Tracer Studies on the Role of Acetic Acid and Carbon Dioxide in the Fermentation of Lactate by Clostridium lacto-acetophilum.

In a previous study of the fermentation of lactate by Clostridium lacto-acetophilum (Bhat and Barker, 1947) it was shown that pure cultures of this organism can decompose lactate only when acetate is provided as a second substrate, whereas enrichment cultures of the same organism do not require added acetate. This difference in nutritional requirements indicated a corresponding difference in the catabolic processes occurring in the two types of cultures. In pure cultures, lactate and acetate disappeared while butyric acid, carbon dioxide, and hydrogen were formed, whereas in enrichment cultures lactate was decomposed with the formation of acetate in addition to the other products. It is also significant that the yield of carbon dioxide was much lower in the enrichment cultures. The reduced yield of carbon dioxide taken in conjunction with the formation of acetate indicated that the organisms in the enrichment cultures were using carbon dioxide as an oxidant and were converting it to acetic acid. In pure cultures the high yield of carbon dioxide and the requirement for acetate indicated that the bacteria were unable to reduce carbon dioxide in this way. The tracer experiments described in the present paper were designed to provide a direct test of the conclusions derived from the above-mentioned nutritional and metabolic experiments.