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Geochemical mechanisms of copper acquisition by methanotrophic microorganisms

English title Geochemical mechanisms of copper acquisition by methanotrophic microorganisms
Applicant Kretzschmar Ruben
Number 113737
Funding scheme Project funding (Div. I-III)
Research institution Institut für Biogeochemie und Schadstoffdynamik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Pedology
Start/End 01.04.2007 - 31.05.2010
Approved amount 159'263.00
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Keywords (14)

methane oxidation; methanotrophs; nutrient limitation; copper acquisition; chalkophores; methane monooxygenase; soil pollution; heavy metals; zinc; speciation; EXAFS; extraction; adsorption; precipitation

Lay Summary (English)

Lead
Lay summary
Methane is a potent greenhouse gas and increasing atmospheric methane fluxes by more than 65% relative to pre-industrial levels are of particular concern in the context of future global climate change. Changing atmospheric methane concentrations may also have had an important impact on the climate in the earth history. Therefore, the factors controlling methane production and oxidation are under intense investigation. An important source of methane to the atmosphere is methane production by anaerobic methanogenic microorganisms in wetlands, rice fields, and lakes. However, a large fraction of the total methane production by methanogenic organisms is oxidized by anaerobic or aerobic methanotrophic (i.e. methane oxidizing) bacteria. These organisms play therefore a key role in the regulation of methane release to the atmosphere.The inorganic oxidation of methane by oxygen is kinetically hindered. Bacteria catalyze the oxidation of methane to methanol by the particulate methane monooxigenase (pMMO). Some methanotrophs can alternatively express the less efficient soluble methane monooxigenase (sMMO). pMMO contains several copper atoms that are most likely involved in electron transfer to the substrate. Consequently, methane oxidation by pMMO critically depends on the availability of copper and the efficiency of copper acquisition strategies by methanotrophic organism.Recent studies have elucidated a copper acquisition mechanism involving the synthesis of a copper specific ligand (so-called chalkophore) and the exudation of the chalkophore into the extracellular space. Cu(II) is bound by the chalkophore and rapidly reduced to Cu(I), presumably by an intramolecular charge transfer. The binding of Cu(I) obtains high specificity and stability to the Cu-chalkophore complex. This is prerequisite for acquiring Cu in wetlands and sediments containing natural organic matter including humic acids that have a very high affinity for Cu.The hypothesis of this project is that the availability of Cu in soils, wetlands (including bogs and rice paddies etc.), and potentially in the water column of lakes and marine waters is controlled by thermodynamically and kinetically stable complexes with humic substances. Therefore, we propose to measure the stability of the Cu-chalkophore complex, to study the thermodynamic aspects of the competition between humic acids and the chalkophore, and to observe the kinetics of the ligand exchange reaction. We will develop quantitative models for Cu speciation and rate laws for the exchange reactions in the presence of the competing ligands. In a second part of this study we wish to investigate if the low availability of Cu limits methane oxidation in wetland soils. Here, we propose to conduct Cu fertilization using soil samples from a Swiss peat bog. We will investigate the response of biological methane oxidation to Cu speciation and availability and investigate the effect of Cu availability on methanotrophic communities using fluorescent in situ hybridization techniques. The proposed research is important in the context of global carbon cycling and climate controls. It will contribute to the understanding of key factors that control methane release to the atmosphere. Furthermore, the study will enhance our understanding of high affinity nutrient acquisition processes in general.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Competitive ligand exchange between Cu-humic acid complexes and methanobactin
Pesch M. -L., Hoffmann M., Christl I., Kraemer S. M., Kretzschmar R. (2013), Competitive ligand exchange between Cu-humic acid complexes and methanobactin, in GEOBIOLOGY, 11(1), 44-54.
Copper complexation of methanobactin isolated from Methylosinus trichosporium OB3b: pH-dependent speciation and modeling
Pesch Marie-Laure, Christl Iso, Hoffmann Martin, Kraemer Stephan M., Kretzschmar Ruben (2012), Copper complexation of methanobactin isolated from Methylosinus trichosporium OB3b: pH-dependent speciation and modeling, in JOURNAL OF INORGANIC BIOCHEMISTRY, 116, 55-62.
Isolation and purification of Cu-free methanobactin from Methylosinus trichosporium OB3b
Pesch ML, Christl I, Barmettler K, Kraemer SM, Kretzschmar R (2011), Isolation and purification of Cu-free methanobactin from Methylosinus trichosporium OB3b, in GEOCHEMICAL TRANSACTIONS, 12, 2-9.

Associated projects

Number Title Start Funding scheme
129502 Geochemical mechanisms of copper acquisition by methanotrophic microorganisms 01.06.2010 Project funding (Div. I-III)
127157 Coprecipitates of hydrous ferric oxide and natural organic matter: properties and biogeochemical reactivity 01.08.2010 Project funding (Div. I-III)

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