Alteration of xylose reductase coenzyme preference to improve ethanol production by Saccharomyces cerevisiae from high xylose concentrations

A K270R mutation of xylose reductase (XR) was constructed by site-direct mutagenesis. Fermentation results of the F106X and F106KR strains, which carried wild type XR and K270R respectively, were compared using different substrate concentrations (from 55 to 220 g/L). After 72 h, F106X produced less ethanol than xylitol, while F106KR produced ethanol at a constant yield of 0.36 g/g for all xylose concentrations. The xylose consumption rate and ethanol productivity increased with increasing xylose concentrations in F106KR strain. In particular, F106KR produced 77.6g/L ethanol from 220 g/L xylose and converted 100 g/L glucose and 100g/L xylose into 89.0 g/L ethanol in 72h, but the corresponding values of F106X strain are 7.5 and 65.8 g/L. The ethanol yield of F106KR from glucose and xylose was 0.42 g/g, which was 82.3% of the theoretical yield. These results suggest that the F106KR strain is an excellent producer of ethanol from xylose.