Novel reactions involved in energy conservation by methanogenic archaea

Abstract

Methanogenic archaea of the order Methanosarcinales which utilize C(1) compounds such as methanol, methylamines or H(2)+CO(2), employ two novel membrane-bound electron transport systems generating an electrochemical proton gradient: the H(2):heterodisulfide oxidoreductase and the F(420)H(2):heterodisulfide oxidoreductase. The systems are composed of the heterodisulfide reductase and either a membrane-bound hydrogenase or a F(420)H(2) dehydrogenase which is functionally homologous to the proton-translocating NADH dehydrogenase. Cytochromes and the novel electron carrier methanophenazine are also involved. In addition, the methyl-H(4)MPT:HS-CoM methyltransferase is bioenergetically relevant. The enzyme couples methyl group transfer with the translocation of sodium ions and seems to be present in all methanogens. The proton-translocating systems with the participation of cytochromes and methanophenazine have been found so far only in the Methanosarcinales.

Methanogenic potential and microbial community of anaerobic batch reactors at different ethylamine/sulfate ratios

“…With respect to the Bacteria domain, methylotrophic ability is especially widespread within the Proteobacteria phylum, encompassing the alpha, beta and gamma subdivisions (Hanson andHanson, 1996, Kalyuzhnaya et al, 2006). Within the methanogenic archaea, the order Methanosarcinales contains species with the most versatile substrate spectrum, including microorganisms that are able to grow on methylotrophic substrates such as methanol or methylamines as their sole carbon and energy sources (Deppenmeier et al, 1999).…”

Loss of the mtr operon in Methanosarcina blocks growth on methanol, but not methanogenesis, and reveals an unknown methanogenic pathway

“…The carbonyl group is then oxidized to carbon dioxide, whereas the methyl moiety is transferred to tetrahydrosarcinapterin (H 4 SPT) and subsequently reduced to methane (6) . Finally, the methylotrophic pathway involves the disproportionation of C-1 compounds, such as methanol and methylamines, to carbon dioxide and methane (8). One molecule of substrate must be oxidized to produce the reducing equivalents needed to reduce three molecules to methane (8).…”

“…Finally, the methylotrophic pathway involves the disproportionation of C-1 compounds, such as methanol and methylamines, to carbon dioxide and methane (8). One molecule of substrate must be oxidized to produce the reducing equivalents needed to reduce three molecules to methane (8).…”

Molecular Biology of Microbial Hydrogenases

“…In Methanosarcina mazei, the energy-conserving electron transfer from H 2 involves a [NiFe]-H 2 ase, a b-type cytochrome and F 420 H 2 dehydrogenase. The F 420 H 2 dehydrogenase, encoded by the fpo genes, is a redox-driven proton pump sharing similarities with the proton-translocating NADH:quinone oxidoreductase of respiratory chains (Bäumer et al, 2000; reviewed by Deppenmeier et al, 1999).…”