Improvement of xylose fermentation in respiratory-deficient xylose-fermenting Saccharomyces cerevisiae

Effective conversion of xylose in lignocelluloses is expected to reduce the production cost of second-generation biofuels significantly. The factors affecting xylose fermentation in Saccharomyces cerevisiae that express xylose reductase-xylitol dehydrogenase (XR-XDH) are studied. Although overproduction of non-oxidative pentose phosphate pathway significantly increased the aerobic-specific growth rate on xylose and slightly improved conversion of xylose to ethanol under oxygen-limited conditions, the elimination of respiration by deleting cytochrome C oxidase subunit IV gene impeded aerobic growth on xylose. However, the adaptive evolution of the respiratory-deficient strain with an NADP(+)-preferring XDH mutant in xylose media dramatically improved its xylose-fermenting ability. The specific growth rate, ethanol yield, and xylitol yield of the evolved strain on xylose were 0.06h(-1), 0.39gg(-1), and 0.13gg(-1) consumed xylose, respectively. Similar to anaerobic fermentation, the evolved strain exhibited accumulated ethanol rather than recycled it under aerobic conditions.