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Poster Presentation 2-08
Analysis of the Expression of the Genes Encoding Some of the Major Enzymes Involved in Cofermenting Glucose and Xylose to Ethanol
Miroslav Sedlak and Nancy W. Y. Ho
Laboratory of Renewable Resources Engineering (LORRE), 1295 Potter Center, Purdue University, West Lafayette, Indiana 47907
Telephone: (765) 494-7046; Fax: (765) 494-7046; E-mail: sedlak@purdue.edu
The naturally occurring Saccharomyces yeasts, particularly those superior for fermenting glucose to ethanol, are unable to metabolize xylose aerobically or anaerobically. We succeeded in developing metabolically engineered yeasts that not only metabolized xylose effectively, but could also effectively coferment both glucose and xylose simultaneously to ethanol by altering some of the control mechanisms present in microbial cells. However, our genetically engineered yeasts can still be further improved. For example, our engineered yeasts still utilize glucose much faster than xylose, particularly when the glucose concentration is high. The rate of xylose fermentation is further lowered after 5-6 hrs in glucose-depleted media or when xylose concentration is very low. One reason might be that the glucose transporters in yeast also transport xylose but greatly favor transporting glucose over xylose. It has been reported that at least 7 major glucose transporters (HXT1-7) are expressed under different growth conditions. Another reason might be that some of genes encoding major glycolytic enzymes do not express well in the absence of glucose. Using DNA microarray techniques, we are analyzing the expression of genes encoding the transport proteins and other key enzymes involved in ethanol fermentation in the presence and absence of glucose during co-fermentation of glucose and xylose to ethanol. We will report the results from such analyses.
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