Sequential Reductive Dechlorination of Triclosan by Sediment Microbiota Harboring Organohalide-Respiring .

Aquatic ecosystems represent a prominent reservoir of xenobiotic compounds, including triclosan (TCS), a broad-spectrum biocide extensively used in pharmaceuticals and personal care products. As a biogeochemical hotspot, the potential of aquatic sediments for the degradation of TCS remains largely unexplored. Here, we demonstrated anaerobic biotransformation of TCS in a batch microcosm established with freshwater sediment. The initial 43.4 ± 2.2 μM TCS was completely dechlorinated to diclosan, followed by subsequent conversion to 5-chloro-2-phenoxyphenol, a monochlorinated TCS (MCS) congener. Analyses of community profile and population dynamics revealed substrate-specific, temporal-growth of and , which are organohalide-respiring bacteria (OHRB) affiliated with class . growth was linked to the formation of diclosan but not MCS, yielding 3.6 ± 0.4 × 10 cells per μmol chloride released. A significant increase in cells, from 1.5 ± 0.4 × 10 to 1.5 ± 0.3 × 10 mL, only occurred during the reductive dechlorination of diclosan to MCS. OHRB gradually disappeared following consecutive transfers, likely due to the removal of sediment materials with strong adsorption capacity that could alleviate TCS's antimicrobial toxicity. Consequently, a solid-free, functionally stable TCS-dechlorinating consortium was not obtained. Our results provide insights into the microbial determinants controlling the environmental fate of TCS.