Isolation and characterization of bacteria degrading chlorinated organophosphate esters, persistent organophosphorus compounds

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Organophosphate esters(OPEs) constitute the predominant group of phosphorus-containing flame-retardants and plasticizers, as well as of agricultural pesticides and herbicides. These OPE flame-retardants and plasticizers are widely used worldwide in diverse materials, such as plastics, polymeric foams, rubbers, textiles and building materials. Among them, chlorinated organophosphate esters, such as tris(2-chloroethyl) phosphate (TCEP) or tris(1,3-dichloro-2-propyl) phosphate (TDCPP) have several toxic effects including carcinogenic and immunotoxic activities. However, microorganisms or enrichment culture capable of readily degrading the chlorinated OPEs have not been reported.In this study, for the first time, we succeed in obtaining two mixed bacterial cultures capable of rapidly degrading both TCEP and TDCPP by enrichment using each compound as the sole phosphorus source, and analyzed their degradation ability and generated metabolites. Then we isolate two bacteria from the mixed bacterial cultures, and identified and designated them as Sphingomonas sp. strain TDK1 and Sphingobium sp. strainTCM1. Both strains can degrade TDCPP and TCEP.In the degradation of TCEP and TDCPP, we detected 2-chloroethanol (2-CE) and 1,3-dichloro-2-propanol (1,3-DCP) as a metabolite by a gas chromatography-mass spectroscopy (GC-MS) analysis, respectively. This is the first report that the chloroalcohols were produced as a metabolite of the chlorinated OPEs by microbial degradation and indicated the cleavage of phosphoester bond in their degradation pathways.The phosphoesterase, the enzyme catalyzing the first step of the degradation of TDCPP and TCEP, were localized the soluble fraction of the bacterial cell. We purified the enzyme 68-fold from cell-free extracts of Sphingobium sp. strainTCM1, to near homogeneity. The enzyme is a monomer and molecular mass was 62.7 kDa.