Methylation of Halogenated Phenols and Thiophenols by Cell Extracts of Gram-Positive and Gram-Negative Bacteria

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O-methylation of 2,6-dibromophenol was studied in cell extracts prepared from Rhodococcus sp. strain 1395. O-methylation activity was enhanced by the addition of S-adenosyl-l-methionine but was not affected by the addition of 5-methyltetrahydrofolate nor by up to 10 mM MgCl2 or EDTA. By using 2,6-dibromophenol, 4,5,6-trichloroguaiacol, and pentachlorothiophenol as the substrates, O-methylation activity was also demonstrated in extracts from two other Rhodococcus sp. strains, an Acinetobacter sp. strain, and a Pseudomonas sp. strain. A diverse range of chloro- and bromophenols, chlorothiophenols, chloro- and bromoguaiacols, and chloro- and bromocatechols were assayed as the substrates by using extracts prepared from strain 1395; all of the compounds were methylated to the corresponding anisoles, veratroles, or guaiacols, which have been identified previously from experiments using whole cells. The specific activity of the enzyme towards the thiophenols was significantly higher than it was towards all the other substrates—high activity was found with pentafluorothiophenol, although the activity with pentafluorophenol was undetectable with the incubation times used. For the chlorophenols, the position of the substituents was of cardinal importance. The enzyme had higher activity towards the halogenated catechols than towards the corresponding guaiacols, and selective O-methylation of the 3,4,5-trihalogenocatechols yielded predominantly the 3,4,5-trihalogenoguaiacols. As in experiments with whole cells, neither 2,4-dinitrophenol, hexachlorophene, nor 5-chloro- or 5-bromovanillin was O-methylated. The results showed conclusively that the methylation reactions were enzymatic and confirmed the conclusion from extensive studies using whole cells that methylation of halogenated phenols may be a significant alternative to biodegradation.

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