Production of Ethanol from Corn Stalks Using an Engineered Strain of Saccharomyces Cerevisiae

Cellulosic ethanol has been widely regarded as an attractive alternative fuel, due to the sufficient supply of feedstocks, the rapid advance on pretreatment, and the decreased cost of biomass hydrolysis. Efficient co-utilization of xylose and glucose is critical for cellulosic ethanol production. Recently, many efforts had been made to introduce the xylose metabolic pathways into S. cerevisiae. However, most of the engineered S. cerevisiae strains cannot metabolize xylose well under anaerobic condition. In this study, we engineered S. cerevisiae by introducing xyl1 and xyl2 genes from Pichia stipitis and overexpressing its own xk gene. The engineered strain was subjected to continuous evolution with dissolved oxygen concentration gradually decreased. The resulted adaptive strain, S. cerevisiae W32N55, could efficiently metabolize xylose under static condition, and tolerate the inhibitors in cellulosic hydrolysate. Furthermore, a fermentation-membrane pervaporation coupling process was developed and applied in the fermentation of the hydrolysate of steam exploded corn stalks. Using such a process, the final ethanol concentration reached 70 g/L, with a yield of 220 kg ethanol per ton steam exploded stalks.