Browsing by Author "Jain, V. K."

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Effect of alternative NAD +-regenerating pathways on the formation of primary and secondary aroma compounds in a Saccharomyces cerevisiae glycerol-defective mutant
    (2012) Jain, V. K.; Divol, Benoit; Prior, B. A.; Bauer, Florian
    Saccharomyces cerevisiae maintains a redox balance under fermentative growth conditions by re-oxidizing NADH formed during glycolysis through ethanol formation. Excess NADH stimulates the synthesis of mainly glycerol, but also of other compounds. Here, we investigated the production of primary and secondary metabolites in S. cerevisiae strains where the glycerol production pathway was inactivated through deletion of the two glycerol-3-phosphate dehydrogenases genes (GPD1/GPD2) and replaced with alternative NAD +-generating pathways. While these modifications decreased fermentative ability compared to the wild-type strain, all improved growth and/or fermentative ability of the gpd1Δgpd2Δ strain in self-generated anaerobic high sugar medium. The partial NAD + regeneration ability of the mutants resulted in significant amounts of alternative products, but at lower yields than glycerol. Compared to the wild-type strain, pyruvate production increased in most genetically manipulated strains, whereas acetate and succinate production decreased in all strains. Malate production was similar in all strains. Isobutanol production increased substantially in all genetically manipulated strains compared to the wild-type strain, whereas only mutant strains expressing the sorbitol producing SOR1 and srlD genes showed increases in isoamyl alcohol and 2-phenyl alcohol. A marked reduction in ethyl acetate concentration was observed in the genetically manipulated strains, while isobutyric acid increased. The synthesis of some primary and secondary metabolites appears more readily influenced by the NAD +/NADH availability. The data provide an initial assessment of the impact of redox balance on the production of primary and secondary metabolites which play an essential role in the flavour and aroma character of beverages. © 2011 Springer-Verlag.
  • No Thumbnail Available
    Item
    Elimination of glycerol and replacement with alternative products in ethanol fermentation by Saccharomyces cerevisiae
    (2011) Jain, V. K.; Divol, Benoit; Prior, B. A.; Bauer, Florian
    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 (gpd1δgpd2δ) 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. © 2010 Society for Industrial Microbiology.