Novel genetic engineered yeast strains (Saccharomyces cerevisae) have been established that produce increased ethanol yield while simultaneously reduce the production of the unwanted by-product glycerol. It is a strong industrial interest to reduce the glycerol formation during glucose catabolism and thereby increasing ethanol yield, also because glycerol disturbs the distillation process. Past approaches to reduce glycerol formation based e.g. on the deletion of either one or the two genes gpd1 and gpd2 of glycerol-3-phosphate dehydrogenase (GPDH), which is the rate-controlling enzyme in the glycerol formation pathway of the yeast Saccharomyces cerevisae. These isoenzymes play also a crucial role in osmoregulation and redox balance. While single deletion of either gpd1 or gpd2 does not noticeble decrease glycerol production, the gpd1∆gpd2∆ double deletion strain produces no glycerol, however with the negative side effect that growth and ethanol production is abolished under anaerobic conditions and strongly reduced under aerobic conditions.<br><br> In the novel genetic engineering approaches, a) the Gpd1 enzyme activity is only partly reduced in a gpd2∆-deleted CEN-PK113 yeast strain background by replacing the strong natural gpd1 promotor by a weak TEF1 promotor mutant or b) both enzyme activities of GPD1 and GPD2 are partly reduced. The strains with reduced GPD1 and GPD2 activity show an increase in ethanol production by 2-5% and a reduction in glycerol formation by 61-88% compared to wild type and a slight better growth rate than the TEFmut:GPD1 gpd2∆-strain (ethanol increase: 6,3%; glycerol formation reduction by 64%).
The technology was developed at the Technische Universität Berlin.
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