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Applied and Environmental Microbiology, November 1999, p. 5035-5041, Vol. 65, No. 11
0099-2240/99/$04.00+0

Oxidation of Methyl Halides by the Facultative Methylotroph Strain IMB-1

Jeffra K. Schaefer and Ronald S. Oremland*

U.S. Geological Survey, Menlo Park, California 94025

Received 4 May 1999/Accepted 27 August 1999

Washed cell suspensions of the facultative methylotroph strain IMB-1 grown on methyl bromide (MeBr) were able to consume methyl chloride (MeCl) and methyl iodide (MeI) as well as MeBr. Consumption of >100 µM MeBr by cells grown on glucose, acetate, or monomethylamine required induction. Induction was inhibited by chloramphenicol. However, cells had a constitutive ability to consume low concentrations (<20 nM) of MeBr. Glucose-grown cells were able to readily oxidize [14C]formaldehyde to 14CO2 but had only a small capacity for oxidation of [14C]methanol. Preincubation of cells with MeBr did not affect either activity, but MeBr-induced cells had a greater capacity for [14C]MeBr oxidation than did cells without preincubation. Consumption of MeBr was inhibited by MeI, and MeCl consumption was inhibited by MeBr. No inhibition of MeBr consumption occurred with methyl fluoride, propyl iodide, dibromomethane, dichloromethane, or difluoromethane, and in addition cells did not oxidize any of these compounds. Cells displayed Michaelis-Menten kinetics for the various methyl halides, with apparent Ks values of 190, 280, and 6,100 nM for MeBr, MeI, and MeCl, respectively. These results suggest the presence of a single oxidation enzyme system specific for methyl halides (other than methyl fluoride) which runs through formaldehyde to CO2. The ease of induction of methyl halide oxidation in strain IMB-1 should facilitate its mass culture for the purpose of reducing MeBr emissions to the atmosphere from fumigated soils.

* Corresponding author. Mailing address: U.S. Geological Survey, 345 Middlefield Road, MS 480, Menlo Park, CA 94025. Phone: (650) 329-4482. Fax: (650) 329-4463. E-mail: roremlan{at}usgs.gov.

Applied and Environmental Microbiology, November 1999, p. 5035-5041, Vol. 65, No. 11
0099-2240/99/$04.00+0


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