Critic acid metabolism of Aerobacter aerogenes.

Aerobacter aerogenes is able to utilize citric acid as sole source of carbon for growth in both aerobic and anaerobic conditions. From an analysis of fermentation liquors Deffner and Franke (1939) and Brewer and Werkman (1939) concluded that citric acid is decomposed anaerobically to oxalacetate and acetate as initial products. Manometric studies by the latter workers, using Aerobacter indologenes, showed that oxalacetic, pyruvic, and L-malic acids were fermented readily in addition to citric acid, and they also suggested that the "citrate enzyme" was adaptive rather than constitutive. Ajl and Werkman (1949) observed the effect of bisulfite and other inhibitors on the ability of citrate to replace the CO2 requirement of A. aerogenes and concluded that the aerobic decomposition of citric acid occurs by a different mechanism. Preparation of bacterial extracts which catalyze some of the reactions of the tricarboxylic acid cycle (Korkes et al., 1950; Stone and Wilson, 1952) has established a pathway for citrate oxidation by this mechanism. Krebs (1950) has drawn attention to the possibility that the dissimilation of citrate to oxalacetate and acetate may be a reversal of the synthesis of tricarboxylic acids and accordingly deserves further attention than it has received so far. For unaerated cultures of A. aerogenes relationships between bacterial crop and nutrient concentration are linear for glucose (Dagley et al., 1951) and citrate (Dagley et al., 1953) up to certain concentrations, beyond which further additions of carbon source produce no increase in crop in the presence of excess nitrogen source. Aeration of such cultures results in large increases in crop and further consumption of the source of carbon. Among the suggestions to account for the effect of aeration on glucose cultures is that of Fowler (1951) attributing fermentation to an unspecified adaptive enzyme, inactivated by oxygen. Since the effect of aeration on growth of cultures utilizing glucose and citrate is similar, it was of additional interest to study further the citric acid metabolism of A. aerogenes for which a definite adaptive enzyme has been postulated in anaerobic conditions.