Discovery of the mightiest baffles biology bacterium: Fish bug can be seen with naked eye

THE LARGEST bug on Earth - a bacterium just visible to the naked eye - has set up home in the gut of a fish that lives off the west coast of Australia.

At more than half a millimetre long, the mighty microbe is a million times as big in volume as its nearest rival, a harmless bacterium that thrives in the murky world of the human colon.

The size of the micro-organism is baffling scientists, who say it should be impossible for such a primitive cell to survive. The volume of the bug is apparently too large, and its surface area too small, to allow nutrients to diffuse into it. Because bacteria belong to a primitive branch of life, with simple cells lacking internal structure, scientists thought they could never grow much bigger than those living in the human gut. The discovery, reported in today's issue of the science journal Nature, has forced researchers to rethink their theoretical assumptions.

Epulopiscium fishelsoni - the bacterium that is as awesome as its name - lives in the intestinal tract of the surgeonfish and was previously confused with a higher form of life, such as an alga or an amoeba. However, when the biologists Esther Angert and Norman Pace, from Indiana University, and Kendall Clements, from James Cook University in Australia, analysed its genetic material they found it was a bacterium that evolved billions of years ago.