Methylation and Hydroxylation of Pentachiorophenol by Mycobacterium sp. Isolated from Soil

Abstract

Metabolism of pentachlorophenol (PCP) by Mycobacterium sp. which was isolated from soil, and converted PCP to pentachloroanisole (PCA) and partly to tetrachloro-1, 4-dimethoxybenzene (TCHD) was further studied. When washed cell suspension of the isolate was incubated with PCP in a mineral salt medium, tetrachlorocatechol (TCC), tetrachlorohydroquinone (TCHQ), tetrachloro-2-methoxyphenol (TCCM), and tetrachloro-4-methoxyphenol (TCHM) were detected in the benzene extracts from the incubation medium by GC after acetylation, besides PCA and TCHD. Tetrachloro-1, 2-dimethoxybenzene (TCCD) was also detected in the eluates after column chromatography from the benzene extracts. These metabolites were confirmed by mass spectra with GC-MS and by IR spectra after separation and purification by column and/or thin layer chromatography. Mycobacterium sp. converted TCHQ to TCHD via TCHM by successive methylation. TCC was also converted to TCCD via TCCM by this isolate. It was concluded from these results that Mycobacterium sp. metabolized PCP mostly through the methylation and at the same time part of PCP was hydroxylated at ortho and para positions to the hydroxyl group followed by successive methylation. Maximum rate of the methylation was observed between pH 6.5 and 7.0. The hydroxylation, however, was dominant below pH 6.0. The addition of nutrients into the incubation medium resulted in enhancement of the methylation and exclusive formation of PCA as a sole metabolite. Toxicity of PCA for Mycobacterium sp. and for germinating rice seeds was significantly low compared with PCP.