Although chlorinated organophosphate esters (Cl-OPEs) have been reported to be ubiquitously distributed in various anoxic environments, little information is available on their fate under anoxic conditions. In this study, we report two Dehalococcoides-containing enrichment cultures that transformed 3.88 ± 0.22 μmol tris(2-chloroethyl) phosphate (TCEP) and 2.61 ± 0.02 μmol tris(1-chloro-2-propyl) phosphate (TCPP) within 10 days. Based on the identification of the transformed products and deuteration experiments, we inferred that TCEP may be transformed to generate bis(2-chloroethyl) phosphate and ethene via one-electron transfer (radical mechanism), followed by C-O bond cleavage. Ethene was subsequently reduced to ethane. Similarly, TCPP was transformed to form bis(1-chloro-2-propyl) phosphate and propene. 16S rRNA gene amplicon sequencing and quantitative polymerase chain reaction analysis revealed that Dehalococcoides was the predominant contributor to the transformation of TCEP and TCPP. Two draft genomes of Dehalococcoides assembled from the metagenomes of the TCEP- and TCPP-transforming enrichment cultures contained 14 and 15 putative reductive dehalogenase (rdh) genes, respectively. Most of these rdh genes were actively transcribed, suggesting that they might contribute to the transformation of TCEP and TCPP. Taken together, this study provides insights into the role of Dehalococcoides during the transformation of representative Cl-OPEs.
Keywords: Dehalococcoides; chlorinated organophosphate esters; reductive dehalogenases; transformation.