Enhanced butanol production by modulation of electron flow in Clostridium acetobutylicum B3 immobilized by surface adsorption.

The objective of this study was to improve butanol yield and productivity by redox modulation and immobilization of Clostridium acetobutylicum B3 cells. Stoichiometric network analysis revealed that NAD(P)H that had escaped from the fermentation as H2 limited the butanol yield and led to the accumulation of oxidation byproducts, e.g., acetone. Methyl viologen was used as an electron carrier to divert the electron flow away from H2 production and to reinforce the NAD(P)H supply. Butanol yield was increased by 37.8% with severely diminished acetone production. Immobilization of the cells by adsorption onto a fibrous matrix improved their butanol tolerance and production rate. An average of 15.6 g/L butanol was achieved within 12 h with a solvent productivity of 1.88 g/L/h in repeated batch fermentation. To our knowledge, this is the highest solvent productivity with a relatively high butanol titer produced by a Clostridium strain in batch fermentation.