Unknown viruses discovered in 15,000-year-old icebergs

Unknown viruses discovered in 15,000-year-old icebergs

Most – which survived not despite the ice, but because of the ice – turned out to be different from all viruses cataloged so far.

Scientists who studied glacial ice thousands of years ago made a surprising discovery. In two ice samples drilled on the Tibetan plateau in China, they found viruses unknown until recently. According to the researchers, the findings can help us understand, among other things, how viruses have evolved over the centuries.

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Researchers analyzed ice core samples drilled in 2015 in the Julia Ice Sheet located in western China. The cores were collected at a very high altitude, above the Julia River, which is about 6,700 meters above sea level. Ice cores contain layers of ice that have accumulated year after year. These layers actually store whatever was in the atmosphere at the time the ice froze. “These glaciers formed gradually,” researcher Zhi-Ping Zhong explains. “Besides dust and gases, a lot of viruses were also deposited in this ice.”

Using a combination of traditional and new techniques up to the date of the ice cores, the researchers determined that the ice studied dates back nearly 15,000 years. Then they looked at the ice core. And they found something special in the glacial ice. It has discovered at least 33 viruses, 28 of which are unknown. It is remarkable that most of these viruses survived not despite the ice, but thanks to the ice. Moreover, it turns out to be different from all viruses that have been cataloged so far.

Researchers study an ice core that was dug out of the Julia Ice Sheet on the Tibetan Plateau in 2015. The ice contained viruses that are nearly 15,000 years old. Photo: Loni Thompson, Ohio State University

“These are viruses that circulate in harsh environments,” said study researcher Matthew Sullivan. “They have a genetic signature that helps them infect cells in cold environments. They really are surreal genetic signatures of how the virus survives in extreme conditions.”

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Viruses do not share a common universal gene. So naming a new virus — and trying to figure out where it is in the virus landscape — requires several steps. To compare unknown viruses with known viruses, scientists rely on gene combinations. Gene sets of known viruses are indexed in scientific databases. Four of the viruses found in ice cores have been previously described and come from viral families that naturally infect bacteria. Further analysis reveals that the viruses likely came from soil or plants, not animals or humans.

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Results It may also affect the search for life in other harsh environments. In the study, researchers developed a new method for analyzing microbes and viruses in ice. “This method can help us search for genetic sequences in other extreme environments,” Sullivan suggests. “Think of the Moon and Mars, for example. But also closer to home, as in the Atacama Desert on Earth.”

The study of viruses in glaciers is relatively new. So far, only two other studies have found viruses in ancient glacial ice. However, researcher Loni Thompson sees it as a scientific field growing in importance with climate change. “We know very little about viruses and microbes in extreme environments,” he says. However, documenting and understanding it is extremely important. For example, how do bacteria and viruses respond to climate change? And what happens if we go from an ice age to a warm period, like now? The researchers hope to answer these questions in future studies.

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