Thermodynamic and kinetic analysis of the H2 threshold for Methanobacterium bryantii M.o.H

Fatih Karadagli, Bruce Rittmann

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


H2 thresholds, concentrations below which H2 consumption by a microbial group stops, have been associated with microbial respiratory processes such as dechlorination, denitrification, sulfate reduction, and methanogenesis. Researchers have proposed that observed H 2 thresholds occur when the available Gibbs free energy is minimal (ΔG ≈ 0) for a specific respiratory reaction. Others suggest that microbial kinetics also may play a role in controlling the thresholds. Here, we comprehensively evaluate H2 thresholds in light of microbial thermodynamic and kinetic principles. We show that a thermodynamic H2 threshold for Methanobacterium bryantii M.o.H. is not controlled by ΔG for methane production from H2 + HCO 3 - . We repeatedly attain a H2 threshold near 0.4 nM, with a range of 0.2-1 nM, and ΔG for methanogenesis from H2 + HCO 3 - is positive, +5 to +7 kJ/mol-H2, at the threshold in most cases. We postulate that the H2 threshold is controlled by a separate reaction other than methane production. The electrons from H 2 oxidation are transferred to an electron sink that is a solid-phase component of the cells. We also show that a kinetic threshold (S min) occurs at a theoretically computed H2 concentration of about 2400 nM at which biomass growth shifts from positive to negative.

Original languageEnglish (US)
Pages (from-to)439-452
Number of pages14
Issue number4
StatePublished - Aug 2007


  • Gibbs free energy
  • Hydrogen
  • Methanobacterium bryantii
  • Microbial kinetics
  • Thresholds

ASJC Scopus subject areas

  • Environmental Engineering
  • Microbiology
  • Bioengineering
  • Environmental Chemistry
  • Pollution


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