The two bacteria in question are called Methanothermobacter wolfeii and Methanobacterium formicicum. These are examples of methanogens, which are among the most ancient forms of life on Earth. The name of the genus may sound exotic, but they're so common that species are found in cow guts, termites, and in any bog where vegetation is rotting and bubbling up swamp gas. That’s because methanogens are an anaerobic bacteria that don’t breathe oxygen. In fact, oxygen is lethal to them. Instead, they ingest hydrogen and carbon dioxide and give off methane gas. In other words, they’re the reason cows fart.