Sunday, April 29, 2007

Impact of culture nutrition on inhibitor tolerance and the conversion of high xylose concentrations to ethanol by Pichia stipitis NRRL Y-7124

Patricia J. Slininger1, Z. Lewis Liu1, and Steven W. Gorsich2. (1) Crop BioProtection Research, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University, Peoria, IL 61604, (2) Department of Biology, Central Michigan University, Brooks 230, Mount Pleasant, MI 48859

Efficient fermentation processes to produce ethanol from low-cost lignocellulosic biomass are sought to support the expansion of the biofuels industry.  Stress-tolerant microorganisms are needed that are able to consume both hexose and pentose sugars and also withstand, survive, and function in the presence of stress factors common to fermentations of lignocellulose hydrolysates, including inhibitors such as furfural, hydroxymethylfurfural (HMF), and ethanol.  Furfural and HMF are key byproducts of the dilute-acid hydrolysis pretreatment of lignocellulosic biomass, the most economical method of releasing hemicellulosic sugars for fermentation to ethanol biofuel.  Our research has shown that natural strains of the yeasts Saccharomyces cerevisiae and Pichia stipitis can survive and adapt to the presence of furfural and HMF and that this survival could be linked in part to a fully functioning pentose phosphate pathway.   Data will be presented showing that mineral and nitrogen source composition had significant impact on the ability of P. stiptis to survive and detoxify furan inhibitors and to convert high xylose concentrations efficiently to ethanol.  The culture age and carbon source type (whether glucose or xylose) also influenced inhibitor tolerance and nutritional needs.  Implications of these findings on process-based strategies to produce a tolerant initial population and then to foster and sustain tolerance during growth and ethanol fermentation will be considered.