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Microorganisms 2015, 3(2), 290-309; doi:10.3390/microorganisms3020290

Methane Oxidation and Molecular Characterization of Methanotrophs from a Former Mercury Mine Impoundment

Geological Survey, Menlo Park, CA 94025, USA
Department of Earth System Science, Stanford University, Stanford, CA 94305, USA
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Author to whom correspondence should be addressed.
Academic Editors: Marina G. Kalyuzhnaya and Ludmila Chistoserdova
Received: 29 April 2015 / Revised: 1 June 2015 / Accepted: 11 June 2015 / Published: 23 June 2015
(This article belongs to the Special Issue Microbial C1 Metabolism)
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The Herman Pit, once a mercury mine, is an impoundment located in an active geothermal area. Its acidic waters are permeated by hundreds of gas seeps. One seep was sampled and found to be composed of mostly CO2 with some CH4 present. The δ13CH4 value suggested a complex origin for the methane: i.e., a thermogenic component plus a biological methanogenic portion. The relatively 12C-enriched CO2 suggested a reworking of the ebullitive methane by methanotrophic bacteria. Therefore, we tested bottom sediments for their ability to consume methane by conducting aerobic incubations of slurried materials. Methane was removed from the headspace of live slurries, and subsequent additions of methane resulted in faster removal rates. This activity could be transferred to an artificial, acidic medium, indicating the presence of acidophilic or acid-tolerant methanotrophs, the latter reinforced by the observation of maximum activity at pH = 4.5 with incubated slurries. A successful extraction of sterol and hopanoid lipids characteristic of methanotrophs was achieved, and their abundances greatly increased with increased sediment methane consumption. DNA extracted from methane-oxidizing enrichment cultures was amplified and sequenced for pmoA genes that aligned with methanotrophic members of the Gammaproteobacteria. An enrichment culture was established that grew in an acidic (pH 4.5) medium via methane oxidation. View Full-Text
Keywords: acid mine drainage; methane stable isotopes; methanotrophic bacteria; sterols; hopanoids acid mine drainage; methane stable isotopes; methanotrophic bacteria; sterols; hopanoids

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Baesman, S.M.; Miller, L.G.; Wei, J.H.; Cho, Y.; Matys, E.D.; Summons, R.E.; Welander, P.V.; Oremland, R.S. Methane Oxidation and Molecular Characterization of Methanotrophs from a Former Mercury Mine Impoundment. Microorganisms 2015, 3, 290-309.

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