Engineering Clostridium Thermocellum to Produce Ethanol from Cellulose at High Yield and Titer

Ethanol is the biofuel produced in the largest amount worldwide.  Clostridium thermocellum is a promising candidate for ethanol production from cellulose due to its native ability to consume cellulose, and thus engineering efforts have focused on methods for improving ethanol production.  To date, we have created over 40 different strains that employ a variety of engineering strategies, however we have only been able to achieve an ethanol yield of 75% of the theoretical maximum and 25 g/l titer.  To allow for further improvements, we suspected that we might need an exogenous ethanol production pathway.  Thermoanaerobacterium saccharolyticum has been engineered to produce ethanol at 90% of the theoretical maximum yield and 70 g/l titer.  We identified the genes responsible for the ethanol production pathway in this organism and transferred the pathway to C. thermocellum.