Over-expressing GLT1 in a gpd2Delta mutant of Saccharomyces cerevisiae to improve ethanol production.

We constructed two recombinant strains of Saccharomyces cerevisiae in which the GPD2 gene was deleted using a one-step gene replacement method to minimize formation of glycerol and improve ethanol production. In addition, we also over-expressed the GLT1 gene by a two-step gene replacement method to overcome the redox-imbalancing problem in the genetically modified strains. The result of anaerobic batch fermentations showed that the rate of growth and glucose consumption of the KAM-5 (MATalpha ura3 gpd2Delta::RPT) strain were slower than the original strain, and the KAM-13 (MATalpha ura3 gpd2Delta::RPT P ( PGK ) -GLT1) strain, however, was indistinguishable compared to the original strain using the same criteria, as analyzed. On the other hand, when compared to the original strain, there were 32 and 38% reduction in glycerol formation for KAM-5 and KAM-13, respectively. Ethanol production increased by 8.6% for KAM-5 and 13.4% for KAM-13. Dramatic reduction in acetate and pyruvic acid was also observed in both mutants compared to the original strains. Although gene GPD2 is responsible for the glycerol synthesis, the mutant KAM-13, in which glycerol formation was substantially reduced, was able to cope and maintain osmoregulation and redox balance and have increased ethanol production under anaerobic fermentations. The result verified the proposed concept of increasing ethanol production in S. cerevisiae by genetic engineering of glycerol synthesis and over-expressing the GLT1 gene along with reconstituted nicotinamide adenine dinucleotide metabolism.