Essential anaplerotic role for the energy-converting hydrogenase Eha in hydrogenotrophic methanogenesis

Thomas J. Lie, Kyle C. Costa, Boguslaw Lupa, Suresh Korpole, William B. Whitman, John A. Leigh

Research output: Contribution to journalArticlepeer-review

58 Scopus citations

Abstract

Despite decades of study, electron flow and energy conservation in methanogenic Archaea are still not thoroughly understood. For methanogens without cytochromes, flavin-based electron bifurcation has been proposed as an essential energy-conserving mechanism that couples exergonic and endergonic reactions of methanogenesis. However, an alternative hypothesis posits that the energy-converting hydrogenase Eha provides a chemiosmosis-driven electron input to the endergonic reaction. In vivo evidence for both hypotheses is incomplete. By genetically eliminating all nonessential pathways of H2 metabolism in the model methanogen Methanococcus maripaludis and using formate as an additional electron donor,we isolate electron flow formethanogenesis from flux through Eha. We find that Eha does not function stoichiometrically for methanogenesis, implying that electron bifurcation must operate in vivo. We show that Eha is nevertheless essential, and a substoichiometric requirement for H2 suggests that its role is anaplerotic. Indeed, H2 via Eha stimulates methanogenesis from formate when intermediates are not otherwise replenished. These results fit the model for electron bifurcation, which renders the methanogenic pathway cyclic, and as such requires the replenishment of intermediates. Defining a role for Eha and verifying electron bifurcation provide a complete model of methanogenesis where all necessary electron inputs are accounted for.

Original languageEnglish (US)
Pages (from-to)15473-15478
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number38
DOIs
StatePublished - Sep 18 2012
Externally publishedYes

Keywords

  • Ferredoxin
  • Formate dehydrogenase
  • H:f oxidoreductase
  • Hydrogenotrophs

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