Kouji Kawashima

Isolation and characterization of bacterium degrading Tris (1,3-dichloro-2-propyl) phosphate, a persistent organophosphorus compound

Ryo-hei YAMADA, Yoshio KERA, Shouji TAKAHASHI


Tris (1,3-dichloro-2-propyl) phosphate (TDCPP), a typical chlorinated organophosphate triesters, have been used worldwide as flame-retardants and plasticizers, and thus resulting in its dispersion into natural environment. However, there is no informations on the microbial degradation of TDCPP. Because this molecule is known to possess carcinogenicity, mutagenicity and neurotoxicity, there have been concerns about residues of TDCPP in natural environment. Recently, we succeed in obtaining the mixed culture capable of degrading of TDCPP by an enrichment culture method using TDCPP as a sole phosphorus source. The aim of this study is to analyze the mixed culture, and to isolate and characterize TDCPP-degrading bacterium.

In the presence of a good phosphorous source, NaH2PO4, chloride ion release was significantly increased although degradation of TDCPP was slightly repressed. Moreover, the addition of NaH2PO4 also increased the dechlorination of 1,3-dichloro-2-propanol (1,3-DCP), a putative metabolite of TDCPP. Denaturing gradient gel electrophoresis (DGGE) pattern of the mixed culture demonstrated that the increased in of dechlorination ability is caused by changing the microbial population. A TDCPP-degrading bacterium was isolated by limiting dilution assay using medium containing TDCPP as a sole phosphorus source. The 16S rRNA gene sequence of the strain showed the highest identity with those of Sphingomonas trueperi, suggesting that the strain is a member of the genus Sphingomonas.

�@The strain converted TDCPP to 1,3-DCP, which accumulated in the medium. This showed that the strain did not have the 1,3-DCP-degrading ability.

The strain grew on TDCPP, Tris (2-chloroethyl) phosphate, Tris (2,3-dibromopropyl) phosphate, Triphenyl phosphate and Tricresyl phosphate as a sole phosphorus source. However, the strain was not able to grow on the Trimethyl phosphate, Triethyl phosphate, Tributyl phosphate, Tris (2-ethylhexyl) phosphate and Tris (butoxyethyl) phosphate.