Biochemistry of anaerobic microorganisms

Most important results

Biochemistry, physiology and ecology of anaerobic bacteria and archaea with a focus on the enzymes and coenzymes involved in the energy metabolism of Clostridia, of sulfate-reducing bacteria and archaea, of methanogenic and methanotrophic archaea, and of aerobic methanotrophic bacteria.

The most important theoretical paper, in which the thermodynamic principles of bacterial growth are outlined, is a review on "Energy conservation in chemotrophic anaerobes" (1977) (in collaboration with K. Decker and K. Jungermann, University Freiburg.

The most important experimental findings:

Nickel and nickel enzymes

Discovery of nickel as a transition metal required for growth of methanogenic archaea and acetogenic bacteria (1979). Finding of nickel in carbon monoxide dehydrogenase (1979), in coenzyme F₄₃₀ (1980), and in hydrogenase (1981).

Coenzyme F₄₃₀ and methyl-coenzyme M reductase

Elucidation of the structure, function and biosynthesis of the nickel-porphinoid coenzyme F₄₃₀, which is the prosthetic group of methyl-coenzyme M reductase (1980 - 2014) (in collaboration with Albert Eschenmoser, Bernhard Jaun and Andreas Pfaltz, ETH Zürich).
Demonstration that methyl-coenzyme M reductase alone can catalyze methyl-coenzyme M reduction to methane (1985).
First demonstration that the heterodisulfide of coenzyme M and coenzyme B is - besides methane - the product of methyl-coenzyme M reduction with coenzyme B (1987).
Discovery, that some methanogenic archaea contain two methyl-coenzyme M reductase isoenzymes (1990-1993).
Evidence that F₄₃₀ has to be in the Ni(I) oxidation state for methyl-coenzyme M reductase to be active (1991-1997).
Elucidation of the crystal structure of methyl-coenzyme M reductase up to 1.16 Angstrom resolution. Identification of 5 posttranslational modifications (1995-2000) (in collaboration with U. Ermler, MPI for Biophysics in Frankfurt). A crystal structure of the enzyme from methanotrophic archaea was solved in 2011.
Studies on the catalytic mechanism of methyl-coenzyme M reductase via EPR spectroscopy (1996-2014) (in collaboration with the groups of Bernhard Jaun and Arthur Schweiger, ETH Zürich).
Evidence for "Half-of-the-sites reactivity" of methyl-coenzyme M reductase and proposal of a dual stroke engine catalytic mechanism (2005-2008).
Discovery that archaea, which anaerobically oxidizing methane to CO₂, contain high concentrations of methyl-coenzyme M reductase (2003-2011) (in collaboration with F. Widdel, MPI for Marine Microbiology, Bremen).
Demonstration that methyl-coenzyme M reductase can catalyze the oxidation of methane at specific rates sufficient to account for the observed in vivo rates of anaerobic methane oxidation (2010(in collaboration with Bernhard Jaun, ETH Zürich).

Carbon monoxide dehydrogenase

Discovery that carbon monoxide dehydrogenase synthesis in Clostridium pasteurianum is dependent on nickel (1979).
Discovery that the nickel enzyme carbon monoxide dehydrogenase is involved in CO₂ reduction to acetate in acetogenic bacteria (1978), in autotrophic CO₂ fixation in methanogenic bacteria, in acetate conversion to methane and CO₂ imethanogenic archaea and in acetate oxidation to CO₂ in sulfate-reducing bacteria and archaea (1978 - 1997).

Hydrogenase

First report that a hydrogenase contains nickel and that the nickel is redox active as revealed by EPR spectroscopy (1981/1982) (in collaboration with Simon Albracht, Amsterdam).
First characterization of an "energy converting [NiFe]- hydrogenase" (Ech) (1998).
Discovery of a nickel-free [Fe]-hydrogenase (Hmd) in methanogenic archae and that this enzyme contains a novel iron-guanylyl-pyridinol cofactor (Fe-GP cofactor) whose structure was elucidated (1990-2008) (in collaboration with Christian Griesinger, MPI für Biophysikalische Chemie, Göttingen, Eckhard Bill, MPI für Bioanorganische Chemie in Mülheim/Ruhr, Wolfram Meyer-Klaucke, EMBL-Outstation, Hamburg and Seigo Shima, MPI Marburg).

Methanogenic enzymes

Discovery and characterization of seven novel enzymes in methanogenic archaea: formylmethanofuran dehydrogenase (Fmd or Fwd); methyltetrahydro-methanopterin: coenzyme M methyltransferase (Mtr); heterodisulfide reductase (Hdr); F₄₂₀H₂ oxidase (FprA); formaldehyde activating enzyme (Fae); energy converting[NiFe]-hydrogenase (Ech) and nickel-free hydrogenase (Hmd) ([Fe]-hydrogenase) (1988 -2006).
Discovery that formylmethanofuran dehydrogenase is either a molybdenum (Fmd) or a tungsten (Fwd) enzyme and that the methyltransferase (Mtr) is a corrinoid (cobalt tetrapyrrole) containing membrane protein) (1988-2000).
Elucidation of the crystal structure of 12 enzymes involved in the C1-metabolism of methanogenic archaea and methanotrophic bacteria (1995-2008. The three most important structures are those of methyl-coenzyme M reductase, methanol:coenzyme M methyltransferase and [Fe]-Hydrogenase (Hmd) apoenzyme and holoenzyme (in collaboration with Ulrich Ermler, MPI for Biophysics in Frankfurt).
Demonstration of Si-face sterospecificity with respect to C5 of F420 of five F420-dependent enzymes (1993-2004).
Demonstration that CO₂ rather than HCO₃^- is the substrate or product of formylmethanofuran dehydrogenase (1997), carbon monoxide dehydrogenase (1989), formate dehydrogenase and pyruvate:ferredoxin oxidireductase (1975).

Energy conservation

First unequivocal demonstration that a sulfate reducing bacterium can grow on H₂ and Sulfate as sole energy source (1978).
Demonstration of reversed electron transport in sulfur-reducing bacteria growing on acetate and sulfur (1986) and in sulfate reducing bacteria growing on lactate in the absence of sulfate (1988).
Discovery that growth of methanogenic archaea is dependent on sodium ions (1981) and that the energy conserving methyltetrahydromethanopterin: coenzyme M methyltransferase complex is a sodium ion pump (1992-2000) (in collaboration with Gerhard Gottschalk, Göttingen).
Demonstration that the conversion of CO to CO₂ and H₂ in Methanosarcina is coupled with the built up of a proton motive force (1989).
Demonstration that the cytoplasmic butyryl-CoA dehydrogenase/Electron transfer flavoprotein complex in Clostridia couples the endergonic reduction of ferredoxin with NADH to the exergonic reduction of crotonyl-CoA with NADH via a novel mechanism referred to as flavin-based electron bifurcation (2007) (in collaboration with W. Buckel, University Marburg).
Proposal that in methanogenic archaea without cytochromes the first and last steps in CO₂ reduction with H₂ to methane are coupled via flavin-based electron bifurcation whereas in methanogenic archaea with cytochromes the two steps are coupled chemiosmotically (2008).
Discovery of electron bifurcating transhydrogenase (NfnAB) in Clostridium kluyveri and Moorella thermoacetica, of an electron-bifurcating [FeFe]-hydrogenase in M. thermoacetica, Clostridium autoethanogenum and Ruminococcus albus and of an electron bifurcating formate dehydrogenase in Clostridium acidurici (2010-2014).

Metabolic pathways

Discovery of a novel pathway of autotrophic CO₂ fixation in methanogenic archaea (1977-1983).
Discovery of a novel pathway of acetate oxidation in sulfate reducing bacteria (1983-1990).
Elucidation of the pathways for the oxidation of lactate to 3 CO₂ and of autotrophic CO₂ fixation in Archaeoglobus species (1988-1997).
Demonstration of acetyl-CoA, methyltetrahydromethanopterin and reduced ferredoxin as intermediates in methanogenesis from acetate (1989 -1992).
Discovery that carbonic anhydrase is involved in the anaerobic metabolism of acetate (1989).
Discovery that enzymes and coenzymes, thought to be unique for methanogenic archaea, are also present in aerobic methanotrophic bacteria (1997- 2001) (in collaboration with M. Lidstrom, University of Washington, Seattle, and J. Vorholt, ETH Zürich).
Discovery of tetrahydrofolate and of tetrahydrofolate specific enzymes in Methanosarcina (2004).
Demonstration of a novel pathway of heme biosynthesis in archaea (2006).

Ecology

Discovery that the growth yield of methanogenic archaea on H₂ and CO₂ increases when the H₂ concentration decreases (1980).
Demonstration that sulfate reducing bacteria can out-compete methanogenic archaea because of lower apparent Km for H₂ and acetate (1982).