponding to 96% of theoretical maximum yield compared to 92% for the wild type. The yeast expressing Escherichia coli frdA gene encoding the NAD-dependent fumarate reductase, exhibited a 22% (relative to the amount of substrate consumed) increase in glycerol yield in medium containing 2 g fumarate l. The yeast expressing mhpF gene, encoding acetylating NAD-dependent acetaldehyde dehydrogenase, produced 74.5 g ethanol l, corresponding to 97.4% of theoretical maximum yield while glycerol decreased by 40% when acetic acid was added before inoculation. This strain represents a promising alternative for ethanol production with lignocellulosic hydrolysates where acetate is available at significant amounts. [ABSTRACT FROM AUTHOR]