Hexabromocyclododecanes (HBCDs) are widely used brominated flame retardants that cause antidiuretic hormone syndrome and even induce cancer. However, little information is available about the degradation mechanisms of HBCDs. In this study, genomic and proteomic analyses, reverse transcription-quantitative PCR, and gene knockout assays reveal that a cytochrome P450-encoding gene is responsible for HBCD catabolism in Pseudomonas aeruginosa HS9. The CO difference spectrum of the enzyme CYP168A1 was matched to P450 characteristics via UV visibility. We demonstrate that the reactions of debromination and hydrogenation are carried out one after another based on detection of the metabolites pentabromocyclododecanols (PBCDOHs), tetrabromocyclododecadiols (TBCDDOHs), and bromide ion. In the 18O isotope experiments, PBCD18OHs were only detected in the H218O group, proving that the added oxygen is derived from H2O, not from O2. This study elucidates the degradation mechanism of HBCDs by Pseudomonas. IMPORTANCE Hexabromocyclododecanes (HBCDs) are environmental pollutants that are widely used in industry. In this study, we identified and characterized a novel key dehalogenase, CYP168A1, that is responsible for HBCD degradation from Pseudomonas aeruginosa strain HS9. This study provides new insights into understanding biodegradation of HBCDs.
Keywords: biodegradation; cytochrome P450; hexabromocyclododecanes; mechanism.