Dehalobacter-mediated reductive dechlorination of the organophosphorus insecticide chlorpyrifos in mangrove sediments.
Abstract
Mangrove sediments are important sinks for organic contaminants, including the widely used chlorinated organophosphorus insecticide chlorpyrifos (CPF). Although CPF degradation under oxic conditions has been extensively studied, its anaerobic transformation in reducing coastal environments remains poorly understood. Here, a mangrove sediment-derived anaerobic enrichment culture achieved nearly complete transformation of 10 mg L-1 CPF within 10 days. Ultraperformance liquid chromatography-Orbitrap high-resolution mass spectrometry (UPLCOrbitrap-HRMS) revealed the formation of a mono-dechlorinated CPF product, which was tentatively assigned as O,Odiethyl O-(3,5-dichloro-2-pyridinyl) phosphorothioate based on tandem mass spectrometry (MS/MS) evidence and density functional theory (DFT) calculations of C-Cl bond dissociation energies. The enrichment culture also reductively dechlorinated 3,5,6-trichloro-2-pyridinol (TCP), a common CPF transformation product, primarily to 5,6-dichloro-2-pyridinol, with Ecological Structure-Activity Relationships (ECOSAR) modeling predicting lower aquatic toxicity for the dechlorinated products than for their parent compounds. 16S rRNA gene amplicon sequencing and metagenomic analyses revealed marked enrichment of Dehalobacter during active CPF transformation, strongly implicating this organohalide-respiring lineage in CPF dechlorination. A high-quality Dehalobacter metagenome-assembled genome harboring 39 rdhA homologs was recovered. Integrated metatranscriptomic and metaproteomic analyses further prioritized four candidate reductive dehalogenases (CPF-RDH1/2/3/9), with CPF-RDH2 showing the strongest proteomic support. Together, these findings uncover an overlooked anaerobic transformation route of CPF through direct reductive dechlorination and highlight the potential role of Dehalobacter-associated organohalide respiration in the environmental fate of chlorinated organophosphorus contaminants in mangrove sediments.
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