Comparative analysis of aceticlastic methanogenesis in Methanosarcina and Methanosaeta species

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The major part of methane production on earth originates from the methyl group of acetate, but only the genera Methanosarcina (Ms.) and Methanosaeta (Mt.) are able to use acetate for methanogenesis and growth. Members of these genera are also of great importance for the productivity of biogas plants. The membrane-bound electron transport system and the energy conserving mechanism of Methanosaeta sp. are largely unknown. Even with the knowledge from the genome sequence of Mt. thermophila it cannot be explained how the utilization of acetate leads to a net synthesis of ATP. The overall goal of this project will be the comparison of acetate utilization in Ms. mazei and Mt. thermophila. The topics include the mechanism of acetate uptake and the function of the acetyl-CoA synthetases. Also of central importance is the pyrophosphatase from Mt. thermophila, which will be analysed with respect to possible regulatory effect of adenine nucleotides. In addition, we will analyze whether pyrophosphate, which is produced in the course of acetate activation, is used for energy conservation in Mt. thermophila. This organism only contains gene for the production of the F420H2 dehydrogenase and the heterodisulfide reductase. All other energy conserving oxidoreductases found in Methanosarcina species are obviously missing. It is also unclear how electrons from reduced ferredoxin are transferred into the respiratory chain for heterodisulfide reduction. To shed light on these issues we would like to analyze the electron transport chain of this organism in detail.