Thursday, May 5, 2011: 1:30 PM
Grand Ballroom B, 2nd fl (Sheraton Seattle)
Although cellulosic ethanol holds promise in helping to relieve U.S. dependence on imported oil, a number of molecular barriers currently exist that prevent efficient and productive bioconversion of plant feedstocks into ethanol. While commonly employed in the production of corn ethanol, the brewer’s yeast Saccharomyces cerevisiae is not natively equipped to ferment xylose, the predominant pentose sugar in hemicellulose. Additionally, side products generated from the pretreatment of plant biomass are known to illicit a cellular stress response, which in turn impairs fermentation. At the Great Lakes Bioenergy Research Center (GLBRC), we have taken a multi-faceted approach aimed at identifying, addressing and overcoming these barriers that hinder fermentation of plant feedstocks into ethanol by yeast. Through multi-phenotypic screening of over 100 natural isolates, we have identified a wild S. cerevisiae strain with tolerance to high levels of ethanol and elevated temperature, and is one of the fastest growing strains in multiple cellulosic hydrolysates. To address the ineffectiveness in xylose fermentation, we employed genetic engineering, directed evolution and comparative functional genomics of xylose-fermenting yeast species, resulting in improved metabolism of xylose by our strain. In fermentation experiments with AFEX-pretreated corn stover hydrolysate, the engineered GLBRC strains produced almost as much ethanol as an industrial benchmark strain. Interestingly, while the viability of benchmark strain was dramatically reduced over time when cultured in unfiltered AFEX hydrolysate, the GLBRC strain maintained significantly higher viability. Currently, this engineered strain is undergoing transcriptomic and metabolomic profiling, which may reveal additional bottlenecks that will be targeted for improvement.