Engineering Clostridium Thermocellum for High Ethanol Yield

Clostridium thermocellum, a gram-positive, thermophilic anaerobic bacterium, is a candidate organism for consolidated bioprocessing, due to its ability to solubilize cellulosic biomass and ferment said biomass into organic acids and ethanol.  There have been several attempts to date to engineer C. thermocellum to produce ethanol at high yield; however, the maximum reported yield is 60% of theoretical.

Our group has previously engineered another thermophilic anaerobe, Thermoanaerobacter saccharolyticum, to produce ethanol at >90% theoretical yield.  We have characterized and identified the genes that play a major role in producing the high ethanol yield, and now seek to transfer the key genes of this pathway into C. thermocellum to improve ethanol production.

In order to do this, we have improved our plasmid-based expression system to use in our organism.  We have used this new plasmid to express adhE, a gene that encodes activities thought to play a role in the last two steps of ethanol production.