S143: Production of bio-ethanol from lignocellulosic materials through engineering yeast cell surface and metabolic pathway

Numerous environmental and social benefits could result from the replacement of petroleum-based transport fuels with bio-fuels converted from lignocellulosic materials. For the utilization of the materials, we have developed a cell surface engineering system that displays various kinds of functional proteins on the surface of microbes without loss of their activities. The display of cellulolytic enzymes (endoglucanase, cellobiohydrolase, and β–glucosidase) on the surface of Saccharomyces cerevisiae has successfully produced ethanol directly from amorphous cellulose. Since the yeast is reusable by collecting the cells, the system has advantages on the process integration of enzyme hydrolysis and fermentation. Also, for the efficient production of ethanol from lignocellulosic materials, the improvement of not only fermentation ability but also tolerance to fermentation inhibitors present in lignocellulosic hydrolysates is required for the S. cerevisiae strain to be used. The hydrolysates contain high concentrations of inhibitors (e.g., acetic acid, formic acid and furan derivatives) that negatively affect metabolism and ethanol yields. To circumvent the difficulties, we have aimed to breed robust S. cerevisiae strains that efficiently consume sugars in the presence of the inhibitors through metabolic engineering. In the present study, the effect of acetic acid on xylose fermentation was determined with a metabolic profiling technique, which revealed that the enhancement of metabolic flux of pentose phosphate pathway is important for the improvement of ethanol productivity in the presence of acetic acid.