Isotopic Characterization (2H, 13C, 37Cl, 81Br) of the Abiotic Sinks of Methyl Bromide and Methyl Chloride in Water and Implications for Future Studies.

The rates at which methyl chloride, methyl bromide and methyl iodide react with the hydroxyl and the thiosulphate ions in water have been measured at various concentrations and temperatures. The apparent energies of activation in both series increase in the same direction as the dipole moment of the methyl halide. The results are discussed in terms of a theory of the kinetics of the reactions between ions and polar molecules in solution.

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Description of Toluene Inhibition of Methyl Bromide Biodegradation in Seawater and Isolation of a Marine Toluene Oxidizer That Degrades Methyl Bromide

Applied and Environmental Microbiology ◽

10.1128/aem.71.7.3495-3503.2005 ◽

2005 ◽

Vol 71 (7) ◽

pp. 3495-3503 ◽

Cited By ~ 18

Author(s):

Kelly D. Goodwin ◽

Ryszard Tokarczyk ◽

F. Carol Stephens ◽

Eric S. Saltzman

Keyword(s):

Methyl Bromide ◽

Stratospheric Ozone ◽

Methyl Chloride ◽

Inhibitory Effect ◽

Biogeochemical Cycle ◽

Natural Seawater ◽

Methyl Halides ◽

Western Atlantic ◽

The North ◽

Seawater Samples

ABSTRACT Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are important precursors for destruction of stratospheric ozone, and oceanic uptake is an important component of the biogeochemical cycle of these methyl halides. In an effort to identify and characterize the organisms mediating halocarbon biodegradation, we surveyed the effect of potential cometabolic substrates on CH3Br biodegradation using a 13CH3Br incubation technique. Toluene (160 to 200 nM) clearly inhibited CH3Br and CH3Cl degradation in seawater samples from the North Atlantic, North Pacific, and Southern Oceans. Furthermore, a marine bacterium able to co-oxidize CH3Br while growing on toluene was isolated from subtropical Western Atlantic seawater. The bacterium, Oxy6, was also able to oxidize o-xylene and the xylene monooxygenase (XMO) pathway intermediate 3-methylcatechol. Patterns of substrate oxidation, lack of acetylene inhibition, and the inability of the toluene 4-monooxygenase (T4MO)-containing bacterium Pseudomonas mendocina KR1 to degrade CH3Br ruled out participation of the T4MO pathway in Oxy6. Oxy6 also oxidized a variety of toluene (TOL) pathway intermediates such as benzyl alcohol, benzylaldehyde, benzoate, and catechol, but the inability of Pseudomonas putida mt-2 to degrade CH3Br suggested that the TOL pathway might not be responsible for CH3Br biodegradation. Molecular phylogenetic analysis identified Oxy6 to be a member of the family Sphingomonadaceae related to species within the Porphyrobacter genus. Although some Sphingomonadaceae can degrade a variety of xenobiotic compounds, this appears to be the first report of CH3Br degradation for this class of organism. The widespread inhibitory effect of toluene on natural seawater samples and the metabolic capabilities of Oxy6 indicate a possible link between aromatic hydrocarbon utilization and the biogeochemical cycle of methyl halides.

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