by Faye Flam
Vast stretches of permafrost are melting as the Earth’s polar regions warm, thawing ancient viruses and bacteria that had remained frozen for tens of thousands of years. Behind the lurid headlines about “zombie viruses,” there’s some fascinating science — and a warning.
Last month, scientists announced they’d taken a sample of tundra from Siberia, extracted a virus that had been frozen for 50,000 years, and showed it was still capable of infecting its normal host — amoebas. It was not only a virus new to scientists but also a member of an intriguing group of giant viruses. These are shaking up scientists’ understanding of how viruses evolved, representing a sort of missing link with other life forms.
So the size and the age of this virus are both scientifically noteworthy — and the fact that it can cause infections after being frozen since the Stone Age should be a little scary. That’s not because this specific virus will adapt itself to infect humans but because it means other viruses that might be more dangerous to us could also be lurking down there.
The virus found in Siberia infects amoebas by mimicking their favorite food — bacteria — said research leader Jean Michele Claverie. It doesn’t infect cells of mammals. He said he isolated this particular virus because it’s unlikely to spur a new pandemic.
His concern, he said, is that something more dangerous could emerge as people dig kilometer-deep holes in thawing permafrost for mining operations. As the Earth warms and permafrost thaws, it not only opens up new areas for oil exploration and mining, but might also open a Pandora’s Box of pathogens.
There’s already enough cause for concern given that we know thawing permafrost is freeing organisms that exhale methane and carbon dioxide, creating a climate feedback loop that will accelerate global warming. Moreover, scientists warned years ago that digging in such areas could release smallpox virus from human bodies buried in the ground.
Exploring this environment, carefully, has its upsides. This latest finding is shaking up the way scientists understand viruses. Scientists are still puzzling over where viruses came from and debating whether they are alive or just inanimate bits of stray genetic code. Understanding how to define life is at the core of scientists’ quest to find life elsewhere in the cosmos and understand how it originated on Earth.
More than a decade ago, Claverie and his colleagues discovered the first giant virus, dubbed mimivirus because it mimicked bacteria or other more complex organisms. He believed this was not a strange outlier but might represent an ignored branch of the tree of life. Since then he’s found more — including megavirus and pandoravirus.
“It has changed the way we look at viruses,” he said. He believes the giant viruses provide evidence that viruses are alive, in part because they have an evolutionary relationship with the rest of the living world. Although they can’t live independently, being a parasite hasn’t disqualified other organisms from being considered alive.
Scientists are still debating how giant viruses evolved — whether they grew from smaller virus ancestors, or shrunk from more complex ancestral life forms. Claverie thinks other, normal-sized viruses could have descended from more complex bugs that downsized after taking up a parasitic lifestyle.
Why go looking for them in the permafrost? Claverie said he was inspired by a group of scientists who succeeded in growing a plant from seed that had been frozen for 30,000 years. He asked the researchers who made that finding if he could study some of their samples, and in 2014 he announced a virus of record-breaking size had emerged from the sample and infected amoebas in his lab.
The virus he just announced is even older, at 50,000 years, which is the limit for measuring age with carbon dating. There’s no known limit for how long viruses can persist in a frozen state.
To revive the viruses, he puts material from the permafrost in contact with live amoebas — which he calls “bait.” If they get infected by a virus, they show symptoms — flawed division, abnormal shapes. “Our team of people detect that … uh-oh, those amoebas are not very well.” The viruses meanwhile make many more copies of themselves for the scientists to study.
Other researchers I contacted said the viruses themselves are fascinating and important, but they would like to see better evidence that they really came from the frozen tundra and didn’t sneak in later. “Amoebas (and their viruses) are ubiquitous in many environments,” wrote Eric Delwart, a microbiologist at the University of California San Francisco, in an email. “Could some giant viruses or infected amoebas simply have drifted or floated onto these samples?”
Researchers are also analyzing samples of permafrost more broadly for DNA, using techniques similar to DNA forensics. “We can recognize the traces of everything that was ever in this environment, including other viruses,” Claverie said.
There’s no way stop Russia from mining what resources emerge from a melting Siberia, but we should all hope the Russians proceed cautiously. Workers and those who live in mining towns should be monitored for signs of infection. And while some global warming is now inevitable, we should all be invested in keeping it to a minimum. Anything that’s been locked in ice for 50,000 years should probably stay there.
