Identification of gene targets eliciting improved alcohol tolerance in Saccharomyces cerevisiae through inverse metabolic engineering

The economic production of biofuels from renewable biomass using Saccharomyces cerevisiae requires tolerance to high concentrations of sugar and alcohol. Here we applied an inverse metabolic engineering approach to identify endogenous gene targets conferring improved alcohol tolerance in S. cerevisiae. After transformation with a S. cerevisiae genomic library, enrichment of the transformants exhibiting improved tolerance was performed by serial subculture in the presence of iso-butanol (1%). Through sequence analysis of the isolated plasmids from the selected transformants, four endogenous S. cerevisiae genes were identified as overexpression targets eliciting improved tolerance to both iso-butanol and ethanol. Overexpression of INO1, DOG1, HAL1 or a truncated form of MSN2 resulted in remarkably increased tolerance to high concentrations of iso-butanol and ethanol. Overexpression of INO1 elicited the highest ethanol tolerance, resulting in higher titers and volumetric productivities in the fermentation experiments performed with high glucose concentrations. In addition, the INO1-overexpressing strain showed a threefold increase in the specific growth rate as compared to that of the control strain under conditions of high levels of glucose (10%) and ethanol (5%). Although alcohol tolerance in yeast is a complex trait affected by simultaneous interactions of many genes, our results using a genomic library reveal potential target genes for better understanding and possible engineering of metabolic pathways underlying alcohol tolerance phenotypes.