Isolation of low ethanol producing yeast strains using adaptive evolution

This thesis describes the application of a non-genetic engineering approach, adaptive evolution, to generate variants of Saccharomyces cerevisiae that produce reduced levels of ethanol relative to the strains they were derived from. Sub-lethal concentrations of sulfite, which sequesters acetaldehyde, thereby limiting ethanol production, was used as a selection pressure. However, removal of acetaldehyde not only limits ethanol production, it also compromises redox balance by preventing the fermentative oxidation of NADH. To compensate for this, the cell regenerates NAD by producing increased amounts of glycerol; glycerol production is an NADH-driven reductive process. It was demonstrated in this thesis that culturing yeast in presence of sulfite for a number of generation, results in the generation of genetically stable variants with increased glycerol and reduced ethanol production