Biotransformation of benzo[a]pyrene by Pannonibacter sp. JPA3 and the degradation mechanism through the initially oxidized benzo[a]pyrene-4,5-dihydrodiol to downstream metabolites

Owing to its adverse effects on the environment and human health, benzo[a]pyrene (BaP) has attracted considerable attention and has been used as a model compound in ecotoxicology. In this study, Pannonibacter sp. JPA3 as a BaP-degrading strain was isolated from the production water of an oil well. The strain could remove 80% of BaP at an initial concentration of 100 mg L-1 after 35 d culture. The BaP-4,5-dihydrodiol, BaP-4,5-epoxide, 5-hydroxychrysene, and 2-hydroxy-1-naphthoic acid metabolites were identified in the biodegradation process. Simultaneously, the gene sequence coding for dioxygenase in the strain was amplified and a dioxygenase model was built by homology modeling. Combined with the identification of the metabolites, the interaction mechanism of BaP with dioxygenase was investigated using molecular docking. It was assumed that BaP was initially oxidized at the C-4-C-5 positions in the active cavity of dioxygenase. Moreover, a hypothesis for the progressive degradation mechanism of BaP by this strain was proposed via the identification of the downstream metabolites. In conclusion, our study provided an efficient BaP degrader and a comprehensive reference for the study of the degradation mechanism in terms of the degrading metabolites and theoretical research at the molecular level.