Development Of A Consolidated Bioprocessing For Ethanol Production From Sugarcane Bagasse By Co-culturing Of Three Recombinant Saccharomyces Cerevisiae Strains

To degrade lignocellulose for producing fuel ethanol as an alternative of thepetroleum energy is of great interest to researchers. Bagasse, which is abundant andlow-cost, has great prospect of exploitation and application as raw materials for fuelethanol. In this study, a consolidated bioprocessing (CBP) was established byco-culturing three recombinant strains of Saccharomyces cerevisiae whichrespectively expressed one of the three cellulases to convert ethanol from bagasse.The CBP was optimized and the efficiency of ethanol production was investigated inthe thesis.The three recombinant strains of Saccharomyces cerevisiae respectivelyexpressed endoglucanase III, cellobiohydrolase II, and β-glucosidase I fromTrichoderma viride. In the co-culturing system, the EGIII、CBHII and BGLI activitieswere0.445IU/mL、0.016IU/mL and0.732IU/mL, respectively. The synergisticenzyme activity (filter paper activity, FPA) of the three cellulases reached0.083FPA/mL.To optimize the CBP, the effects of different sizes of bagasse, concentration ofthe components of the fermentation medium, and different inoculation ratio onethanol yield were investigated in this study. The results indicated that ethanol yieldwas increased when smaller particle of bagasse was employed. However, consideringthe balance of energy consumption and ethanol yield,200mesh of bagasse waschosen as raw material for the CBP. According to the L9orthogonal test, the optimalcombination of fermentation medium was150g/L bagasse,28g/L CSL,7g/L(NH4)2SO4, and4g/L KH2PO4. Furthermore, the synergistic enzyme activity (FPA)reached the maximum value when the volume ratio of EGIII、CBHII and BGLI was1:3:2.Based on the optimal conditions mentioned above, the CBP was performed in3 L fermenter with the inoculation proportions of1:1:1and1:3:2respectively. Theresults indicated that the ethanol yield of the latter was20.26g/L (or59.6%oftheoretical value),3.15g/L higher than that of the former. The consumption rate of thebagasse was74.1%, which was higher than that of equal volume inoculation.In conclusion, the CBP of producing bio-ethanol from bagasse was successfullyestablished by co-culturing the three recombinant strains of Saccharomyces cerevisiae,although there is also some space to improve the ethanol yield.