Simultaneous saccharification and fermentation of acid-pretreated corncobs with a recombinant Saccharomyces cerevisiae expressing β-glucosidase

To reduce the cellobiose inhibition of exoglucanase and endogulcanase and enhance cellulose hydrolysis during simultaneous saccharification and fermentation (SSF), a β-glucosidase encoding gene named BGL1 was cloned from Saccharomycopsis fibuligera and integrated into the chromosomal rDNA region of the Saccharomyces cerevisiae industrial strain NAN-27 producing NAN-227. Compared with the parental strain, which had no detectable activity, the β-glucosidase specific activity in NAN-227 was 1.02 IU/mg of protein. When cellobiose was used as the sole carbon source in a shake-flask, NAN-227 consumed 6.2 g/L of cellobiose and produced 3.3 g/L of ethanol in 48 h. The yield was 0.532 g/g. The parent strain only consumed 1.92 g/L of cellobiose and no ethanol was detected. During the SSF of acid-pretreated corncobs NAN-227 produced 20 g/L of ethanol at 72 h, which was similar to the parent strain when 20 IU of β-glucosidase/g of substrate was added.