Identification of alkaline phosphatase genes for utilizing a flame retardant,tris(2-chloroethyl) phosphate,in Sphingobium sp. strain TCM1

Tris(2-chloroethyl) phosphate (TCEP) is a haloalkyl phosphate flame retardant and plasticizer that has been recognized as a global environmental contaminant. Sphingobium sp. strain TCM1 can utilize TCEP as a phosphorus source. To identify the phosphomonoesterase involved in TCEP utilization, we identified four putative alkaline phosphatase (APase) genes, named SbphoA, SbphoD1, SbphoD2, and SbphoX-II, in the genome sequence. Following expression of these genes in Escherichia coli, APase activity was confirmed for the SbphoA and SbphoX-II gene products but was not clearly observed for the SbphoD1 and SbphoD2 gene products, owing to their accumulation in inclusion bodies. The single deletion of either SbphoA or SbphoX-II retarded the growth and reduced the APase activity of strain TCM1 cells on medium containing TCEP as the sole phosphorus source; these changes were more marked in cells with the SbphoX-II gene deletion. In contrast, the deletion of either SbphoD1 or SbphoD2 had no effect on cell growth or APase activity. The double deletion of SbphoA and SbphoX-II resulted in the complete loss of cell growth on TCEP. These results show that SbPhoA and SbPhoX-II are involved in the utilization of TCEP as a phosphorus source and that SbPhoX-II is the major phosphomonoesterase involved in TCEP utilization.