Conversion of Starch into Ethanol by Saccharomyces cerevisiae Strain Transformed with a-Amylase Gene from Rhizopus oryzae

Abstract

The direct production of ethanol from starch by a recombinant Saccharomyces cerevisiae strain, W303-1A, which expressed the Rhizopus oryzae a-amylase gene, was carried out by shakeflask fermentation. The effects of several factors, such as a-amylase activity, inoculum size, initial glucose supply and glucoamylase supplementation, on starch utilization and ethanol production have been investigated. The a-amylase produced by the recombinant strain was sufficient to obtain complete degradation of starch. However, the starch-degradation rate and ethanol-production efficiency were low. In the presence of exogenous glucoamylase in the starchcontaining cultures, the ethanol-production levels of the recombinant strain were significantly improved and the ethanol yields increased up to 3.75 g/L, which was approximately three times higher than that observed for the native strain and the biomass obtained with the recombinant strain was two times that observed for the native strain.