Methylotrophy refers to the ability of an organism to use C1-compounds as energy sources. These compounds include methanol, methyl amines, formaldehyde, and formate.  Several other less common substrates may also be used for metabolism, all of which lack carbon-carbon bonds. Examples of methylotrophs include the bacteria Methylomonas and Methylobacter. Methanotrophs are a specific type of methylotroph that are also able to use methane () as a carbon source by oxidizing it sequentially to methanol (), formaldehyde (), formate (), and carbon dioxide  initially using the enzyme methane monooxygenase.  As oxygen is required for this process, all (conventional) methanotrophs are obligate aerobes.  Reducing power in the form of quinones and NADH is produced during these oxidations to produce a proton motive force and therefore ATP generation.  Methylotrophs and methanotrophs are not considered as autotrophic, because they are able to incorporate some of the oxidized methane (or other metabolites) into cellular carbon before it is completely oxidized to  (at the level of formaldehyde), using either the serine pathway (Methylosinus, Methylocystis) or the ribulose monophosphate pathway (Methylococcus), depending on the species of methylotroph.
In addition to aerobic methylotrophy, methane can also be oxidized anaerobically. This occurs by a consortium of sulfate-reducing bacteria and relatives of methanogenic Archaea working syntrophically (see below). Little is currently known about the biochemistry and ecology of this process.
Methanogenesis is the biological production of methane.  It is carried out by methanogens, strictly anaerobic Archaea such as Methanococcus, Methanocaldococcus, Methanobacterium,
Methanothermus, Methanosarcina, Methanosaeta and Methanopyrus.  The biochemistry of methanogenesis is unique in nature in its use of a number of unusual cofactors to sequentially reduce methanogenic substrates to methane, such as coenzyme M and methanofuran.  These cofactors are responsible (among other things) for the establishment of a proton gradient across the outer membrane thereby driving ATP synthesis.  Several types of methanogenesis occur, differing in the starting compounds oxidized.  Some methanogens reduce carbon dioxide () to methane () using electrons (most often) from hydrogen gas ()  chemolithoautotrophically.  These methanogens can often be found in environments containing fermentative organisms.  The tight association of methanogens and fermentative bacteria can be considered to be syntrophic (see below) because the methanogens, which rely on the fermentors for hydrogen, relieve feedback inhibition of the fermentors by the build-up of excess hydrogen that would otherwise inhibit their growth.  This type of syntrophic relationship is specifically known as interspecies hydrogen transfer.  A second group of methanogens use methanol () as a substrate for methanogenesis. These are chemoorganotrophic, but still autotrophic in using  as only carbon source.  The biochemistry of this process is quite different from that of the carbon dioxide-reducing methanogens.  Lastly, a third group of methanogens produce both methane and carbon dioxide from acetate () with the acetate being split between the two carbons. These acetate-cleaving organisms are the only chemoorganoheterotrophic methanogens.  All autotrophic methanogens use a variation of the reductive acetyl-CoA pathway to fix  and obtain cellular carbon.