The deep sea covers more than half of the Earth's surface and plays a crucial role in biogeochemical cycles, serving as one of the major reservoirs of biodiversity. Halogenated organic compounds (HOCs) are a class of recalcitrant organic pollutants that are enriched in marine environments and are widely distributed in deep-sea and hadal ecosystems. Previous studies have demonstrated that dehalogenating microorganisms and associated dehalogenation metabolic pathways are widely distributed in deep-sea environments. In particular, genomes of hadal microorganisms contain abundant genes potentially involved in the degradation of halogenated organic compounds, suggesting that the metabolism of HOCs represents an important component of deep-sea carbon cycling.

Previous studies conducted by our research group have confirmed that hadal microorganisms exhibit high degradation activity toward halogenated organic compounds. Furthermore, we found that members of the phylum Chloroflexi in sediments from the Mariana Trench possess nearly complete metabolic pathways involved in the degradation of polychlorinated biphenyls (PCBs) and organochlorine compounds. However, due to the unique biogeochemical characteristics of hadal environments, the halogen cycling processes mediated by microorganisms in the much larger area of the typical deep-sea environment remain poorly understood.

In this study, two representative halogenated organic compounds, 4-chlorobiphenyl (4-PCB) and γ-hexachlorocyclohexane (γ-HCH), were selected as model substrates. Deep-sea sediment samples collected from the Pacific Ocean at a depth of 3200 m were used to establish sediment-based co-culture systems, which were subsequently incubated under simulated deep-sea environmental conditions. Microorganisms from the enrichment cultures were isolated and cultivated using a single carbon source consisting of representative halogenated organic compounds. Differences among culturable microorganisms obtained under different incubation periods and with different substrates were investigated, and a preliminary culture collection of halogenated organic compound-degrading bacterial strains was established.

Representative bacterial strains were selected for degradation experiments using model halogenated organic compounds. The degradation efficiencies of these compounds were determined by gas chromatography–mass spectrometry (GC/MS), and the underlying degradation mechanisms were further investigated through metabolic analyses. Based on these results, metabolic pathways involved in the degradation of representative halogenated organic compounds were proposed and reconstructed.