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Ice Viruses
October 21, 1999
Tomato mosaic tobamovirus
ToMV
image: John Castello

Freezing is a well-known means of preservation, but scientists have recently discovered just how effective it can be. A team at the State University of New York has announced in the journal Polar Biology the discovery of the oldest known virus to date, frozen more than a mile beneath the Greenland ice pack. Although what they found is a known virus, the discovery raises the question of whether there are prehistoric viruses never encountered by man buried beneath the ice.

What Did They Find?

Scientists isolated the RNA of tomato mosaic tobamovirus (ToMV), from ice cores obtained at several drilling sites throughout Greenland. The cores have been dated to between 500 and 140,000 years old. "To the best of my knowledge, this is the first time anyone has found a virus in any substance that old, whether it be ice or deep ocean sediments," says John Castello, professor of plant virology at SUNY College of Environmental Science and Forestry and a member of the team that analyzed the cores.

image: Mark Twickler

The ice cores, which took five years to collect, extended 3000 meters—almost two miles—below the earth’s surface, according to Mark Twickler, a glaciologist at the University of New Hampshire and associate director of the Greenland drill site known as GISP2. They are well dated because approximately three feet of snow falls in Greenland each year and the summer and winter snow has a different texture. So scientists can tell the age of a core just by looking at its "rings." They also analyze the cores’ chemical composition to glean clues about its age, Twickler says.

Although bacteria and fungi had already been found in ice, ToMV, a plant pathogen that Castello says is one of the most stable viruses known to mankind, is the first virus to be detected in ice. Castello and his colleagues are now trying to determine if the ToMV they found is still infectious. Their project, which is funded by the National Science Foundation (NSF), will also be looking for other types of viruses in the ice cores, such as those that cause polio, influenza and gastroenteritis. He says that its presence might mean that other plant viruses—or even viruses that infect humans—might also be lurking in ancient ice.

So Should We Worry?

image: NSF

Now that scientists know viruses can be preserved in ice, the next question is whether they can be unleashed if the ice melts. "[A]nything that’s entrapped in this ice is going to be recycled into the modern environment as these glaciers melt and as they erode and as they calve [when floating glacial ice breaks up into icebergs]," says Castello, adding that the process could be accelerated by global warming. But, he says, "the one thing you have to keep in mind is that glaciers are always melting, they’re always calving, they’re always eroding, and they have been for thousands of years." So it’s likely that microorganisms trapped in ice have been continually released into the environment.

But if a pathogen were to be released that mankind had not been exposed to for thousands or hundreds of thousands of years, it’s theoretically possible it could cause an epidemic, since people would not have developed natural immunity, Castello says.

What Next?

Europa - moon of Jupiter
image: NASA

The implications of ToMV being detected in ancient ice may go beyond what happens on earth. "If life can exist in such extreme environments here, not only in ice but in other extreme environments—extremely salty marshes, several miles deep below the surface of the earth in gold mines in Africa—then I think that life has to have evolved in other places not of this earth," says Castello.

Castello thinks scientists searching for life on other planets and moons should start with places where there is lots of ice, like Europa, one of Jupiter’s moons. He hopes the techniques developed by his team and others may one day be used to detect life on extra-terrestrial bodies. The NSF has created a panel called LExEn (for Life in Extreme Environments), which is trying to determine if techniques developed to search for life in harsh environments on earth can be used to search for life elsewhere.

Bringing specimens from other planets back to earth may pose a problem that Castello has already had to face, in part. In order to ensure that the ToMV detected really comes from the ancient ice, his team uses techniques such as ultraviolet radiation on the outside of the cores to kill off any microbes that might be present. They also only take samples from intact cores. Castello emphasized the importance of working under sterile conditions. "If you can1t do that, then you can1t trust the results that you1re generating, so we spend a lot of time running controls and techniques that we feel certain prove what we1re working with is indeed ancient and not modern," he says.

The SUNY team will continue to analyze ice cores from Greenland, as well as older cores from the Antarctic, to find out if there are other kinds organisms preserved there. And according to Castello, although the microbes from the ancient ice have the potential to be dangerous, they are just as likely to be useful to scientists studying modern diseases.

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by STN2


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