Direct ethanol production from cassava pulp using a surface-engineered yeast strain co-displaying two amylases, two cellulases, and β-glucosidase

In order to develop a method for producing fuel ethanol from cassava pulp using cell surface engineering (arming) technology, an arming yeast co-displaying alpha-amylase (alpha-AM), glucoamylase, endoglucanase, cellobiohydrase, and beta-glucosidase on the surface of the yeast cells was constructed. The novel yeast strain, possessing the activities of all enzymes, was able to produce ethanol directly from soluble starch, barley beta-glucan, and acid-treated Avicel. Cassava is a major crop in Southeast Asia and used mainly for starch production. In the starch manufacturing process, large amounts of solid wastes, called cassava pulp, are produced. The major components of cassava pulp are starch (approximately 60%) and cellulose fiber (approximately 30%). We attempted simultaneous saccharification and ethanol fermentation of cassava pulp with this arming yeast. During fermentation, ethanol concentration increased as the starch and cellulose fiber substrates contained in the cassava pulp decreased. The results clearly showed that the arming yeast was able to produce ethanol directly from cassava pulp without addition of any hydrolytic enzymes.