Anaerobic Biotransformation of Six Representative Organohalogen Contaminants by a Dehalogenimonas-Rich Consortium: Kinetics, Metabolic Pathways, and Reciprocal Effects in Binary Mixtures

Although Dehalogenimonas is as prevalent as Dehalococcoides across organohalide-contaminated habitats, its catalytic capacity and substrate profile toward diverse carbon skeletons and halogen substituents remain largely unexplored. Here, we systematically investigated the anaerobic biotransformation of six representative halogenated organic pollutants by a Dehalogenimonas-rich consortium (QY2-S1). Single-exposure assays revealed marked kinetic divergence spanning an order of magnitude, with 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE, 3.91 ± 0.34 d−1) > β-1,2,5,6-tetrabromocyclooctane (β-TBCO, 2.35 ± 0.13 d−1) > 2,2′,4,4′,5-pentabromodiphenyl ether (BDE 99, 1.31 ± 0.09 d−1) > 1,1,1,3,10,11-hexachloroundecane (a short-chain chlorinated paraffin [SCCP] congener, 0.15 ± 0.01 d−1) > 2,2′,3,3′,6,6′-hexachlorobiphenyl (PCB 136, 0.11 ± 0.01 d−1), whereas tris(2-chloroethyl) phosphate (TCEP) remained untransformed. Transformation kinetics might be primarily governed by carbon–halogen bond dissociation energies and carbon skeleton geometry, with aliphatic and brominated compounds exhibiting faster transformation rates than aromatic and chlorinated analogues. Under binary co-exposures, competitive inhibition varied from reciprocal kinetic attenuation (in BDE 99 & β-TBCO and DPTE & β-TBCO pairs) to pronounced asymmetry (in PCB 136 & BDE 99 and PCB 136 & 1,1,1,3,10,11-hexachloroundecane pairs), whereas TCEP completely halted PCB 136 dechlorination. Product identification revealed that the Dehalogenimonas-rich consortium facilitated ortho-regioselective debromination of BDE 99, concurrent aromatic debromination and side-chain dihalo-elimination/dehydrobromination of DPTE, reductive dechlorination/dehydrochlorination of the SCCPs, and dibromo-elimination coupled with epoxidation of β-TBCO. These findings provide critical insights into the environmental fate and bioremediation potential of organohalide mixtures in anoxic environments.