Trichloroethylene oxidation by the membrane-associated methane monooxygenase in type I,type II and type X methanotrophs |
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Authors: | Alan A DiSpirito Jay Gulledge Andrew K Shiemke J Colin Murrell Mary E Lidstrom Cinder L Krema |
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Institution: | (1) Department of Microbiology, Immunology and Preventive Medicine, Iowa State University, 50011 Ames, Iowa, USA;(2) Dept of Biology, University of Texas at Arlington, 76019 Arlington, TX, USA;(3) Dept of Biochemistry, West Virginia University, 26506 Morgantown, WV, USA;(4) Dept of Biological Sciences, University of Warwick, CV4 7AL Coventry, UK;(5) Environmental Engineering Science California Institute of Technology, 91125 Pasadena, CA, USA |
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Abstract: | Trichloroethylene (TCE) oxidation was examined in 9 different methanotrophs grown under conditions favoring expression of the membrane associated methane monooxygenase. Depending on the strain, TCE oxidation rates varied from 1 to 677 pmol/min/mg cell protein. Levels of TCE in the reaction mixture were reduced to below 40 nmolar in some strains. Cells incubated in the presence of acetylene, a selective methane monooxygenase inhibitor, did not oxidize TCE.Cultures actively oxidizing TCE were monitored for the presence of the soluble methane monooxygenase (sMMO) and membrane associated enzyme (pMMO). Transmission electron micrographs revealed the cultures always contained the internal membrane systems characteristic of cells expressing the pMMO. Naphthalene oxidation by whole cells, or by the cell free, soluble or membrane fractions was never observed. SDS denaturing gels of the membrane fraction showed the polypeptides associated with the pMMO. Cells exposed to 14C-acetylene showed one labeled band at 26 kDa, and this protein was observed in the membrane fraction. In the one strain examined by EPR spectroscopy, the membrane fraction of TCE oxidizing cells showed the copper complexes characteristic of the pMMO. Lastly, most of the strains tested showed no hybridization to sMMO gene probes. These findings show that the pMMO is capable of TCE oxidation; although the rates are lower than those observed for the sMMO. |
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Keywords: | methanotrophs membrane associated methane monooxygenase trichloroethylene oxidation |
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