The bacterial oxidation of phenylacetic acid.

The bacterial oxidation of aromatic compounds closely related in chemical structure may proceed by different pathways. Thus, while the main features of the breakdown of mandelic acid are established, those of phenylacetate are not, except insofar as it is known to follow a different route (Stanier, 1950). The divergencies may possibly indicate a difference in the mode of ring fission; and since it is established that mandelic acid and certain other aromatic compounds give rise to ,-ketoadipic acid (Kilby, 1948, 1951; Stanier, 1950), we have investigated the production of keto acids in phenylacetate metabolism. At the same time we have attempted to determine whether the reactions of the tricarboxylic acid cycle play a part in these oxidations, and whether there is any evidence under favorable conditions for an abridged cycle as postulated by Barron, Ardao, and Hearon (1950) for Corynebacterium creatinovorans and termed by them the "dicarboxylic acid cycle". Pyruvic acid accumulates in aerated cultures of Aerobacter aerogenes growing on glucose or various dicarboxylic acids only when its rate of production exceeds the demands of logarithmic growth, while shortly after cell division ceases its presence may no longer be detected (Dagley et al., 1951). Since conditions in a growing or fully grown culture may not favor detection of metabolic intermediates, we have followed keto acid production by nonproliferating suspensions aerated in media from which the source of nitrogen has been omitted. Under such conditions the concentration of keto acids in the medium rises initially, attains a maximum, and then declines eventually to zero when the rate of decomposition exceeds the rate of formation. In studies of keto acid production, therefore, it is essential to conduct kinetic investigations over a period of time defined by the position of the concentration maximlum.