Table 1.

Key enzymes for methanogenesis from unusual substrates

Organism	Protein	Gene identifier	Protein identifier
Methanomassilicoccus luminyensis H2 + MeOH	HdrD	WYS_RS12230	WP_019178460
	FpoNMLKJJIHDCBA	WYS_RS00365-420	WP_019176172-83
	HdrABC MvhAGD	WYS_RS07030, WYS_RS08335, WYS_RS08340, WYS_RS07015, WYS_RS07020, WYS_RS07025	WP_026068905, WP_019177711, WP_026068956, WP_019177457, WP_026068904, WP_019177459
Methanosphaera stadtmanae H2 + MeOH	EhbA-P, EhbQ	Msp_1457-42, Msp_1436	ABC57827-12, ABC57807
	HdrA1B1C1	Msp_1476, Msp_1013, Msp_1014	ABC57846, ABC57401, ABC57402
	HdrA2B2C2	Msp_0127-25	ABC56545-43
	MvhDGA	Msp_0314-16	ABC56724-26
	FrhADGB	Msp_1302-05	ABC57679-82
Methanimicrococcus blatticola H2 + MeOH	VhtGACD FrhADGB HdrDE	C7391_RS00170-85, C7391_RS03655-70, C7391_RS01355-60	WP_133516533-36, WP_133517202-05, WP_133516741-42
Methanonatronarchaeum thermophilum H2 + MeOH	HdrDE HyaABD FdhABDI Multisubunit hydrogenase	AMET1_RS05590–95, AMET1_RS03000–05, AMET1_RS02990, AMET1_RS00565–70, AMET1_RS01775, AMET1_RS02995, AMET1_RS07305-75	WP_086637509-10, WP_086637000-01, WP_086636998, WP_086636646, WP_086636543, WP_161490715, WP_086636999, WP_143406895, WP_086637820, WP_086637822, WP_161490830, WP_086637824-25, WP_086637860, WP_086637826-32
Methanosarcina acetivorans Methyl sulfides	MtsD	MA_0859	AAM04298
	MtsF	MA_4384	AAM07726
	MtsH	MA_4558	AAM07897
Methylmercaptopropionate	MtpCAP	MA_4164–66	AAM07512–14
Methanomethylovorans hollandica Methyl sulfides	MtsD, MtsF, MtsH, MtpCAP	METHO_RS06035 METHO_RS01750 METHO_RS03770 METHO_RS05605	WP_015324657 WP_015323796 WP_015324192 WP_015324567
Methanosarcina MTP4 Methyl sulfides	MtsD MtsF MtsH MtpCAP	MSMTP_RS14200 MSMTP_RS14235 MSMTP_RS00505 MSMTP_RS03110-20	WP_048180685 WP_048180700 WP_048177073 WP_052718253 WP_048177774 WP_082090704
Methanosarcina semesiae Methyl sulfides	?	?	?
Methermicoccus shengliensis ZC-1 Methoxylated aromatic compounds	MtvB O-demethylase	BP07_RS03255	WP_042685518
	MtvB O-demethylase	BP07_RS03250	WP_042685515
	Corrinoid protein	BP07_RS03260	WP_042685521
	MtrH-like methyltransferase	BP07_RS03240	WP_042685937
	Corrinoid activation protein	BP07_RS03235	WP_042685513
Methanococcoides Tertiary amines	?	?	?
Methanolobus vulcani Quaternary amines	MtgB methyltransferase	FKV42_RS08545	WP_154809802
	Corrinoid protein	FKV42_RS08550	WP_154809803
	Corrinoid activator	FKV42_RS10455	WP_154810143
	CoM methyltransferase	FKV42_RS10480	WP_154810148

For the organisms conducting hydrogen-dependent methylotrophic the enzymes important for energy conversion/recycling of reducing equivalents are shown as those play an important role of the special metabolism of those organisms and they are also depicted in Fig. 4. For the other organisms, we focused on the enzymes mentioned in the text and/or shown in Fig. 5. EhbA-Q: energy-conserving hydrogenase, VhtGACD: [NiFe]-hydrogenase, FpoA-O: F₄₂₀H₂ dehydrogenase, HdrDE: membrane-bound heterodisulfide reductase, HdrABC: soluble heterodisulfide reductase, MvhAGD: F₄₂₀-non-reducing hydrogenase, FrhADGB: coenzyme F₄₂₀-reducing hydrogenase, MtrH: tetrahydromethanopterin S-methyltransferase subunit, MtsDFH: proteins involved in the catabolism of dimethylsulfide, MtpCAP: proteins involved in the catabolism of methylmercaptopropionate (MMPA). MtvB: O-demethylase, MtgB methyltransferase