Two-stage transcriptional reprogramming in Saccharomyces cerevisiae for optimizing ethanol production from xylose

Conversion of lignocellulosic material to ethanol is a major challenge in second generation bio-fuel production by yeast Saccharomyces cerevisiae. This report describes a novel strategy named two-stage transcriptional reprogramming (TSTR) in which key gene expression at both glucose and xylose fermentation phases is optimized in engineered S. cerevisiae. Through a combined genome-wide screening of stage-specific promoters and the balancing of the metabolic flux, ethanol yields and productivity from mixed sugars were significantly improved. In a medium containing 50 g/L glucose and 50 g/L xylose, the top-performing strain WXY12 rapidly consumed glucose within 12 h and within 84 h it consistently achieved an ethanol yield of 0.48 g/g total sugar, which was 94% of the theoretical yield. WXY12 utilizes a KGD1 inducible promoter to drive xylose metabolism, resulting in much higher ethanol yield than a reference strain using a strong constitutive PGK1 promoter. These promising results validate the TSTR strategy by synthetically regulating the xylose assimilation pathway towards efficient xylose fermentation. Crown Copyright (C) 2014 Published by Elsevier Inc. on behalf of International Metabolic Engineering Society. All rights reserved.