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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 129502
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 01.06.2010 - 31.05.2011
Approved amount 62'712.00
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Keywords (10)

methane oxidation; methanotrophs; nutrient limitation; copper acquisition; chalkophores; methane monooxygenase; humic substance; metal exchange; ligand exchange; kinetics

Lay Summary (English)

Lead
Lay summary
Methane is an important greenhouse gas and of particular interest in the context of global climate change. A large fraction of methane produced by methanogenic organisms in wetlands is metabolized by anaerobic or aerobic methanotrophic (i.e. methane oxidizing) bacteria. The oxygen dependent microbial oxidation of methane to methanol is catalyzed by methane monooxigenase (MMO). In contrast to the less efficient soluble methane monooxigenase (sMMO) expressed by some methanotrophs, the particulate methane monooxigenase (pMMO) contains several copper atoms that play a critical role in the reactivity of the enzyme. Therefore, methane oxidation by pMMO is hypothesized to strongly depend on the availability of copper and the efficiency of copper acquisition strategies by methanotrophic organism. Recent studies have elucidated a copper acquisition mechanism of methanotrophs involving the synthesis of a strong copper specific ligand (so-called chalkophore) and the exudation of the chalkophore into the extracellular space. The release of chalkophores may be prerequisite for acquiring Cu in wetlands and sediments containing natural organic matter including humic acids that have a very high affinity for Cu.The aim of this project is to elucidate whether copper availability controlled by natural organic matter is a key factor in the regulation of methane oxidation. During the first part of the project, the chalkophore methanobactin produced by Methylosinus trichosporium OB3b has successfully been isolated from the nutrient medium. The second part will focus on equilibrium exchange experiments to study the kinetics of ligand exchange reactions. The results of these ligand exchange experiments are essential to understand how copper complexation by natural organic matter may affect methane oxidation in wetlands. This 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 Marie-Laure, Christl Iso, Barmettler Kurt, Kraemer Stephan M, Kretzschmar Ruben (2011), Isolation and purification of Cu-free methanobactin from Methylosinus trichosporium OB3b., in Geochemical transactions, 12, 2-2.

Collaboration

Group / person Country
Types of collaboration
Prof. Stephan Kraemer Austria (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Associated projects

Number Title Start Funding scheme
113737 Geochemical mechanisms of copper acquisition by methanotrophic microorganisms 01.04.2007 Project funding (Div. I-III)

Abstract

Methane is an important greenhouse gas and of particular interest in the context of global climate change. Atmospheric methane fluxes have increased by more than 65% relative to pre-industrial levels. Methane production by anaerobic methanogenic microorganisms in wetlands, rice fields, and lakes is considered the major source of atmospheric methane. The inorganic oxidation of methane by oxygen is kinetically hindered. However, a large fraction of methane produced by methanogenic organisms is metabolized by anaerobic or aerobic methanotrophic (i.e. methane oxidizing) bacteria. Therefore, methanotrophic organisms play a key role in the regulation of methane release to the atmosphere.The oxygen dependent microbial oxidation of methane to methanol is catalyzed by methane monooxigenase (MMO). In contrast to the less efficient soluble methane monooxigenase (sMMO) expressed by some methanotrophs, the particulate methane monooxigenase (pMMO) contains several copper atoms that play a critical role in the reactivity of the enzyme. Therefore, methane oxidation by pMMO is hypothesized to strongly depend on the availability of copper and the efficiency of copper acquisition strategies by methanotrophic organism. Recent studies have elucidated a copper acquisition mechanism of methanotrophs involving the synthesis of a strong copper specific ligand (so-called chalkophore) and the exudation of the chalkophore into the extracellular space. The release of chalkophores may be prerequisite for acquiring Cu in wetlands and sediments containing natural organic matter including humic acids that have a very high affinity for Cu.In a current SNF project (No. 200021-113737), we are investigating the stability of Cu-chalkophore complexes and the thermodynamic aspects of the competition between humic acids and chalkophores. The aim of the project is to elucidate whether copper availability controlled by natural organic matter is a key factor in the regulation of methane oxidation. During the first part of this project, the chalkophore methanobactin produced by Methylosinus trichosporium OB3b has successfully been isolated from the nutrient medium. In contrast to recent literature suggesting a simple resin extraction, the results obtained in our laboratories clearly showed that the published purification procedure does not lead to the isolation of pure methanobactin. Due to this unforeseeable result, an additional laborious purification by HPLC had to be implemented to obtain highly pure methanobactin which is prerequisite for the performance of the planned laboratory studies. The unexpected need for developing and optimizing the HPLC method as well as the characterization of the products required additional time not included in the original project schedule. Therefore, we request to extend the current project by 18 months to be able to complete the Ph.D. thesis of Marie-Laure Pesch. The extension is needed to conduct the planned equilibrium exchange experiments and to study the kinetic aspects of ligand exchange reactions. The results of these ligand exchange experiments are essential to find out how strongly copper complexation by natural organic matter may affect methane oxidation in wetlands. 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.
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