Piezo-tolerant natural gas-producing microbes under accumulating pCO2

Table 2 Gibbs free energy change of relevant reactions and CO₂ speciation (based on \( \Delta G_{\text{f}}^{0} \) [32])

Eq nr	Reaction equation substrates	Products	\( \Delta G_{\text{r}}^{{0,{\text{a}}}} \) (kJ reaction⁻¹)	\( \Delta G_{\text{r}}^{\text{b}} \) (kJ reaction⁻¹)	\( \Delta G_{\text{r}}^{\text{c}} \) (kJ reaction⁻¹)	\( \Delta G_{\text{r}}^{\text{d}} \) (kJ reaction⁻¹)
1*	Acetate⁻ + H₂O	CH₄ + HCO₃ ⁻	−31.0	−25.8	−19.2	−17.5
2a**	4H₂ + CO₂ (g)	CH₄ + 2H₂O	−130.7	−12.5	−12.9	−53.5
2b**	4H₂ + CO₂(aq)	CH₄ + 2H₂O	−139.1	−12.7	−13.1	−53.7
2c**	4H₂ + HCO₃ ⁻ + H⁺	CH₄ + 3H₂O	−135.5	−21.0	−14.5	−55.0
3a	4H₂ + 2CO₂ (g)	Acetate⁻ + H⁺ + 2H₂O	−95.0	+17.3	+3.4	−37.2
3b	4H₂ + 2CO₂ (aq)	Acetate⁻ + H⁺ + 2H₂O	−111.7	+21.4	+7.5	−33.1
3c	4H₂ + 2HCO₃ ⁻ + 2H⁺	Acetate⁻ + H⁺ + 4H₂O	−104.5	+4.7	+4.7	−35.8
4a	Propionate⁻ + 2H₂O	Acetate⁻ + 3H₂ + CO₂(g)	+71.8	−19.1	−12.1	+18.3
4b	Propionate⁻ + 2H₂O	Acetate⁻ + 3H₂ + CO₂(aq)	+80.1	−18.9	−11.9	+18.5
4c	Propionate⁻ + 3H₂O	Acetate⁻ + 3H₂ + HCO₃ ⁻ + H⁺	+76.5	−10.5	−10.5	+19.9
5a	C₆H₁₂O₆ + 2H₂O	2 acetate⁻ + 2H⁺ + 4H₂ + 2CO₂(g)	−215.9	−342.0	−328.0	−287.4
5b	C₆H₁₂O₆ + 2H₂O	2 acetate⁻ + 2H⁺ + 4H₂ + 2CO₂(aq)	−199.2	−341.6	−327.6	−287.0
5c	C₆H₁₂O₆ + 4H₂O	2 acetate⁻ + 4H⁺ + 4H₂ + 2HCO₃ ⁻	−206.5	−324.9	−324.9	−284.3

ΔG ^0,a_r at 25 °C, pH 7 and 0.10 MPa pressure and 1 M of all aquatic species; \( \Delta G_{\text{r}}^{\text{b}} \) at 30 ^°C 0.01 M aquatic species, 0.15 M HCO₃ ⁻, pH 6.2 and a pCO₂ = 30 kPa and pH₂ = 1 Pa; ΔG ^c_r at 30 °C 0.01 M aquatic species, 0.15 M HCO₃ ⁻, pH pK _a = 6.2 and a pCO₂ = 0.50 MPa and pH₂ = 1 Pa; \( \Delta G_{\text{r}}^{\text{d}} \) at 30 °C 0.01 M aquatic species, 0.15 M HCO₃ ⁻, pH = pK _a = 6.2 and a pCO₂ = 0.50 MPa and pH₂ = 60 Pa; * pCH₄ in ΔG ^0′a_r , ΔG ^b_r , ΔG ^c_r and \( \Delta G_{\text{r}}^{\text{d}} \) is 0.10, 0.07, 1.00 and 2.00 MPa, respectively, ** pCH₄ in ΔG ^0,a_r , ΔG ^b_r , ΔG ^c_r and ΔG ^d_r is 0.10, 0.07, 1.00 and 1.00 MPa, respectively

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