Kazuya HIROKAWA

Isolation of a Chlorinated Organophosphoric Acid Triester-Degrading Microorganism

Ryo-hei YAMADA, Yoshio KERA, Shouji TAKAHASHI


Organophosphoric acid triesters have been widely used as flame retardants, plasticiser, hydraulic fluids and pesticides and have been produced in large quantities. The compounds are therefore widely distributed in the natural environment. Some of them are known to have acute toxicities , mutagenicity and neurotoxicity, similar to those of organophosphorous pesticides. Although chlorinated triesters such as tris(1,3-dichloro-2-propyl)phosphate (TDCPP) and tris(2-chloroethyl)phosphate are highly toxic among them, there is no information on the microbial degradation of these chlorinated triesters. The aim of this study is to isolate and characterize TDCPP-degrading microorganisms.

An enrichment culture method using TDCPP as a sole carbon source was employed to isolate TDCPP-degrading microorganisms from soil samples. Eight strains isolated from soils in the city of Nagaoka were found to decrease TDCPP added to the culture medium. One of the isolates, strain No.18 that reduced TDCPP most effectively was further examined and found to release chloride ion to the medium. However, the amount of chloride ion released appeared larger than that expected from the decrease of TDCPP, indicating a remaining question. The 16S rRNA gene sequence of the strain showed the highest identity with those of Acinetobacter sp., suggesting that the strain is a member of the genus Acinetobacter. The strain could utilize ethanol as a sole carbon source but not glucose. Addition of ethanol to the medium stimulated the growth of the strain , but abolished the decrease of TDCPP, which, in contrast, was not affected by addition of phosphate. These findings suggest that TDCPP was indeed used as a source of carbon and not phosphate when it was consumed. It remains to be a task for the future to show clearly that the bacterium in fact degrades the compound.