Which archaeon is the most common methane producer in the human gut?

The most common methane-producing archaeon in the human gut is Methanobrevibacter smithii. It is an anaerobic methanogen that lives especially well in oxygen-poor regions such as the colon and rectum.

Methanobrevibacter smithii is a hydrogenotrophic archaeon. It consumes hydrogen and carbon dioxide produced by other microbes during fermentation, converting them into methane and water. The reaction is commonly summarized as 4H₂ + CO₂ → CH₄ + 2H₂O. By removing hydrogen, the archaeon can help other gut microbes continue fermenting complex carbohydrates efficiently.

Despite its importance, M. smithii is not a bacterium. Archaea are a separate major branch of cellular life, and methanogens are distinguished by their ability to produce methane as a metabolic end product. Its name means a species in the genus Methanobrevibacter; the species name is smithii.

This organism is often discussed in relation to digestion, gut ecology, and breath-methane testing. Its presence varies among individuals, but it is widely recognized as the predominant methanogenic archaeon in the human intestinal microbiota. The other options are archaea or microbes associated with different environments, but they are not the usual human-gut methane producer.