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, 80 (4), 1539-41

Thermodynamic Constraints on Syntrophic Acetate Oxidation

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Thermodynamic Constraints on Syntrophic Acetate Oxidation

Jan Dolfing. Appl Environ Microbiol.

Figures

FIG 1
FIG 1
Thermodynamic constraints on syntrophic processes involved in hydrocarbon degradation under sulfate-reducing and methanogenic conditions at 22°C under standard conditions (solutes at 1 M, gases at 1 atm, unless otherwise indicated), with hexadecane as the model hydrocarbon and hydrogen (A) or formate (B) as the interspecies electron carrier. (A) Acetate oxidation is exergonic to the right of the dotted line; hydrogenotrophic methanogenesis is exergonic at hydrogen partial pressure (PH2) > 10−5.84 atm (open circles); hydrogenotrophic sulfate reduction is exergonic at PH2 >10−6.73 atm (closed circles). (B) Acetate oxidation is exergonic to the right of the dotted line; formate-driven methanogenesis is exergonic at [formate] > 10−5.65 M (open circles); formate-driven sulfate reduction is exergonic at [formate] > 10−6.54 M (closed circles); calculations after Dolfing et al. (17).
FIG 2
FIG 2
Effects of pH and pE on the energetics of DIET-mediated methanogenic acetate oxidation. (A) The window of opportunity in which acetate oxidation and methanogenesis are both exergonic under otherwise standard conditions is between pH 1.8 and pH 2.8. Closed symbols, CH3COO + 2H2O → 2CO2 + 7H+ + 8eG0 = 10.3 kJ/mol electrons); open symbols, CO2 + 8H+ + 8e → CH4 + 2H2O (ΔG0 = −16.3 kJ/mol electrons). (B) Electron activity diagram. At pE = 0, the window of opportunity is between pH 1.8 and pH 2.8, and at pH 7, the window of opportunity is between pE = −4.1 and pE = −4.9; the latter values translate into electron potentials of 244 mV and 290 mV, respectively. The standard conditions used were gases at 1 atm, solutes at 1 M, temperature of 25°C, pH = pE = 0; calculations after Dolfing et al. (17, 18) and Hanselmann (19).

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