Abstract
In view of the intermediary rôle assigned to pyruvic acid in bacterial metabolism, the mechanism of its breakdown by Lactobacillus lycopersici is of importance to an understanding of the dissimilation of carbohydrates by the heterofermentative lactic acid bacteria.
A medium containing pyruvic acid, peptone, yeast extract and K2HPO4 adjusted to pH 6.2 was fermented anaerobically at 30°C. by L. lycopersici. Formation of the 3 final products in equimolar quantities (Table I) indicates a dissimilation involving oxidation of one molecule of pyruvic acid and the simultaneous reduction of a second. Decarboxylation of pyruvic acid does not appear to occur since fixation of acetaldehyde by dimedon or bisulphite was repeatedly unsuccessful. The close relationship of the lactic bacteria to the propionic bacteria and the failure of van Niel 1 and Wood and Werkman 2 to detect acetaldehyde in fermentations by the latter suggests application of the proposal of these investigators to the lactic acid bacteria, i. e., breakdown of pyruvic acid according to equation (1). The active hydrogen serves to reduce a second molecule to lactic acid.
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