TABLE 5.

Free energy and steady-state free energy flux for possible microbially mediated reactionsa

Reaction no.Redox reactionProcessΔG (kJ/mol) (43°C, pH 9.0)ΔG (kJ/mol) (54°C, pH 9.0)ΔG (kJ/mol) (61°C, pH 7.8)FEF (kJ/cell-s) (43°C, pH 9.0)FEF (kJ/cell-s) (54°C, pH 9.0)FEF (kJ/cell-s) (61°C, pH 7.8)
14CO + 5H2O → CH4 + 3HCO3 + 3H+Methanogenesis by CO disproportionation−260−257−233−8.6 × 10−14−9.8 × 10−14−1.0 × 10−13
24H2 + H+ + HCO3 → CH4 + 3H2OHydrogenotrophic methanogenesis−70−63−68−6.6 × 10−14−6.9 × 10−14−8.6 × 10−14
33H2 + CO → CH4 + H2OHydrogenotrophic methanogenesis−117−113−109−3.9 × 10−14−4.3 × 10−14−4.9 × 10−14
44H2 + H+ + 2HCO3 → acetate + 4H2OAcetogenesis−48−41−46−3.9 × 10−14−3.8 × 10−14−5.0 × 10−14
54CO + SO42− + 4H2O → 4HCO3 + HS + 3H+Sulfate reduction−297−295−271−2.0 × 10−14−2.3 × 10−14−2.5 × 10−14
6CO + 2H2O → HCO3 + H+ + H2Water-shift reaction−47−48−41−1.6 × 10−14−1.8 × 10−14−1.8 × 10−14
7CO + H2 → 0.5 acetate + 0.5H+Acetogenesis−72−69−64−2.4 × 10−14−4.2 × 10−14−1.2 × 10−14
84H2 + H+ + SO42− → HS + 4H2OSulfate reduction−107−102−107−7.2 × 10−15−7.9 × 10−15−9.7 × 10−15
9Acetate + SO42− → 2HCO3 + HSSulfate reduction−59−61−61−4.0 × 10−15−4.7 × 10−15−5.5 × 10−15
10Propane + 2.5SO42− + 2H+ → 3HCO3 + 2.5H2S + H2OSulfate reduction−150−153−152−4.0 × 10−15−4.8 × 10−15−5.5 × 10−15
11Acetate + H2O → CH4 + HCO3Acetoclastic methanogenesis−22−23−23−3.9 × 10−15−4.6 × 10−15−5.4 × 10−15
12Ethane + 1.75SO42− + 1.5H+ → 2HCO3 + 1.75H2S + H2OSulfate reduction−97−100−99−3.7 × 10−15−4.4 × 10−15−5.1 × 10−15
13CH4 + SO42− → H2O + HCO3− + HSAnaerobic methane oxidation−37−38−38−2.5 × 10−15−3.0 × 10−15−3.5 × 10−15
  • a FEF, free energy flux.