Simultaneous Expression of an Endogenous Spermidine Synthase and a Butanol Dehydrogenase from Thermoanaerobacter pseudethanolicus in Clostridium thermocellum Results in Increased Resistance to Acetic Acid and Furans, Increased Ethanol Production and an Increase in Thermotolerance: Article No. 46

Sensitivity to inhibitors derived from the pretreatment of plant biomass is a barrier to the consolidated bioprocessing of these complex substrates to fuels and chemicals by microbes. Spermidine is a low molecular weight aliphatic nitrogen compound ubiquitous in microorganisms, plants, and animals and is often associated with tolerance to stress. We recently showed that overexpression of the endogenous spermidine synthase enhanced tolerance of the Gram-positive bacterium, Clostridium thermocellum to the furan derivatives furfural and HMF. Here we show that co-expression with an NADPH-dependent heat-stable butanol dehydrogenase from Thermoanaerobacter pseudethanolicus further enhanced tolerance to furans and acetic acid and most strikingly resulted in an increase in thermotolerance at 65 degrees C. Tolerance to fermentation inhibitors will facilitate the use of plant biomass substrates by thermophiles in general and this organism in particular. The ability to grow C. thermocellum at 65 degrees C has profound implications for metabolic engineering.