Monday, April 19, 2010
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Effects of modulation of glycerol metabolism on bioethanol production in recombinant Saccharomyces cerevisiae DGPD1DGDH1

Jin-Woo Kim1, Jeong-Eun Lee1, Yong-Cheol Park2, and Jin-Ho Seo3. (1) Department of Agricultural Btiotechnology, Seoul National University, Room 200A-Bio8104, San 56-1, Shillim-dong, Kwanak-gu, Seoul, South Korea, (2) Department of Advanced Fermentation Fusion Science and Technology, Kookmin University, 861-1 Jeongneung-Dong Seongbux-Gu, Seoul, South Korea, (3) Department of Agricultural Biotechnology, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, Seoul, South Korea

Current bioethanol technology has been developed by using corn and sugarcane as two major feed stocks. By simple physical and biological processes, corn starch is degraded to generate glucose. A work-horse for bioethanol production, Saccharomyces cerevisiae converted glucose into ethanol with by-products such as glycerol, acetate, pyruvate and succinate. Among them, about 2 ~ 5% of total carbon sources are used for accumulation of glycerol because of the imbalance of NADH/NAD+ level in anaerobic conditions. To investigate the effects of cofactor level perturbation on glycerol formation and ethanol production, the GPD1 gene coding for glycerol-3-phosphate dehydrogenase and GDH1 gene coding for glutamate dehydrogenase were deleted in the chromosome of S. cerevisiae in this study. Double deletion of the two genes in S. cerevisiae DGPD1DGDH1 led to a decrease in glutamate dehydrogenase activity consuming NADPH and concomitant increased both glutamate synthetase and glutamate synthase activities using NADH as a cofactor. Anaerobic batch fermentation of the recombinant S. cerevisiae DGPD1DGDH1 resulted in 48% and 55% decreases in glycerol and acetate concentrations compared with the wild type strain, respectively. Cofactor-engineering by double deletion of the GPD1 and GDH1 genes redirected the carbon flux for glycerol and acetate production into ethanol production, and resulted in improvement of ethanol yield by 3.2% relative to the wild type strain.

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