Metabolic engineering of Thermobifida fusca for direct aerobic bioconversion of untreated lignocellulosic biomass to 1-propanol

Biofuel production from renewable resources can potentially address lots of social, economic and environmental issues but an efficient production method has yet to be established. Combinations of different starting materials, organisms and target fuels have been explored with the conversion of cellulose to higher alcohols (1-propanol, 1-butanol) being one potential target. In this study we demonstrate the direct conversion of untreated plant biomass to 1-propanol in aerobic growth conditions using an engineered strain of the actinobacterium, Thermobifida fusca. Based upon computational predictions, a bifunctional butyraldehyde/alcohol dehydrogenase was added to T. fusca leading to 1-propanol production during growth on glucose, cellobiose, cellulose, switchgrass and corn stover. The highest 1-propanol titer (0.48 g/L) was achieved for growth on switchgrass. These results represent the first demonstration of direct conversion of untreated lignocellulosic biomass to 1-propanol in an aerobic organism and illustrate the potential utility of T. fusca as an aerobic, cellulolytic bioprocess organism.

► Pathway from succinyl-CoA to propanoyl-CoA was found by computational predictions and verified by RT-PCR and enzymatic assays in Thermobifida fusca.
► A bifunctional butyraldehyde/alcohol dehydrogenase gene (adhE2) from Clostridium acetobutylicum was inserted into the chromosome DNA in T. fusca forming B6 strain.
► B6 strain was able to directly convert raw untreated switchgrass and corn stover to 1-propanol aerobically.