Development of Complex Cellulosomes On the Yeast Surface for Cellulosic Ethanol Production

The development of alternative energy technology is critically important due to the economy, security and environmental issues. Bioconversion of biomass, the only domestic, sustainable, and renewable energy resource, has significant advantages over other alternative strategies. However, the high cost of overcoming the recalcitrance of the biomass has so far been the primary obstacle impeding the market of biofuels. Enormous efforts have been made for developing cost-effective processes for converting cellulosic biomass into liquid fuels. One of the promising methods is the use of a complexed cellulase system known as the cellulosome, it is found on the surface of many anaerobes in nature. Cellulsomes are composed of a scaffoldin that contains a powerful cellulose-binding module (CBM) and several cohesins which tightly bind to the complementary dockerins in the catalytic subunits. Compared to the noncellulosomal system, the celluolsome exhibits much greater degradative potential due to its highly ordered structure that enables substrate targeting and enzyme proximity synergy. In this study, we created a highly ordered complex cellulosome structure on the yeast surface, which can control the position and ratio of each enzyme in the cellulosome structure. A dramatic and nonlinear enhancement in enzyme activity with the increasing complexity of cellulosome structures was observed, resulting in the improvement of ethanol production. This result strongly suggested that higher enzymatic synergy can be employed to reduce the amount of enzyme needed, leading to a substantial reduction in the cost of biofuel production.