Oral Presentation 2-03

Engineering Stable Recombinant Saccharomyces Yeast

Capable of Effective Co-utilization of Glucose and Xylose for the

Production of Ethanol, Lactic Acid, or Other Industrial Chemicals

Nancy W. Y. Ho, Miroslav Sedlak, and Zhendao Chen

Laboratory of Renewable Resources Engineering (LORRE)

Purdue University, West Lafayette, Indiana 47907-1295

Telephone and Fax:  (765) 494-7046; E-mail:  nwyho@ecn.purdue.edu

Cellulosic biomass is the largest renewable resource in the world and an ideal raw material for the production of chemicals by microbial processes.  However, cellulosic biomass contains large amounts of xylose in addition to glucose.  This limits the use of the Saccharomyces yeasts in converting cellulosic sugars to ethanol or other industrial products.   In recent years, we have succeeded in engineering the Saccharomyces yeasts to effectively metabolize xylose.  This was accomplished by cloning and overexpressing three major xylose-metabolizing genes – xylose reductase, xylitol dehydrogenase, and xylulokinase genes – in yeast, and by modifying the control mechanisms present in the microbial cells.  As a result, the metabolically engineered yeast can co-utilize glucose and xylose efficiently.  Furthermore, an effective gene integration method has also been developed, which allows the successful development of stable recombinant yeasts containing multiple copies of the cloned three xylose-metabolizing genes integrated into the yeast chromosomes.  We have demonstrated that the resulting stable recombinant yeasts can effectively coferment glucose and xylose derived from cellulosic biomass simultaneously to ethanol.  Recently, we have succeeded in further engineering the Saccharomyces yeast to effectively produce lactic acid, a product not traditionally produced by yeast, from mixed sugars of glucose and xylose.  In addition, stable lactic acid producing recombinant Saccharomyces yeasts have also been developed, and the resulting yeasts aerobically produce lactic acid most efficiently.  The results presented here serve as examples demonstrating that the safe, user-friendly Saccharomyces yeasts can be engineered to efficiently use cellulosic sugars to produce various important industrial products by either aerobic or anaerobic processes.

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