S54: Engineering Saccharomyces cerevisiae for consolidated bioprocessing in starch and biomass conversion

The conversion of starch or biomass to biofuel is a two-stage process involving enzymatic treatment, followed by yeast fermentation.  An alternative route would be to consolidate the process by engineering Saccharomyces cerevisiae capable of both saccharification and fermentation.  An approach was designed to clone multiple genes into the yeast to express and secrete enzyme combinations.  Yeast cloned with mixed gene constructs of alpha-amylase and glucoamylase resulted in the production of these enzymes in active forms with synergistic actions.  The recombinant yeast acquired the capacity of starch hydrolysis reaching 90% conversion on a 4% starch culture.  Ethanol was produced and detected along with the breakdown of starch. Similar strategies to engineer yeast with cellulase, xylanase, and feruloyl esterase genes individually and in combinations also produced active enzymes capable of breaking down their respective substrates.  Studies on employing the yeast for cell-based degradation and fermentation of biomass are in progress.