Isobutanol production at elevated temperatures in thermophilic Geobacillus thermoglucosidasius

The potential advantages of biological production of chemicals or fuels from biomass at high temperatures include reduced enzyme loading for cellulose degradation, decreased chance of contamination, and lower product separation cost. In general, high temperature production of compounds that are not native to the thermophilic hosts is limited by enzyme stability and the lack of suitable expression systems. Further complications can arise when the pathway includes a volatile intermediate. Here we report the engineering of Geobacillus thermoglucosidasius to produce isobutanol at 50 °C. We prospected various enzymes in the isobutanol synthesis pathway and characterized their thermostabilities. We also constructed an expression system based on the lactate dehydrogenase promoter from Geobacillus thermodenitrificans. With the best enzyme combination and the expression system, 3.3 g/l of isobutanol was produced from glucose and 0.6 g/l of isobutanol from cellobiose in G. thermoglucosidasius within 48 h at 50 °C. This is the first demonstration of isobutanol production in recombinant bacteria at an elevated temperature.