Table 1.

Overview of the reaction equations that could occur in the possible electron transfer mechanisms of bioelectrochemical methane production. Based on reactions described in Van Eerten-jansen et al. 2014 [17]. Additionally, microorganisms described to possibly take part in the electromethanogenesis process are related to each reaction.

Reaction/Process	Type (Place)	References in Figure 3	Microorganism [References]
${\mathrm{HCO}}_3^{-}+{9\mathrm{H}}^{+}+{8\mathrm{e}}^{-}\stackrel{\mathrm{electricity}}{\to }{\mathrm{CH}}_4+{3\mathrm{H}}_2\mathrm{O}$	BEC (C)	[1]	Methanobacterium palustre [8,19]
			Methanococcus maripaludis [48,49,50]
			Methanobacterium-like (IM1) [51,52]
			Methanosaeta spp. [34]
			Methanosaeta concilii [33]
			Methanosarcina barkeri [12,35]
			Methanothermobacter thermautotrophicus [12,53]
			Methanosaeta harundinacea [34]
			Methanothermobacter sp. [54]
			Methanoculleus sp. [54]
			Methanobacterium sp. [14,54,55]
			Methanosarcina mazei [56]
			Methanothermobacter-like [15]
			Methanobacteriaceae [20]
			Methanobacterium petrolearium [33]
			Methanobacterium subterraneum [33]
			Methanothermobacter thermautotrophicus [9]
			Methanosaeta concilii 2 [34]
${2\mathrm{H}}^{+}+{2\mathrm{e}}^{-}\stackrel{\mathrm{electricity}}{\to }{\mathrm{H}}_2$	BEC (C)	[2,3]	Desulfovibrio vulgaris [57,58]
			Geobacter sulfurreducens [12,59,60]
			Pelobacter carbinolicus [35]
			Hydrogenophaga caeni (EMB71) [19]
			Desulfovibrio putealis (B7-43) [19]
			Desulfovibrio paquesii [61]
			Firmicutes [14,62]
			Proteobacteria [62]
			Bacteroidetes [62]
			Actinobacteria [62]
			Rhodococcus sp. [63]
			Sphingobacteriales [55]
			Desulfovibrio spp. [63]
${2\mathrm{HCO}}_3^{-}+{9\mathrm{H}}^{+}+{8\mathrm{e}}^{-}\stackrel{\mathrm{electricity}}{\to }{\mathrm{CH}}_3{\mathrm{COO}}^{-}+{4\mathrm{H}}_2\mathrm{O}$	BEC (C)	[4]	Sporomusa ovata [64]
			Sporomusa sphaeroides [65,66]
			Sporomusa silvacetica [65]
			Clostridium aceticum [65]
			Clostridium ljungdahlii [65]
			Moorella thermoacetica [65]
			Clostridium thermoaceticum [67]
			Acetobacterium spp. [42,55,68,69,70]
${\mathrm{HCO}}_3^{-}+{2\mathrm{H}}^{+}+{2\mathrm{e}}^{-}\stackrel{\mathrm{electricity}}{\to }{\mathrm{HCOO}}^{-}+{\mathrm{H}}_2\mathrm{O}$	BEC (C)	[5]	Moorella thermoacetica [71]
			Clostridium formicoaceticum [71]
${\mathrm{HCO}}_3^{-}+{\mathrm{H}}_2+{\mathrm{H}}^{+}\to {\mathrm{CH}}_4+{3\mathrm{H}}_2\mathrm{O}$	BC (C)	[6]	Methanobacterium sp. [14,43,55,72]
			Methanobacterium palustre [19]
			Methanobacterium aarhusense [19]
			Methanobacterium formicicum [72]
			Methanobrevibacter arboriphilus [44,56]
			Methanocorpusculum parvum [44]
			Methanocorpusculum labreanum [63]
			Methanobrevibacter [45,70,73]
			Methanosarcina sp. [43]
			Methanosarcina mazei [56]
			Methanoculleus sp. [43,74]
			Methanomicrobiales [20]
			Methanobacterium petrolearium [33]
			Methanobacterium subterraneum [33]
			Methanothermobacter thermautotrophicus [9]
			Methanothermobacter sp. [74]
			Methanococcus maripaludis [47]
${2\mathrm{HCO}}_3^{-}+{\mathrm{H}}_2+{\mathrm{H}}^{+}\to {\mathrm{CH}}_3{\mathrm{COO}}^{-}+{4\mathrm{H}}_2\mathrm{O}$	BC (C)	[7]	Acetobacterium woodii [65]
			Sporomusa silvacetica [65]
			Clostridium aceticum [65]
			Clostridium ljungdahlii [65]
			Moorella thermoacetica [65]
			Clostridium sp. [75]
${\mathrm{CH}}_3{\mathrm{COO}}^{-}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{CH}}_4+{\mathrm{HCO}}_3^{-}$	BC (C)	[8]	Methanosaeta sp. [45,73,76]
			Methanosarcina sp. [7,74,77]
			Methanosarcina thermophila [72]
			Methanosaeta harundinacea [34]
			Methanosarcina mazei [38,56]
${\mathrm{HCO}}_3^{-}+{\mathrm{H}}_2\to {\mathrm{HCOO}}^{-}+{\mathrm{H}}_2\mathrm{O}$	BC (C)	[9]	Acetobacterium woodii [78]
			Candida boidinii [78]
${\mathrm{HCOO}}^{-}+{3\mathrm{H}}_2+{\mathrm{H}}^{+}\to {\mathrm{CH}}_4+{2\mathrm{H}}_2\mathrm{O}$	BC (C)	[10]	Methanococcus maripaludis [79]
			Methanomicrobiales [20]
			Methanobacterium formicicum [72]
${\mathrm{CH}}_4+{2\mathrm{O}}_2\to {\mathrm{CO}}_2+{2\mathrm{H}}_2\mathrm{O}$	BC (C)	n.s.	Acidovorax caeni (R-24608) [19]
			Hydrogenophaga caeni (EMB71) [19]
			Methylocystis sp. (SC2) [19]
Unknown 1	-	-	δ-Proteobacteria [14,45]
			Geobacter sp. [54,76,80]
			Pelobacter carbinolicus [35]
			Desulfovibrio spp. [75,81]
			Synergistetes-like [15,72]
			Thermotogae-like [15]
			Methylocystis sp. [14]
Unknown 2	-	-	Methanospirillum hungatei [12]
			Methanoregula boonei [12]
			Methanocopusculum bavaricum [12]
			Thermoplasma sp. [12]
			Methanoculleus bourgensis [72]
Unknown 3	-	-	Methanobacterium sp. (YCM1) [38]
			Methanobacterium bryantii (RiH2) [38]
			Methanosarcina mazei (Tuc01) [38]
			Methanosarcina thermophila [72]
			Methanobacterium arcticum (M2) [75]
			Methanobacterium bryantii (MOH) [75]
${4\mathrm{H}}_2\mathrm{O}\to {2\mathrm{O}}_2+{8\mathrm{H}}^{+}+{8\mathrm{e}}^{-}$	Ch (A)	n.s.

¹ Higher relative abundance correlated with higher CH₄ production in electromethanogenic biocathode; ² Associated with syntrophic associations with methanogens in the biocathode to produce CH₄; ³ Archaea identified in electromethanogenic BES reactor biocathodes; BEC: Bioelectrochemical; BC: Biochemical; Ch: Chemical; C: Cathode; A: Anode; n.s.: Not shown.