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Methane monooxygenase gene expression mediated by methanobactin in the presence of mineral copper sources

Lookup NU author(s): Dr Charles Knapp, Professor David Graham

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Abstract

Methane is a major greenhouse gas linked to global warming; however, patterns of in situ methane oxidation by methane-oxidizing bacteria (methanotrophs), nature's main biological mechanism for methane suppression, are often inconsistent with laboratory predictions. For example, one would expect a strong relationship between methanotroph ecology and Cu level because methanotrophs require Cu to sustain particulate methane monooxygenase (pMMO), the most efficient enzyme for methane oxidation. However, no correlation has been observed in nature, which is surprising because methane monooxygenase (MMO) gene expression has been unequivocally linked to Cu availability. Here we provide a fundamental explanation for this lack of correlation. We propose that MMO expression in nature is largely controlled by solid-phase Cu geochemistry and the relative ability of Cu acquisition systems in methanotrophs, such as methanobactins (mb), to obtain Cu from mineral sources. To test this hypothesis, RT-PCR expression assays were developed for Methylosinus trichosporium OB3b (which produces mb) to quantify pMMO, soluble MMO (the alternate MMO expressed when Cu is "unavailable"), and 16S-rRNA gene expression under progressively more stringent Cu supply conditions. When Cu was provided as CuCl2, pMMO transcript levels increased significantly consistent with laboratory work. However, when Cu was provided as Cu-doped iron oxide, pMMO transcript levels increased only when mb was also present. Finally, when Cu was provided as Cu-doped borosilicate glass, pMMO transcription patterns varied depending on the ambient mb:Cu supply ratio. Cu geochemistry clearly influences MMO expression in terrestrial systems, and, as such, local Cu mineralogy might provide an explanation for methane oxidation patterns in the natural environment. © 2007 by The National Academy of Sciences of the USA.


Publication metadata

Author(s): Knapp C, Fowle D, Kulczycki E, Roberts J, Graham D

Publication type: Article

Publication status: Published

Journal: Proceedings of the National Academy of Sciences of the United States of America

Year: 2007

Volume: 104

Issue: 29

Pages: 12040-12045

Print publication date: 17/07/2007

ISSN (print): 0027-8424

ISSN (electronic): 1091-6490

URL: http://dx.doi.org/10.1073/pnas.0702879104

DOI: 10.1073/pnas.0702879104

PubMed id: 17615240


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