(188aq) Butanol Production from Cellulose By Clostridium Cellulovorans adhE2 in a Two-Stage pH-Regulated Fermentation Process

Some clostridial strains can directly utilize cellulose for n-butanol production from lignocellulosic biomass. The goal of this research was to develop engineered cellulolytic clostridial strains for n-butanol production in a consolidated bioprocess. A recombinant plasmid for enhanced butanol production was constructed and transformed into C. cellulovorans. The effects of overexpressing adhE2 on butanol production and cellulose utilization were evaluated in batch fermentations in serum bottles. The medium pH was found to significantly affect cell growth and butanol production by the engineered C. cellulovorans. The activity of acetaldehyde/alcohol dehydrogenase (adhE2), which converts acetyl-CoA and butyryl-CoA to ethanol and butanol, respectively, was highly sensitive to the pH. Consequently, significantly higher alcohols production with reduced acids production was obtained at pH 6.0 compared to pH 6.8. About 2.5 g/L butanol, 2.5 g/L ethanol, 2 g/L butyric acid, and less than 1 g/L acetic acid were produced at pH 6.0. While at pH 6.8, more acids production (>4 g/L acetic acid and >3.6 g/L butyric acid) was observed along with faster cell growth and cellulose consumption. Also, pH 6.0 contributed to a higher C4/C2 ratio of 0.97 g/g (vs. 0.64 g/g at pH6.8). Therefore, a two-stage pH shift strategy was used to optimize cell growth, cellulose utilization, and butanol production in the fermentaion, which showed a great potential for butanol production from cellulose.