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Size isn't only mystery of huge virus

Strange replication method and unusual genetic sequence among the mysteries

Pandoravirus salinus, the largest virus ever identified, has been found on the seafloor off the coast of Chile.

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The largest virus ever identified has been found on the seafloor off the coast of Chile. Pandoravirus salinus is about twice as long as the previous record holder, Megavirus chilensis, with a genome that is twice as large. That makes P. salinus larger than the smallest bacteria.

Beyond its impressive size, the Pandoravirus is strange in some other ways. Rather than reproducing by first making a viral coat and then filling it in or by building its coat around genetic material, P. salinus builds its insides and outsides simultaneously, starting at one end of the horseshoe-shaped viral particle and finishing at the other. What’s more, only 7 percent of the virus’s genes match any known gene sequences, researchers report in the July 19 Science.

The authors suggest a controversial hypothesis for why the Pandoravirus is so odd: It could have evolved from a type of free-living, ancient cell that no longer exists. Its discovery is likely to add fuel to the heated debate about the evolutionary origins of viruses.

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