Could Giant Viruses Be the Origin of Life on Earth?

The ancestors of modern viruses might have provided the raw material for life as we know it, according to stunning new discoveries.

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At more than 1.5 micrometers long, pithovirus is the largest virus ever discovered.

Chantal Abergel and Jean-Michel Claveriewere used to finding strange viruses.

The married virologists at Aix-Marseille University had made a career of it. But pithovirus, which they discovered in 2013 in a sample of Siberian dirt that had been frozen for more than 30,000 years, was more bizarre than the pair had ever imagined a virus could be.

In the world of microbes, viruses are small—notoriously small. Pithovirus is not. The largest virus ever discovered, pithovirus is more massive than even some bacteria. Most viruses copy themselves by hijacking their host's molecular machinery. But pithovirus is much more independent, possessing some replication machinery of its own.

Pithovirus's relatively large number of genes also differentiated it from other viruses, which are often genetically simple—the smallest have a mere four genes. Pithovirus has around 500 genes, and some are used for complex tasks such as making proteins and repairing and replicating DNA.

"It was so different from what we were taught about viruses," Abergel said. (Also see "Virus-Infecting Virus Fuels Definition of Life Debate.")

The stunning find, first revealed in March, isn't just...

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