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