The role of acids on the production of acetone and butanol by Clostridium acetobutylicum

Summary The production of solvent by Clostridium acetobutylicum was studied, using fed-batch fermentations. Different specific rates of carbohydrate utilisation were obtained by variations in feeding rates of sugar. At slow catabolic rates of sugar, addition of acetic acid or butyric acid, alone or together, increased the rate of the metabolic transition by a factor 10 to 20, the amount of solvents by a factor 6 and the percentage of fermented glucose to solvents by a factor 3. The same results were obtained with both glucose and xylose fermentations. Depending on the rates of growth, butanol production began at acid levels of 3–4 g·l^-1 for fast metabolism and at acid levels of 8–10 g·l^-1 for slow metabolism. Associated with slow metabolism, reassimilation of acids required values as high as 6.5 g·l^-1 of acetic acid and 7.5 g·l^-1 of butyric acid. At a high rate of metabolism, acetic and butyric acids were reassimilated at concentrations of 4.5 g·l^-1.