How to Make a Living by Exhaling Methane

Methane produced in the biosphere is derived from twomajor pathways. Conversion of the methyl group of acetate to CH₄ in the aceticlastic pathway accounts for at least two-thirds, and reduction of CO₂ with electrons derived from H₂, formate, or CO accounts for approximately one-third. Although both pathways have terminal steps in common, they diverge considerably in the initial steps and energy conservation mechanisms. Steps and enzymes unique to the CO₂ reduction pathway are confined to methanogens and the domain Archaea. On the other hand, steps and enzymes unique to the aceticlastic pathway are widely distributed in the domain Bacteria, the understanding of which has contributed to a broader understanding of prokaryotic biology.