Development of an industrial ethanol-producing yeast strain for efficient utilization of cellobiose.

The BGL1 gene, encoding β-glucosidase in Saccharomycopsis fibuligera, was intracellular, secreted or cell-wall associated expressed in an industrial strain of Saccharomyces cerevisiae. The obtained recombinant strains were studied under aerobic and anaerobic conditions. The results indicated that both the wild type and recombinant strain expressing intracellular β-glucosidase cannot grow in medium using cellobiose as sole carbon source. As for the recombinant EB1 expressing secreted enzyme and WB1 expressing cell-wall associated enzyme, the maximum specific growth rates (μ(max)) could reach 0.03 and 0.05 h(-1) under anaerobic conditions, respectively. Meanwhile, the surface-engineered S. cerevisiae utilized 5.2 g cellobioseL(-1) and produced 2.3 g ethanol L(-1) in 48 h, while S. cerevisiae secreting β-glucosidase into culture broth used 3.6 g cellobiose L(-1) and produced 1.5 g ethanolL(-1) over the same period, but no-full depletion of cellobiose were observed for both the used recombinant strains. The results suggest that S. cerevisiae used in industrial ethanol production is deficient in cellobiose transporter. However, when β-glucoside permease and β-glucosidase were co-expressed in this strain, it could uptake cellobiose and showed higher growth rate (0.11h(-1)) on cellobiose.