Biodehalogenation: Rapid oxidative metabolism of mono- and polyhalomethanes by Methylosinus trichosporium OB-3b

Resting cells of Methylosinus trichosporium OB-3b grown in the absence of copper salts rapidly oxidize mono- and polyhalomethanes. The order of reactivity of the series is CH3X > CH2X2 ≥ CHX3 (X = CI, Br). Based on halide ion release, the half-life for methyl bromide and methyl chloride is 9.4 min with a cell density of 0.1 g/ml. The dihalomethanes and bromo-form react at the same rate and half as rapidly as the methyl halides. Chloroform is converted to carbon dioxide at one-fourth the methyl halide rate (t1/2 = 38 min). No isotope effect was observed with either deuteromethylene chloride or deuterochloro-form (CD2Cl2, CDCl3). In all cases, the dehalogenation chemically follows an oxygen insertion into the CH bond, and the final product is carbon dioxide (HCO3−). All reactions are inhibited by acetylene, establishing methane monooxygenase as the responsible enzyme. Incubations with 13CHCl3, 13CH2Br2, and 13CH3Br and nuclear magnetic resonance (NMR) analysis of reaction mixtures showed the first hydrolytically stable products from CHCl3 (HCO3−) and CH2Br2 (CO), but neither formaldehyde nor formate could be detected as intermediates with methyl bromide by this method. The oxidative destruction of halo-methanes by this methylotroph is rapid and not very sensitive to structure.