With the recent emergence of biofuels as an alternative renewable energy resource to fossil fuels, industries need low-cost processing of biomass into bioethanol, which currently involves several high-cost enzymatic reactions: i) biomass pre-treatment, ii) production of saccharolytic enzymes, iii) hydrolysis of the polysaccharides into fermentable sugars, iii) fermentation of the hexoses and pentoses.

Therefore, the scope of this project is to construct a consolidated bioprocessing-competent strain of Saccharomyces cerevisiae, that could hydrolyse cellulose of the pre-treated biomass into glucose and ferment it to ethanol. Since S. cerevisiae is naturally ethanologenic, but not cellulolytic, three main classes of cellulases are required to be expressed in synergy in the yeast to degrade cellulose : first, endoglucanases (EGL) break down cellulose into cellulodextrins, second, cellobiohydrolases generate cellobioses and soluble cellulodextrins, and last, betaglucosidases (BGL) produce the glucose. We have tested the activity of 37 BGL1s and BGL5s in yeast, on two substrates, p-NPG and cellobiose, showing that only BGL1s are active on both substrates. Furthermore, active BGLs could be grouped in clusters on a dendrogram of the BGLs active domains. Our second best BGL, An1010, was selected for fermentation experiments. Cellobiose fermentation abilities of an anchored and a secreted An1010 were studied. The secreted version performed better than the anchored, with respect to cellobiose utilization and ethanol production. Our next step is to clone this BGL on the chromosome together with an EGL, and improve the strain’s fermentation abilities by genome shuffling.