Breeding of industrial diploid yeast strain with chromosomal integration of multiple beta-glucosidase genes.

We constructed a double auxotrophic OC-2 industrial diploid strain of Saccharomyces cerevisiae and introduced 4 copies of cell surface displaying beta-glucosidase (BGL) genes into the chromosome. The engineered OC-2 strain showed 5-fold higher BGL activity compared with the yeast carrying 2 copies of BGL gene and directly produced ethanol from cellobiose.