2.2 Batch fermentation
Batch fermentation in serum bottles and bioreactors was conducted to evaluate the effect of butyric acid on the growth of C. acetobutylicum ATCC55025. Each bottle containing 100 ml of P2 medium with 20 g/L glucose and various amounts of butyric acid at an initial concentration of 0, 2, 5, or 10 g/L was inoculated with 3 mL of 24-h active culture and incubated at 37 oC without shaking. Liquid samples were withdrawn from the bottles periodically to monitor changes in the cell density by measuring the optical density at 600 nm (OD600). Batch fermentation was also conducted in a 500-mL stirred-tank bioreactor containing 250 mL P2 medium with ~50 g/L glucose and 4 g/L butyric acid as the carbon sources. The reactor pH was controlled at ~5.0 with ammonium hydroxide (20% w/v). Liquid samples were withdrawn periodically for analyses of cell (optical density, OD600), glucose, butyric and acetic acids, and solvents (acetone, butanol, and ethanol).