Mechanism of Propionic Acid Formation by Propionibacterium pentosaceum

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Abstract
Manometric measurements demonstrated that washed, buffered (pH 5.2) suspensions of R. pentosaceum, equilibrated with N2 (30 C), evolved CO2 at rates which decreased in the following order of substrates (Equimolar concns.): pyruvate, succinate, fumarate, malate. The distributions of a series of molarities of propionic and acetic acids between water and ether were employed to construct standard curves from which the molar concns. of each of the 2 acids in a mixture could be measured. Simultaneous, separate fermentations of equal concns. of pyruvate and succinate yielded data which support a scheme for the fermentation of pyruvic acid to acetic and propionic acids, via oxalacetic, malic, fumaric, and succinic acids, a decarboxylation of succinic acid yielding propionic acid, the over-all equation being: 3CH3COCOOH + H2O-+2CH3COOH + CH3CH2OOH + 2CO2 The optimal pH range for the succinic decarboxylase system was 5.1 to 5.2. Malonate (0.3 M) inhibited 90% of the latter''s function and, in the presence of pyruvate, only traces of propionate were found.