5-46: Evaluation of simultaneous saccharification and fermentation and consolidated bioprocessing of steam exploded sugarcane bagasse by different cellulolytic, hemicellulolytic and xylose fermenting recombinant Saccharomyces cerevisiae strains

Significant efforts are being directed towards the reduction of the amount of enzyme needed to complete the lignocellulose saccharification. In this context, consolidated bioprocessing (CBP), where the production of saccharolytic enzymes, hydrolysis of the polysaccharides and the fermentation steps are basically carried out by a single microorganism in the same reactor, is regarded as a potential step forward for low cost biomass processing.

In this work, the hydrolytic and fermenting performance of recombinant Saccharomyces cerevisiae strains co-expressing several cellulases and xylanases during CBP were evaluated in steam treated sugarcane bagasse. Subsequently, an enzyme mixture consisting of cellulase and ß-glucosidase was used to supplement enzyme activities expressed by the recombinant strains in a SSF process. Results showed that the recombinant yeast strains were able to hydrolyse and ferment the pretreated sugarcane bagasse but with low ethanol yields. The addition of a conventional enzyme dosage during SSF with recombinant strains provided an increment up to 10% in the ethanol yield compared with the parental strain. As expected, these differences were more evident when reducing the enzyme loading. In conclusion, although the concept of CBP of steam pretreated bagasse was proven to be feasible, there is still a need of external enzyme supplementation to equal the ethanol yield obtained by the parental strain. The reconstruction of cellulolytic and hemicellulolytic enzyme systems in more robust industrial strains will be needed to improve CBP performance.