Buffering as a means for increasing growth and butanol production byClostridium acetobutylicum

The objective of this work was to optimize butanol formation in the acetone-butanol-ethanol (ABE) fermentation by examining the level of buffering as it affects the dissociation of butyric acid to the less toxic butyrate anion. Experiments were carried out in batch culture using chemically defined (P2) or complex media containing various buffering agents. These included salts of acetate, citrate, phosphate, nitrate, or bicarbonate, representing a range of pKa values and buffering capacities. Growth in highly buffered medium was found to increase the stationary phase cell density, carbohydrate utilization, and the final butanol concentration. At higher levels of buffering, increased growth and elevated concentrations of butyric acid were required to initiate solventogenesis, suggesting the involvement of a critical threshold level of undissociated butyric acid.