Degradation of aromatic compounds by Acinetobacter radioresistens S13: growth characteristics on single substrates and mixtures.

Acinetobacter radioresistens S13 is able to grow on phenol or benzoate as the sole carbon and energy source: both these compounds are catabolized through the beta-ketoadipate pathway. Genes encoding the catabolic enzymes for degradation of aromatic compounds are localized on A. radioresistens S13 chromosome and organized in, at least, two distinct sets, one for benzoate degradation and another for phenol catabolism. In the present study, the growth and biodegradation kinetics for benzoate and phenol, and an easily metabolized substrate (acetate) were established. Benzoate was degraded slower and supports a less rapid and efficient growth than either acetate or phenol. A combined transcript-proteomic analysis of some of the major catabolic genes and their products nonetheless has shown that benzoate induces the expression of both benzoate and phenol catabolic operons. This result was confirmed by the fact that benzoate-acclimatized bacteria were rapidly able to degrade phenol too. Finally, the growth and biodegradation kinetics for different mixtures of acetate, benzoate and phenol were determined. Results indicate that a hierarchy of substrate utilization, benzoate > acetate > phenol, occurred: benzoate was the preferred substrate, despite its lower growth and biodegradation parameters. Hypotheses explaining these unusual metabolic features of A. radioresistens S13 are discussed.