title: Effect of alternative NAD+-regenerating pathways on the formation of primary and secondary aroma compounds in a Saccharomyces cerevisiae glycerol-defective mutant.
abstract: 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.
authors: Institute for Wine Biotechnology, Stellenbosch University, Private Bag X1, Matieland, Stellenbosch, South Africa.
authors: Vishist K
authors: VK
authors: Jain
authors: Benoit
authors: B
authors: Divol
authors: Bernard A
authors: BA
authors: Prior
authors: Florian F
authors: FF
authors: Bauer
mesh_terms: D050260:Carbohydrate Metabolism; D003470:Culture Media / Q000737:chemistry; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D005421:Flavoring Agents / Q000378:metabolism*; D017353:Gene Deletion; D005990:Glycerol / Q000378:metabolism*; D050536:Glycerol-3-Phosphate Dehydrogenase (NAD+) / Q000172:deficiency; D053858:Metabolic Networks and Pathways / Q000235:genetics; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D003470:Culture Media; D005421:Flavoring Agents; D029701:Saccharomyces cerevisiae Proteins; D009243:NAD; D000431:Ethanol; C568531:GPD1 protein, S cerevisiae; C568532:GPD2 protein, S cerevisiae; D050536:Glycerol-3-Phosphate Dehydrogenase (NAD+); D005990:Glycerol