Bacterial Metabolism

Carbohydrat,es are fermented by Clostridium acetobutylicum and related microorganisms with the formation of acetic acid, n-butyric acid, acetone, ethanol, and n-butanol. It has been conclusively proved that the butanol arises by the reduction of the butyric acid (1, 2). As yet, however, there is no exact information as to the sequence of reactions by which butyric acid is formed from glucose by such microorganisms, although several investigators have advanced speculative schemes to account for such a transformation. The nature of these schemes has recently been described in a number of reviews (3-6) and need not be considered here, except to note that, with the exception of the hypothesis advanced by Neuberg and Arinstein (7), all of these schemes have followed the early suggestion of Biichner and Meisenheimer (8) that butyric acid is formed in some manner from aldol. The latter is assumed to arise from the condensation of 2 molecules of acetaldehyde formed in turn from the carbohydrate, although as yet neither of these substances has been detected in fermentation induced by butanol-forming microorganisms. In some experiments made several years ago, the writers attempted to determine if such bacteria could utilize either aldol or its dehydration product, crotonic aldehyde. The latter was readily reduced to n-butanol by actively fermenting cultures of Clostriclium acetobutylicum, while aldol proved to be of such great toxicity to the bacteria, that cessation of fermentation invariably followed its addition in even minute amounts to actively fermenting cultjures. In consequence, experiments of this type were