Abstract
The presence of fermentation inhibitors in lignocellulose hydrolysates is an obstacle for achieving efficient fermentation of lignocellulose hydrolysates to ethanol and other commodities. In this investigation, the possibility of generating more inhibitor-resistant Saccharomyces cerevisiae by genetic engineering was explored. Based on previous results from studies of deletion mutants, three S. cerevisiae genes ( ATR1, FLR1, YAP1) involved in multidrug resistance and stress response of yeast were selected for overexpression in three S. cerevisiae strains. The resistance of the transformed strains to lignocellulose-derived fermentation inhibitors and a dilute-acid spruce hydrolysate was evaluated in fermentation experiments. Overexpression of FLR1 resulted in enhanced resistance to the phenolic inhibitor coniferyl aldehyde and the furan aldehyde HMF (5-hydroxymethyl-2-furaldehyde). Overexpression of ATR1 conferred increased resistance to coniferyl aldehyde. Strains overexpressing YAP1, which encodes a transcription factor, displayed increased resistance to coniferyl aldehyde, HMF, and the spruce hydrolysate. An ethanol productivity of 0.17 g ethanol × l −1 × h −1 was achieved for a YAP1-overexpressing transformant cultivated in spruce hydrolysate, whereas a control transformant, which did not overexpress YAP1, only reached a productivity of 0.05 g ethanol × l −1 × h −1.
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