Construction of efficient xylose-fermenting Saccharomyces cerevisiae through a synthetic isozyme system of xylose reductase from Scheffersomyces stipitis

Engineered Saccharomyces cerevisiae has been used for ethanol production from xylose, the abundant sugar in lignocellulosic hydrolyzates. Development of engineered S. cerevisiae able to utilize xylose effectively is crucial for economical and sustainable production of fuels. To this end, the xylose-metabolic genes (XYL1, XYL2 and XYL3) from Scheffersomyces stipitis have been introduced into S. cerevisiae. The resulting engineered S. cerevisiae strains, however, often exhibit undesirable phenotypes such as slow xylose assimilation and xylitol accumulation. This work was undertaken to construct an improved xylose-fermenting strain by developing a synthetic isozyme system of xylose reductase (XR). The DXS strain having both wild XR and mutant XR showed low xylitol accumulation and fast xylose consumption compared to the engineered strains expressing only one type of XRs, resulting in improved ethanol yield and productivity. These results suggest that the introduction of the XR-based synthetic isozyme system is a promising strategy to develop efficient xylose-fermenting strains.