Table 1.

The production and consumption of candidate interspecies electron carriers (IECs) in AOM coupled to SR

Candidate-IEC	Potential subconversions in AOM coupled to SR
Acetate	CH4 + HCO−3 → CH3COO− + H2O	∆Gº’IEC production	+31 kJ mol−1 CH4
	CH3COO− + SO2-4 → HS− + 2HCO−3	∆Gº’IEC consumption	−47 kJ mol−1 SO2-4
Formate	CH4 + 3HCO−3 → 4HCO−2 + H+ + H2O	∆Gº’IEC production	+128 kJ mol−1 CH4
	4HCO−2 + SO2−4 + H+ → HS− + 4HCO−3	∆Gº’IEC consumption	−144 kJ mol−1 SO2−4
Methanol	CH4 + 1/3HCO−3 + 1/3H+ + 1/3H2O → 4/3CH3OH	∆Gº’IEC production	+104 kJ mol−1 CH4
	4/3CH3OH + SO2−4 → HS− + 4/3HCO−3 + 1/3H+ + 4/3H2O	∆Gº’IEC consumption	−120 kJ mol−1 SO2−4
Carbon monoxide	CH4 + 3HCO−3 + 3H+ → 4CO + 5H2O	∆Gº’IEC production	+196 kJ mol−1 CH4
	4CO + SO2−4 + 4H2O → HS− + 4HCO−3 + 3H+	∆Gº’IEC consumption	−212 kJ mol−1 SO2-4
Methanethiol	CH4 + 1/3HCO−3 + 5/3H+ + 4/3HS− → 4/3H3CSH + H2O	∆Gº’IEC production	+55 kJ mol−1 CH4
	4/3H3CSH + SO2−4 → 7/3HS− + 4/3HCO−3 + 5/3H+	∆Gº’IEC consumption	−71 kJ mol−1 SO2-4
Hydrogen	CH4 + 3H2O → 4H2 + HCO−3 + H+	∆Gº’IEC production	+136 kJ mol−1 CH4
	4H2 + SO−4 + H+ → HS− + 4H2O	∆Gº’IEC consumption	−152 kJ mol−1 SO2-4

The standard Gibbs free energy changes were obtained from Thauer et al. (1977)