ARS | Publication request: Evaluation of engineered xylose-fermenting industrial strains of Saccharomyces cerevisiae for improved ethanol production from lignocellulosic feedstocks

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: May 6, 2009
Publication Date: N/A

Technical Abstract: Saccharomyces cerevisiae is currently used to produce ethanol from glucose, but it cannot utilize five-carbon sugars contained in the hemicellulose component of biomass feedstocks. Hemicellulose can make up to 20-30% of biomass and is primarily composed of xylose. Enzymes from native xylose-assimilating organisms have been transferred to S. cerevisiae, allowing fermentation of xylose. However, efficient conversion of xylose to ethanol is limited, putatively by cellular redox imbalance, low flux of xylose into the pentose phosphate pathway, and lack of efficient xylose transport into the cell. Genetic background has been demonstrated to play a vital role in the fermentation capacity and stress tolerance of laboratory and industrial yeast strains. The goal of this study was to compare xylose fermentation properties of several industrial yeast strains in order to identify a genetic background conferring improved xylose fermentation. Six industrial strains of S. cerevisiae from the Agricultural Research Service (ARS) culture collection were engineered to express the Pichia stipitis genes encoding xylose reductase and xylitol dehydrogenase, as well as the S. cerevisiae xylulokinase gene. Each gene was expressed from a different constitutive, high-level promoter. The three genes were stably integrated at the HO endonuclease site on chromosome IV. The resulting strains were analyzed to determine xylose consumption rates and ethanol productivities. One of the strains showed superior xylose growth and consumption compared to our haploid lab strain and other engineered industrial strains. Xylose fermentation data for the different strains will be presented.