by Gilberto Flores

As most teenage boys can tell you, farts are flammable. But what most can’t tell you is why they are flammable. Farts are flammable primarily because of a group of microorganisms living in your intestines known as Archaea.

Before I spoil the surprise (and possibly your lunch) about how Archaea contribute to the “blue flame” that has sent many of us into hysterics, I want to give a brief history lesson on these unique life forms.

In the late 1970’s, Carl Woese and a small team of molecular biologists at the University of Illinois were painstakingly cataloguing ribosomal RNA gene sequences to determine the genetic relationship among all organisms when they made a startling discovery. What they found was that a group of organisms that produce methane (methanogens) had sequences that were quite different than those of Bacteria (e.g., E.coli, Salmonella spp.) and Eukaryotes (e.g., plants, animals, fungi). Up until that point, all life had been divided into these two groups, so when Woese and colleagues published their findings stating the methanogens belonged to a ‘third form of life’ they were met with wide skepticism. Many scientists believed Woese to be foolish, but one man’s fool is history’s genius. As other forms of evidence, including differences in fat composition and more gene sequences from other organisms began to pile up in support of this ‘third form of life,’ Woese and colleagues were vindicated as the scientific community accepted the Archaea as a third domain of life. Imagine that, an entire domain of life (there are only three that we know of) discovered less than 40 years ago!

Enough history, now back to farts.

Farts are flammable because of the same methanogens Woese and colleagues were working with when they made their discovery. Methanogens, primarily Methanobrevibacter spp., are found in some (but not all) people’s guts where they combine hydrogen (H2) and carbon dioxide (CO2) to produce methane (CH4). As most of you already know, methane is a flammable gas and is the primary component of the natural gas many of us use to heat our homes. This unique metabolism does not produce a great amount of energy and can only be done in environments completely void of oxygen (anaerobic).

Many people mistakenly think that methane is also why farts stink but in reality methane is odorless. The smell of farts is mostly due to variety of other compounds produced not by Archaea, but by the numerous Bacteria living in our guts. So next time you clear the room with a silent but deadly one, feel free to blame your Bacteria but please keep the Archaea out of it.

About the Author

Gilberto Flores is an interdisciplinary scientist who specializes in microbial ecology. He has worked in a variety of systems ranging from terrestrial and marine hot springs, to the human body, and the built environment. He is currently a post-doctoral researcher in the laboratory of Noah Fierer at the University of Colorado, Boulder.