Degradation of benzo[a]pyrene by bacterial isolates from human skin

Polycyclic aromatic hydrocarbons (PAHs) are some of the most widespread xenobiotic pollutants, with the potentially carcinogenic high-molecular-weight representatives being of particular interest. However, while in eukaryotes, the cytochrome P450 (CYP)-mediated activation of benzo[a]pyrene (B[a]P) has become a model for metabolism-mediated carcinogenesis, the oxidative degradation of B[a]P by microorganisms is less well studied. This should be reason for concern as the human organ most exposed to environmental PAHs is the skin, which at the same time is habitat to a most diverse population of microbial commensals. Yet, nothing is known about the skin's microbiome potential to metabolise B[a]P. This study now reports on the isolation of 21 B[a]P-degrading microorganisms from human skin, 10 of which were characterised further. All isolates were able to degrade B[a]P as sole source of carbon and energy, and degradation was found to be complete in at least four isolates. Substrate metabolism involved two transcripts that encode a putative DszA/NtaA-like monooxygenase and a NifH-like reductase, respectively. Analysis of the 16S-rRNA genes showed that the B[a]P-degrading isolates comprise Gram⁺ as well as Gram^- skin commensals, with Micrococci being predominant. Moreover, microbial B[a]P-degradation was detected on all volunteers probed, indicating it to be a universal feature of the skin's microbiome.