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After a recent survey found genetic hints of giant viruses in seawater, Claverie and his team decided to go on the hunt. They teamed up with oceanographers and scooped out sediment samples from the coast of Chile and a freshwater pond in Australia.
They brought back the samples and placed them in a solution filled with antibiotics, to kill any bacteria that might have been along for the ride. Then they exposed the samples to their laboratory amoebas."If they die, we suspect that there's something in there that killed them," says Chantal Abergel, Claverie's co-author and also his wife.
It worked. The infected amoebas spawned lots of Pandoraviruses. When Abergel and Claverie sequenced the genome of the new virus, they were in for a shock. Its genetic code is roughly twice the size of the record-holding Megavirus. And it seems almost completely unlike anything else on the planet. Only 6 percent of its genes resembled the genes other organisms. Claverie says he thinks the Pandoraviruses may come from a different origin – perhaps radically different.
"We believe that those new Pandoraviruses have emerged from a new ancestral cellular type that no longer exists," he says. That life could have even come from another planet, like Mars. "At this point we cannot actually disprove or disregard this type of extreme scenario," he says.
But how did this odd cellular form turn into a virus? Abergel says it may have evolved as a survival strategy as modern cells took over. "On Earth it was winners and it was losers, and the losers could have escaped death by going through parasitism and then infect the winner," she says.