archaea
/ ar-KEE-uh /
Archaea are single-celled microbes that, at a glance through a microscope, look just like bacteria — same tiny size, no nucleus, often a wall. For a long time scientists assumed they simply were bacteria, especially since many famous ones thrive in extreme places like boiling hot springs, acid pools, and salt flats. But appearances mislead: archaea are their own separate domain of life, as distinct from bacteria as bacteria are from us.
An archaeal cell is prokaryotic — its loop of DNA floats in the cytoplasm with no nucleus — yet its molecular machinery tells a different story. Archaea build their cell membranes from chemically distinct lipids, and the proteins they use to copy DNA and make proteins resemble ours more than they resemble a bacterium's. This is exactly what Carl Woese's 1977 comparison of ribosomal RNA revealed, and it is why archaea earned their own domain. Their cell walls also lack the peptidoglycan that defines bacterial walls, so penicillin does not affect them.
Archaea are not just oddities of harsh environments; we now know they live in oceans, soils, and even your gut, and they run important chemistry — for instance, the methane-making microbes in marshes and cow stomachs are archaea. They are a quiet reminder that the microbial world is far richer and stranger than the two categories 'bacteria' and 'eukaryotes' once suggested.
The microbes that make the methane in a cow's burps, in a swamp's bubbles, and in your own gut are archaea — a whole branch of life doing chemistry no bacterium or animal can.
Methane-making archaea: a distinct domain hiding in swamps, cows, and us.
The old name 'archaebacteria' is misleading: archaea are not bacteria at all, and they are no more 'primitive' than any other living thing.