Complete detoxification of tris(2-chloroethyl) phosphate by two bacterial strains: Sphingobium sp. strain TCM1 and Xanthobacter autotrophicus strain GJ10

Tris(2-chloroethyl) phosphate (TCEP), a flame retardant, is recently regarded as a potentially toxic and persistent environmental contaminant. We previously isolated TCEP-degrading bacterium, Sphingobium sp. strain TCM1, which, however, produced a toxic metabolite: 2-chloroethanol (2-CE). This study was undertaken to develop a detoxification technique of TCEP using strain TCM1 with a 2-CE-degrading bacterium: Xanthobacter autotrophicus strain GJ10. TCEP degradation by strain TCM1-resting cells was thermally stable for 30 min at 30°C. It was optimal at 30°C and at pH 8.5. In the optimum condition, TCM1 cells up to a final cell density of 0.8 at OD660 in the reaction mixture were unable to hydrolyze the phosphotriester bonds of 10 μM TCEP completely. The addition of 50 μM Co2+ to reaction mixture enhanced the hydrolysis and caused the complete hydrolysis at the cell density of 0.8. Strain GJ10 resting cells degraded 2-CE only slightly, which might be attributable to lack of coenzyme regeneration of enzymes involved in the degradation. In contrast, the growing cells degraded approximately 180 μM of 2-CE within 24 h. Based on these results, we designed a two-step TCEP detoxification reaction consisting of TCEP hydrolysis to 2-CE by strain TCM1-resting cells and the following degradation of the resulting 2-CE by strain GJ10-growing cells. The combined reaction completely detoxified 10 μM TCEP, and thus opens a way to microbial detoxification of the potential toxic, persistent organophosphorus compound.