TABLE 1.

Methyl-based methanogenic substrates

Namea	Abbreviation	Formula	Structureb	CH3-Dism.	CH3-Red.	Environmentsc	Genesd
Tetramethylammonium	QMA	(CH3)4N		X		Marine sediment, industrial wastewater	mtqBCe, mtqAe
Trimethylamine	TMA	(CH3)3N		X	X	Marine sediment, hypersaline sediment, gut	mttBC, mtbA
Dimethylamine	DMA	(CH3)2NH		X	X	Marine sediment, hypersaline sediment, gut	mtbBC, mtbA
Monomethylamine	MMA	CH3NH2		X	X	Marine sediment, hypersaline sediment, gut	mtmBC, mtbA
Methanol	MeOH	CH3OH		X	X	Marine sediment, freshwater sediment	mtaBC, mtaA
Glycine betaine	GB	C5H11NO2		X		Marine sediment, hypersaline sediment	mtgBC, mtgA
Dimethyl sulfide	DMS	(CH3)2S		X		Marine sediment, hypersaline sediment	mtsAB, mtpC, mtsDEF
Methanethiol	MT	CH3SH		X		Marine sediment, hypersaline sediment, freshwater sediment	mtsAB, mtpC, mtsF
Methylthiopropanoate	MMPA	C5H10O2S		X		Marine sediment, hypersaline sediment	mtpP, mtsA, mtpA, mtpCAP

^aSubstrate names, abbreviations, formulas, structures, use in methyl dismutation (CH₃-Dism.), use in methyl reduction (CH₃-Red.), environments in which the substrates are present, and genes involved in the demethylation and methyl transfer to coenzyme M are shown.

^bStructure diagrams from ModelSEED.

^cMarine sediments here include ocean sediments as well as coastal and estuarine sediments, which are influenced by seawater.

^dPathway-specific genes. All pathways would additionally need mcrABG. Some pathways would additionally require the Wood-Ljungdahl methyl branch and hydrogenases and membrane-bound proteins (Fig. 2).

^eHypothesized but only demonstrated by one study.