Cellulosic alcoholic fermentation using recombinant Saccharomyces cerevisiae engineered for the production of Clostridium cellulovorans endoglucanase and Saccharomycopsis fibuligera β-glucosidase

In this study, Saccharomyces cerevisiae was engineered for simultaneous saccharification and fermentation of cellulose by the overexpression of the endoglucanase D (EngD) from Clostridium cellulovorans and the beta-glucosidase (Bgl1) from Saccharomycopsis fibuligera. To promote secretion of the two enzymes, the genes were fused to the secretion signal of the S. cerevisiae alpha mating factor gene. The recombinant developed yeast could produce ethanol through simultaneous production of sufficient extracellular endoglucanase and beta-glucosidase. When direct ethanol fermentation from 20 g L-1 beta-glucan as a substrate was performed with our recombinant strains, the ethanol concentration reached 9.15 g L-1 after 50 h of fermentation. The conversion ratio of ethanol from beta-glucan was 80.3% of the theoretical ethanol concentration produced from 20 g L-1 beta-glucan. In conclusion, we have demonstrated the construction of a yeast strain capable of conversion of a cellulosic substrate to ethanol, representing significant progress towards the realization of processing of cellulosic biomass in a consolidated bioprocessing configuration.