Glucose production from cellulose through biological simultaneous enzyme production and saccharification using recombinant bacteria expressing the β-glucosidase gene

Efficient cellulosic biomass saccharification technologies are required to meet biorefinery standards. Biological simultaneous enzyme production and saccharification (BSES), which is glucose production from cellulosic biomass by Clostridium thermocellum , can be a reliable cellulose saccharification technology for biorefineries. However, the current BSES processes require purified β-glucosidase supplementation. In this study, recombinant bacteria expressing the β-glucosidase gene were developed and directly applied to BSES. The engineered Escherichia coli expressing the thermostable β-glucosidase gene from Thermoanaerobacter brockii exhibited 0.5 U/ml of β-glucosidase activities. The signal peptide sequence of lytF gene from Bacillus subtilis was the most appropriate for the β-glucosidase secretion from Brevibacillus choshinensis , and the broth exhibited 0.74 U/ml of β-glucosidase activities. The engineered E. coli and B. choshinensis expressing the thermostable β-glucosidase gene produced 47.4 g/L glucose and 49.4 g/L glucose, respectively. Glucose was produced by the hydrolysis of 100 g/L Avicel cellulose for 10 days through BSES, and the product yield was similar to that obtained through BSES with purified β-glucosidase supplementation. Our findings indicate that the direct supplementation of β-glucosidase using bacterial cells expressing β-glucosidase gene or their broth was applicable to BSES, suggesting the potential of this process as a cost-effective approach to cellulose saccharification.