Sunday, May 4, 2008
4-43

Effects of NADH-dependent xylose reductase on cofermentation of glucose and xylose to ethanol by recombinant Saccharomyces cerevisiae.

Sung H. Lee1, Hyun Jung Jung1, Yong C. Park1, Seiya Watanabe2, Tsutomu Kodaki2, K. Makino2, and Jin-Ho Seo1. (1) Agricultural Biotechnology, Seoul National University, 599 Gwanangno, Gwanak-gu, Seoul, South Korea, (2) Kyoto University, Advanced Energy, Kyoto 615-8530, Kyoto, Japan

Saccharomyces cerevisiae needs both xylose reductase (XR) and xylitol dehydrogenase (XDH) for conversion of xylose to ethanol. Cofactor imbalance of the two enzymes often results in accumulation of xylitol, which is one of the main reasons for low ethanol yield. NADPH-dependent XR was engineered to change its cofactor specificity to NADH [J. Biol. Chem. (2005) 280, 10340]. The mutated XR (NADH-dependent) and wild XDH (NADH-dependent) were introduced into a host cell S. cerevisiae D452-2 to line up with cofactor specificity. The constructed S. cerevisiae was tested for ethanol production from a mixture of glucose and xylose. The recombinant yeast grown in aerobic condition was able to utilize xylose at 1.04 g/l¤ýhr consumption rate without producing xylitol and ethanol. A change of growth condition to O2-limited allowed production of ethanol with final ethanol concentration 38 g/l and 25% (g ethanol per g xylose used) ethanol yield.

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