(311f) Metabolic Engineering of Clostridium Thermocellum to Produce Isobutyl Esters from Lignocellulose

Direct fermentation of lignocellulosic biomass for value-added chemical production is promising for an environmentally sustainable and economically competitive biorefinery. Clostridium thermocellum is a thermophilic bacterium that has a strong capability of fermenting lignocellulose, but its metabolism has mostly been studied to produce short-chain biofuels such as ethanol. Here, we will present metabolic engineering of C. thermocellum to produce medium chain isobutyl esters (i.e., isobutyl acetate, and isobutyl isobutyrate) from lignocellulose. Push-and-pull metabolic engineering strategies involving deletion of the competitive esterase pathway and overexpression of ester production pathway improved the ester production more than 100-folds. This ester biosynthesis platform takes advantages of elevated operation temperature benefiting the in situ separation of the volatile ester products and hence enabling an advanced consolidated bioprocessing platform where hydrolytic enzyme production, cellulose hydrolysis, fermentation, and product separation can take place in a single step.