Optimized xylose isomerase uptake and expression level in Saccharomyces cerevisiae for improving ethanol production

The ability to engineer the yeast Saccharomyces cerevisiae to efficiently convert lignocellulosic biomass to ethanol remains a considerable challenge. Here, we propose a new reprogrammable strategy to optimize the expression level of the xylose isomerase (XI) gene with the induction of mutations in S . cerevisiae  to improve efficient ethanol production and productivity. We sought to fine-tune the xylose uptake and catabolism abilities of S. cerevisiae  during fermentation by improving efficiency of the xylose transporter, which was fused with four copies of the XI gene under the control of different promoters to obtain recombinant yeast strains. In fermentation experiments, the optimized strain CW9 cultured in yeast extract-peptone (YP) medium containing approximately 65 g/L glucose and 55 g/L xylose produced consistent ethanol yields of 0.45 g/g total sugar in about 72 h, which was close to 90% of the theoretical yield. These promising results indicate that strain CW9 is the best producer of ethanol from mixed sugar when synthetically regulating the xylose assimilation pathway. Overall, this study provides an optimal method to control XI expression levels to find better conditions for enhancing biofuel production.