Expressing β-glucosidase from Saccharomycopsis fibuligera in industrial ethanol producing yeast and evaluation of the expressing sufficiency

Abstract

Recombinant β-glucosidase-expressing strains were constructed by integrating different copies of the BGL1 gene from Saccharomycopsis fibuligera into the chromosome of an industrial ethanol-producing strain of Saccharomyces cerevisiae. The engineered strains were evaluated for ethanol fermentation using cellobiose as sole carbon source. The results showed that most of the recombinant β-glucosidase produced by S. cerevisiae was secreted to the cell periplasm, with only a relatively small percentage released into the culture supernatant. Successful and unsuccessful utilization of cellobiose by the recombinant strains was determined by the copy number of BGL1 incorporated into the genome, which was related to specific β-glucosidase activity. Recombinant strain containing at least four copies of BGL1 produced 0.45 U ml−1 extracellularly, combined with 0.96 U mg−1 dry cell weight (DCW) cell pellet of β-glucosidase activity that could hydrolyze cellobiose effectively. Anaerobic growth (0.16 h−1) up to 0.82 g l−1 DCW of the engineered yeast was observed in medium containing 20 g l−1 cellobiose as sole carbohydrate source with concomitant ethanol production of up to 9.7 g l−1. This strain thus represents a promising alternative for efficient and cost-effective ethanol production.