Bacterium From Hell

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MOST BACTERIA HAVE THE DECENCY TO BE MICROscopic. Epulopiscium fishelsoni is not among them. The newly identified one-celled macro-microorganism, which lives harmlessly in the intestine of the Red Sea-dwelling brown surgeonfish, is a full fiftieth of an inch long, large enough to be seen with the naked eye. Described in the current Nature, it is a million times as massive as the bacteria that inhabit the human gut.

Epulopiscium is notable for sheer grotesqueness, of course, but it also upsets some long-held scientific assumptions. For one, biologists had believed that bacteria could never be very large because, unlike one-celled animals (such as amoebas), they don't have the internal machinery to spread nutrients through their bodies. Now it appears that some fossilized traces of large microorganisms, which researchers presumed to be from animals, may have come from bacteria instead. If that's true, scientists know less than they thought about the early history of life on earth.