Effective utilization of all sugars in cellulosic hydrolysate during fermentation is essential in keeping cellulosic feedstocks a competitive source for various bioconversions including ethanol production. Saccharomyces cerevisiae has long been recognized as a promising microorganism for ethanol fermentation. Recent successes in metabolic engineering enable the strain to utilize xylose as a carbon source, thus allowing co-fermentation of glucose and xylose in cellulosic hydrolysate. However, xylose utilization was found to be bottleneck in ethanol production through co-fermentation of corn-stover hydrolysate at low starting cell density presumably due to inhibitors present in cellulosic hydrolysate.

Hence, we are evaluating the effects of fermentation inhibitors on xylose utilization in co-fermentation. As for possible solutions to increase xylose utilization, the studies on how nutrient supplementation and starting cell density affect xylose utilization are conducted on laboratory media. In addition, similar strategies would be tested in cellulosic hydrolysate derived from AFEX-treated corn stover, DDGS and switchgrass at high solids loading saccharification. These studies are conducted using Saccharomyces cerevisiae 424A(LNH-ST), a genetically-engineered ethanologen for co-fermentation of glucose and xylose.