Reductive dehalogenation by diverse microbes is central to biogeochemical cycles in deep-sea cold seeps

Reductive dehalogenation is crucial for halogen cycling and environmental remediation, yet its ecological role is not completely understood, especially in deep-sea environments. To address this gap, we investigated the diversity of reductive dehalogenases (RDases) and ecophysiology of organohalide reducers in deep-sea cold seeps, which are environments rich in halogenated compounds. Through genome- resolved metagenomic analysis of 165 global cold seep sediment samples, we identified four types of RDases, namely prototypical respiratory, transmembrane respiratory, and cytosolic RDases, and one novel clade. Cold seeps were found to harbor a higher abundance of these RDase genes compared to other marine sediments, establishing them as unique hotspots for microbial reductive dehalogenation activity. These RDases are encoded by a wide range of microorganisms across four archaeal and 36 bacterial phyla, significantly expanding the known diversity of organohalide reducers. Halogen geochemistry, laboratory incubations with various halogenated compounds, metatranscriptomic data, and metabolomic profiling confirmed the presence of organohalides at concentrations of up to 18 mg/g in these sediments and demonstrated their active microbial reduction. This process is tightly linked to other biogeochemical cycles, including carbon, hydrogen, nitrogen, sulfur, and trace elements. RDases from cold seeps have diverse N-terminal structures across different gene groups, and reductive dehalogenase genes in these environments are mostly functionally constrained and conserved. These findings collectively suggest that reductive dehalogenation is a central process in deep-sea environments, mediated by a diverse array of microbes and novel enzymes.