(Nature) The organism was initially called NLF, for “new life form”. Jean-Michel Claverie and Chantal Abergel, evolutionary biologists at Aix-Marseille University in France, found it in a water sample collected off the coast of Chile, where it seemed to be infecting and killing amoebae. Under a microscope, it appeared as a large, dark spot, about the size of a small bacterial cell.

Later, after the researchers discovered a similar organism in a pond in Australia, they realized that both are viruses — the largest yet found. Each is around 1 micrometre long and 0.5 micrometres across, and their respective genomes top out at 1.9 million and 2.5 million bases — making the viruses larger than many bacteria and even some eukaryotic cells.

But these viruses, described today in Science1, are more than mere record-breakers — they also hint at unknown parts of the tree of life. Just 7% of their genes match those in existing databases.

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