Observations on the preferential biodegradation of selected components of polyaromatic hydrocarbon mixtures

The capacity of the naphthalene degrading enzyme (NAH) system of Pseudomonas fluorescens 5R and a number of other NAH system bacterial isolates to degrade mixtures of polyaromatic hydrocarbons (PAHs) and heterocyclic compounds were examined. It was found that all the examined organisms displayed similar patterns of preferential compound degradation when presented with the same mixture. Using strains that possess portions of the NAH system, this preferential degradation was localized to the activity of naphthalene dioxygenase. Comparisons of the first-order rates of compound degradation with the structures of the mixture components indicated that increased deviation from the base structure of naphthalene led to slower disappearance. Structural features that were found to decrease the rate of compound degradation include an increase in the number of methyl substituents and an increase in the size of a substituent.