Development of high-speed and highly efficient butanol production systems from butyric acid with high density of living cells of Clostridium saccharoperbutylacetonicum.

Living cells are alive and have the butanol-producing ability but not much proliferation under nitrogen source-limited condition. We investigated various butanol production systems with high density of living cells of Clostridium saccharoperbutylacetonicum N1-4 supplemented with methyl viologen (MV) as an electron carrier and nutrient dosing for activity regeneration. In continuous butanol production with high density of living cells, butanol yield was drastically increased from 0.365 C-mol/C-mol with growing cells to 0.528 C-mol/C-mol at a dilution rate of 0.85 h⁻¹, being increased with the butanol to total solvent ratio. This yield was increased to 0.591 C-mol/C-mol by adding 0.01 mM MV. MV addition increased not only butanol yield but also butanol concentration and productivity as compared to those without MV addition. However, living cells lost their activity with incubation time, which lowered the operational stability of the system. Therefore, to maintain constant stability, activity regeneration was carried out with high density of living cells and MV. This system produced butanol at high concentration (9.40 g l⁻¹) and productivity (7.99 g l⁻¹ h⁻¹) for approximately 100 h with maintenance of considerably high yield of butanol (0.686 C-mol/C-mol). Thus, we established a high-speed and highly efficient butanol production system.