Tris(2-chloroethyl) and tris(1,3-dichloro-2-propyl) phosphates are chlorinated persistent flame retardants that have recently emerged as environmental pollutants. Two bacterial strains that can degrade the compounds when they are the sole phosphorus sources have been isolated and identified as members of the sphingomonads. The strains can be useful for the bioremediation of environments contaminated with these compounds.The chlorinated organophosphorus (OP) compounds tris(2-chloroethyl) phosphate (TCEP) and tris(1,3-dichloro-2-propyl) phosphate (TDCPP) are widely used as flame retardants mainly in a range of plastic foams, resins, and latexes and in the production of liquid unsaturated polyester resins, respectively (21). Their widespread use has led to their contamination of various environments, including indoor air and house dust (9, 15), surface water (2), ground water (4), rain and snow (11), and sediment (6), in concentrations ranging from ng/liter up to several g/liter. Particularly, a higher contamination level was observed in leachates and raw water of waste disposal sites (7). Furthermore, they were also detected in drinking water (21) because they are hard to eliminate not only in the environment but also in sewage treatment plants (1). Many studies have shown several toxic effects of the compounds. TCEP has been shown to cause adverse effects on brain, liver, and kidney and on the fertility of male rats and mice (21). In addition, TCEP has produced tumors at various organ sites (19) and has also been suspected to possess carcinogenicity (10); although there are contradictory results on its carcinogenicity (3), TCEP has been shown to inhibit the expression of cell cycle regulatory proteins, DNA synthesis, and cell numbers (12). TDCPP has exhibited genotoxicity in several in vitro assays conducted in prokaryotic and eukaryotic cells (14) and produced some indications of carcinogenicity (21). These observations have prompted the recognition of potential ecological and human health concerns.Many bacteria and fungi capable of degrading OP pesticides and insecticides, such as parathion and chlorpyrifos, have been discovered, isolated, and characterized (13). In contrast, few studies have been conducted on microbial degradation of chlorinated OP flame retardants, despite their persistence and potential, nonnegligible toxicity. Thus far, there has been no report of the isolation of bacteria capable of degrading TCEP and TDCPP.We recently demonstrated that these compounds were rapidly degraded in two enrichment bacterial cultures, named 45D and 67E, obtained by using TCEP and TDCPP as sole phosphorus sources (16). We therefore attempted to isolate bacteria capable of degrading the compounds from each enrichment culture. Five hundred microliters of 45D stored at 4°C was transferred to 100 ml of A-Cl medium containing 20 M TDCPP (Wako Pure Chemical, Japan) as the sole phosphorus source (16). Medium A-Cl is a minimal medium composed of 10 g/liter glucose, 5.22 g/liter 3-morpholinepropanesulfonic acid, 1 g of (NH...