BIODEHALOGENATION: RAPID OXIDATIVE METABOLISM OF MONO- AND POLYHALOMETHANES BY METHYLOSINUS TRICHOSPORIUM OB-3b

Abstract

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 CH,X > CH2X2 2 CHX, (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 bromoform 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 (t,,, = 38 min). No isotope effect was observed with either deuteromethylene chloride or deuterochloroform (CD,C12, CDCI,). In all cases, the dehalogenation chemically follows an oxygen insertion into the C-H bond, and the final product is carbon dioxide (HCO;). All reactions are inhibited by acetylene, establishing methane monooxygenase as the responsible enzyme. Incubations with I3CHCl3, l3CH,Brz, and I3CH3Br and nuclear magnetic resonance (NMR) analysis of reaction mixtures showed the first hydrolytically stable products from CHCI, (HCO;) and CH,Br, (CO), but neither formaldehyde nor formate could be detected as intermediates with methyl bromide by this method. The oxidative destruction of halomethanes by this methylotroph is rapid and not very sensitive to structure.

Spatial variation in natural formation of chloroform in the soils of four coniferous forests

“…The study sites are all characterized by well oxygenated sandy soils (Albers et al, Submitted), and even though anaerobic niches might theoretically occur in the organic top soil after heavy rain events, any degradation that could cause the permanent difference between Hot and Low Spots would be expected to be aerobic. Abiotic degradation of chloroform is known in anoxic sediments (Kenneke and Weber 2003), but no abiotic aerobic pathway for the degradation of chloroform is known and the only known aerobic degradation pathway for chloroform is co-metabolic degradation by various oxygenase-expressing bacteria (Bartnicki and Castro 1994;Alvarez-Cohen et al 1992;Chang and Alvarez-Cohen 1996). This degradation pathway leads to complete mineralization of the chloroform molecule and we therefore performed a mineralization experiment.…”

Oceanic distribution and sources of bromoform and dibromomethane in the Mauritanian upwelling

“…[5] Losses of the brominated methane compounds from the oceanic mixed layer include physical air-sea exchange and turbulent mixing (half-lives of days to weeks [Quack and Wallace, 2003;Quack et al, 2004]), with slower chemical conversion losses from hydrolysis (half-lives of 183 years for CH 2 Br 2 and 686 years for CHBr 3 [Mabey and Mill, 1978]) and halogen exchange (half-live of 5 -74 years for CHBr 3 [Geen, 1992]) as well as biodegradation under aerobic and anaerobic conditions [Bouwer and McCarty, 1983;Bartnicki and Castro, 1994;Goodwin et al, 1997]. CHBr 3 has generally longer lifetimes compared to CH 2 Br 2 in the oceanic environment and only the rate of reduction is faster for CHBr 3 than for CH 2 Br 2 [Vogel et al, 1987].…”

Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds

“…The reactions involve cooxidation of the lower chlorinated methanes with the oxygenases produced to oxidize the primary substrates. CM is cooxidized by Methylosinus trichosporium (Bartnicki & Castro 1994) and Methylococcus capsulatus (Stirling & Dalton 1979) with methane as the primary substrate and by a butane-oxidizing enrichment culture (Kim et al 2000). With Methylosinus trichosporium, a half-life of 9.5 min for CM was reported with a cell density of 100 g wet weight l )1 .…”