Elimination of glycerol and replacement with alternative products in ethanol fermentation by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> |
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Authors: | Vishist K Jain Benoit Divol Bernard A Prior Florian F Bauer |
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Institution: | (1) Institute for Wine Biotechnology, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa; |
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Abstract: | Glycerol is a major by-product of ethanol fermentation by Saccharomyces cerevisiae and typically 2–3% of the sugar fermented is converted to glycerol. Replacing the NAD+-regenerating glycerol pathway in S. cerevisiae with alternative NADH reoxidation pathways may be useful to produce metabolites of biotechnological relevance. Under fermentative
conditions yeast reoxidizes excess NADH through glycerol production which involves NADH-dependent glycerol-3-phosphate dehydrogenases
(Gpd1p and Gpd2p). Deletion of these two genes limits fermentative activity under anaerobic conditions due to accumulation
of NADH. We investigated the possibility of converting this excess NADH to NAD+ by transforming a double mutant (gpd1∆gpd2∆) with alternative oxidoreductase genes that might restore the redox balance and produce either sorbitol or propane-1,2-diol.
All of the modifications improved fermentative ability and/or growth of the double mutant strain in a self-generated anaerobic
high sugar medium. However, these strain properties were not restored to the level of the parental wild-type strain. The results
indicate an apparent partial NAD+ regeneration ability and formation of significant amounts of the commodity chemicals like sorbitol or propane-1,2-diol. The
ethanol yields were maintained between 46 and 48% of the sugar mixture. Other factors apart from the maintenance of the redox
balance appeared to influence the growth and production of the alternative products by the genetically manipulated strains. |
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