Abstract
Mycobacterium sp. strain RJGII‐135 is capable of degrading a wide range of polycyclic aromatic hydrocarbons (PAHs), including benzo[a]pyrene (B__a__P). In this study, critical aspects of degradation were investigated, including compound uptake, relative rates of PAH degradation, and the effects of co‐occurring PAH substrates on B__a__P degradation and mineralization to CO~2~. Mycobacterium sp. strain RJGII‐135 was capable of degrading phenanthrene, anthracene, and pyrene at a 10‐ to 20‐fold greater rate than benz[a]anthracene (B__a__A) and B__a__P. A significant amount of phenanthrene and pyrene, 30% and 10%, respectively, was completely mineralized, whereas less than 4% of anthracene, B__a__A, and B__a__P was mineralized. The PAH uptake assays demonstrated that high amounts of B__a__P and B__a__A, 81% and 75% of added compound, respectively, could be recovered from bacterial cell fractions after a 4‐h incubation compared with pyrene (61%), anthracene (53%), and phenanthrene (47%). The half‐saturation constant (K~m~) for pyrene was threefold lower for pyrene over B__a__P, suggesting that the degradation system in Mycobacterium sp. strain RJGII‐135 has a higher affinity for pyrene, reaching maximal degradative activity at lower concentrations. No hybridization to dioxygenase gene probes __nah__Ac, __bph__A1, or __tol__C1C2 was detected. Studies to investigate competition between different PAH substrates demonstrated that the rate of B__a__P metabolism was influenced by the presence of a second PAH substrate. The B__a__P metabolism was inhibited when coincubated with B__a__A, pyrene, and anthracene. Phenanthrene did not inhibit but enhanced B__a__P metabolism sixfold. These data suggest that induction effects of components of complex mixtures may be as important as competitive metabolism when assessing the ability of bacteria to effectively degrade high‐molecular‐weight PAHs in the environment.