The Mechanism of the Butanol-acetone Fermentation

The question whether pyruvic acid holds a key position as an intermediate in the butanol-acetone fermentation by Clostridium acetobutylicum (Weizmann) similar to that in the alcoholic fermentation by yeast and in glycolysis by muscle has, so far, not received a decisive answer. This is mainly due to the inconsistent results obtained by different workers in this field. As in the case of corn-meal and glucose, the dissimilation of pyruvic acid should lead to the same products, viz., butanol, butyric acid, ethanol, acetic acid, acetone, and isopropanol respectively. A number of authors, Johnson et al. (l), Langlykke et al. (2), Brown et al. (3), Osburn et al. (4), and Davies et al. (5, S), did obtain butyl products and acetone from pyruvic acid as the sole substrate or from mixed fermentations with glucose, but the yields were poor. On the other hand, Koepsell and Johnson (7, 8) and Simon (9, lo), using dried or washed cell preparations of Clostridium butylicum or C. acetobutylicum, found acetic acid to be the only dissimilation product, even in the presence of glucose. Acetic acid was added as a labeled compound to fermenting corn mash. Wood, Brown, and Werkman (11) thus found that both isotopic butanol and acetone were formed in good yields. These authors suggested, therefore, that both butanol and acetone are derived from a common precursor and discussed the possibility of the following sequence of reactions: acetate -+ pyruvate --+ butyl products and acetone. The regular formation of ethanol, a normal and independent dissimilation product in the butanol-acetone fermentation, stresses the importance of pyruvic acid as a possible intermediate. Its r&e as precursor of butyl products and acetone made a reinvestigation desirable. The present paper deals with the study of the experimental conditions which lead from pyruvate to butyl products and acetone with yields comparable to those obtained from both corn mash and glucose.