(390e) Recombinant Yeast Strains towards Consolidated Bioprecessing: Surface Display of Functional Mini-Cellulosomes for Direct Conversion of Cellulose to Ethanol | AIChE

(390e) Recombinant Yeast Strains towards Consolidated Bioprecessing: Surface Display of Functional Mini-Cellulosomes for Direct Conversion of Cellulose to Ethanol

Authors 

Wen, F. - Presenter, University of Illinois at Urbana-Champaign
Sun, J. - Presenter, University of Illinois at Urbana-Champaign


Lignocellulosic biofuels represent a sustainable, renewable, and the only foreseeable alternative energy source to transportation fossil fuels. However, the recalcitrant crystalline structure of cellulosic biomass, which endows plant cell walls with resistance to biodegradation, has impeded biological production of cellulosic ethanol. The rate-limiting step in cellulosic ethanol production is the conversion of cellulose to ethanol. The current prevailing strategy to overcome this difficult step involves enzymatic hydrolysis of cellulose to glucose followed by fermentation using ethanogenic microorganisms, such as yeast S. cerevisiae. However, the high cost of producing large amounts of cellulases has made the cellulosic ethanol too expensive to compete with gasoline in the market. Therefore, consolidated bioprocessing (CBP), which combines enzyme production, cellulose hydrolysis, and fermentation in a single step, has been proposed to significantly lower the cellulosic ethanol production cost. Unfortunately, the great potential of CBP cannot be realized using microorganisms available today since they can not simultaneously break down cellulose to glucose and ferment it into ethanol.

In an effort to develop a CBP-enabling microorganism, we engineered a recombinant cellulolytic yeast strain by displaying mini-cellulosome on the surface. The mini-cellulosome is formed by co-expressing a mini-scaffoldin derived from C. thermocellum and three types of cellulases - an endoglucanase, a cellobiohydrolase, and a beta-glucosidase. And the multi-enzyme complex is tethered to the yeast cell surface using the a-agglutinin adhesion receptor. The surface expression of the mini-cellulosome was confirmed and each type of cellulases in the mini-cellulosome showed respective enzymatic activity using various detection methods. Furthermore, the mini-cellulosome showed both enzyme-enzyme synergy and enzyme proximity synergy, and it was stable at 4 C for at least four months. More importantly, yeast cells displaying the mini-cellulosome could directly convert amorphous cellulose to ethanol; and they also showed activity towards crystalline cellulose. The evaluation of ethanol production from crystalline cellulose is in progress.