Comparative analysis of aceticlastic methanogenesis in Methanosarcina and Methanosaeta species
Zusammenfassung der Projektergebnisse
Methane-forming archaea are strictly anaerobic microbes and are essential for global carbon fluxes since they perform the terminal step in breakdown of organic matter in the absence of oxygen. The major part of methane produced in nature derives from the methyl group of acetate. Only members of the genera Methanosarcina (Ms.) and Methanosaeta (Mt.) are able to use this substrate for methane formation and growth. Since the free energy change coupled to methanogenesis from acetate is only −36 kJ/mol CH4, aceticlastic methanogens developed efficient energy-conserving systems to handle this thermodynamic limitation. It was already shown that aceticlastic methanogens perform anaerobic respiration to establish an electrochemical ion gradient that is used for ATP synthesis. Key compounds are reduced ferredoxin (Fdred) and the heterodisulfide (CoM-S-S-CoB) formed in the course of aceticlastic methanogenesis. Fdred functions as electron donor and CoM-S-S-CoB is used as electron acceptor by the respiratory chain. CoM-S-S-CoB is reduced by a membrane bound heterodisulfide reductase (Hdr) in Methanosarcina and Methanosaeta spp. However, it was unclear how electrons from Fdred are channelled into the respiratory chain. We could show that in Ms. mazei the Ech hydrogenase performs this function and produces H2 and translocates 1 H+ across the membrane. The H2-uptake hydrogenase (Vho) finally reduces methanophenazine, the electron donor of the heterodisulfide reductase. In contrast, in Ms. acetivorans the Rnf complex is involved in Fdred oxidation. Our data are consistent with the hypothesis that the Rnf complex of Ms. acetivorans is Na+-motive and the entry point of electrons derived from ferredoxin into the electron transport chain. Mt. species do not contain Ech or Rnf instead the organisms possess a truncated form of the F420H2 dehydrogenase (Fpo complex) without the electron input module FpoF. This protein was therefore a candidate for electron input into the respiratory chain. For the investigation of the electron transport system in Mt. thermophila, Ms. mazei ferredoxin MM1619 was reduced with the thermophilic Moorella thermoacetica CODH/ACS and incubated with Mt. thermophila membranes. We observed that heterodisulfide reduction was strictly dependent on ferredoxin and proceeded with a velocity of 470 mU mg-1 membrane protein indicating the presence of a Fd: heterodisulfide oxidoreductase composed of the head-less Fpo complex and the Hdr. Mt. thermophila uses acetate as sole substrate for methanogenesis. We could show that the organism contains a typical AMP-producing acetyl-CoA synthetase that converts acetate into acetyl-CoA for further degradation in the aceticlastic pathway of methanogenesis. Hence, the acetate activation reaction in Mt. thermophila requires the hydrolysis of 2 ATP whereas the acetate activation reaction in Methanosarcina spp. is known to require only 1 ATP. We propose that Mt. thermophila compensates this loss of energy by a more effective H+ translocation in the course of the reaction of the head-less and Fdred dependent Fpo complex in comparison to the reduced F420 dependent Fpo complex in Methanosarcina spp. Acetate uptake was investigated using a Ms. mazei deletion mutant missing the potential acetate transporter protein MM0903. Our results show that an acetate transporter is involved in aceticlastic methanogenesis and may be an important.
Projektbezogene Publikationen (Auswahl)
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(2011) Membrane-bound electron transport in Methanosaeta thermophila. J. Bacteriol. 193: 2868-2870
Welte C, Deppenmeier U
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(2012) A novel inducible protein production system and neomycin as selection marker for Methanosarcina mazei. Archaea vol. 2012, Article ID 973743
Mondorf M, Deppenmeier U, Welte C
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(2012) Acetate activation in Methanosaeta thermophila: characterization of the key enzymes pyrophosphatase and acetyl-CoA synthetase. Archaea Vol. 2012:315153
Berger S, Welte C, Deppenmeier U
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(2012) Electron transport during aceticlastic methanogenesis by Methanosarcina acetivorans involves a sodiumtranslocating Rnf complex. FEBS J. 279: 4444-4452
Schlegel K, Welte C, Deppenmeier U, Müller V
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(2012) Single acquisition of >1000 eubacterial genes: transformtion ofed a methanogen into a facultatively anaerobic heterotroph at the origin of Halobacteria. Proc Natl Acad Sci USA. 109:20537-20542
Nelson-Sathi1 S, Dagan1 T, Landan1 G, Janssen A, Steel M, McInerney J, Deppenmeier U, Martin WF
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(2014) Bioenergetics and anaerobic respiratory chains of aceticlastic methanogens. Biochim Biophys Acta. 1837: 1130-1147. Epub 2013 Dec 12
Welte C, Deppenmeier U
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(2014) Experimental evidence of an acetate transporter protein and characterization of acetate activation in aceticlastic methanogenesis of Methanosarcina mazei. FEMS Microbiol Lett. 359: 147-153
Welte C, Kröninger L, Deppenmeier U
