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Oral Presentation 2-04
Genome-wide Expression Analysis of Xylose Metabolism in Recombinant Saccharomyces cerevisiae Expressing PsXYL1, PsXYL2, and PsXYL3
Yong-Su Jin1 and Thomas W. Jeffries1,2,3
1Department of Food Science, University of Wisconsin-Madison 1605 Linden Drive, Madison, WI 53706, USA
2Department of Bacteriology, University of Wisconsin-Madison 1550 Linden Drive, Madison, WI 53706, USA
3USDA Forest Service, Forest Products Laboratory One Gifford Pinchot Dr., Madison, WI 53705, USA
Telephone: (608) 231-9453; Fax: (608) 231-9262; E-mail: twjeffries@fs.fed.us
Previous researchers have engineered xylose metabolism in S. cerevisiae by introducing genes (PsXYL1, PsXYL2) coding for xylose reductase and xylitol dehydrogenase from Pichia stipitis along with overexpression of the endogenous xylulokinase gene (ScXKS1). Recently we cloned the xylulokinase gene (PsXYL3) from P. stipitis and developed a recombinant S. cerevisiae strain that has a complete xylose assimilation pathway from the xylose fermenting yeast, P. stipitis. The resulting recombinant S. cerevisiae strain can grow on and produce ethanol from xylose when it is supplied as a sole carbon source. We used genome-wide expression analysis to explore how gene expression is reprogrammed in response to changes in carbon sources (glucose and xylose) and aeration (aerobic and oxygen-limited). Expression levels of genes coding for enzymes in glycolysis and the pentose phosphate pathway did not change significantly. However, expression of the genes encoding the TCA cycle and respiration pathway generally increased during xylose as compared to glucose metabolism. These results indicate that xylose is not recognized as a fermentable sugar by recombinant S. cerevisiae. Therefore, xylose metabolism in recombinant S. cerevisiae is oxidative. In an attempt to force the cells to utilize xylose as a non-oxidative manner, we created a respiration deficient mutant that cannot use carbon sources oxidatively. As a result of this deficiency, the mutant strain produced more ethanol and accumulated less xylitol from xylose.
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