15,000-year-old viruses found in Tibetan glacier ice

Scientists studying glacier ice have found viruses nearly 15,000 years old in two samples of ice taken from the Tibetan Plateau in China. Most of these viruses, which survived because they remained frozen, do not look like any of the viruses listed so far.

The results, published today in the journal Microbiome, could help scientists understand how viruses have evolved over the centuries. For this study, scientists also created a new, ultra-clean method of analyzing microbes and viruses in ice without contaminating it.

“These glaciers formed gradually, and along with the dust and gas, many viruses also settled in this ice,” said Zhi-Ping Zhong, lead author of the study and researcher at Ohio State University Byrd Polar and Climate Research. Center that also focuses on microbiology. “Glaciers in western China are not well studied, and our goal is to use this information to reflect past environments. And viruses are part of those environments.”

The researchers analyzed ice cores taken in 2015 from the Guliya ice cap in western China. Carrots are collected at high altitudes – the summit of Guliya, where this ice comes from, is 22,000 feet above sea level. Ice cores contain layers of ice that build up year after year. year, trapping whatever was in the atmosphere around them when each layer froze. These layers create a sort of timeline, which scientists have used to better understand climate change, microbes, viruses, and gases throughout history.

The researchers determined that the ice was nearly 15,000 years old using a combination of traditional and new techniques to date this ice core.

When they scanned the ice, they found the genetic codes for 33 viruses. Four of these viruses have already been identified by the scientific community. But at least 28 of them are new. About half of them seemed to have survived by the time they were frozen not despite the ice, but because of it.

“These are viruses that would have thrived in extreme environments,” said Matthew Sullivan, study co-author, Ohio State professor of microbiology and director of the Ohio State Center of Microbiome Science. “These viruses have gene signatures that help them infect cells in cold environments – just surreal genetic signatures for how a virus is able to survive in extreme conditions. These aren’t easy signatures to extract, and the method Zhi-Ping developed to decontaminate carrots and study microbes and viruses in ice could help us search for these genetic sequences in other extreme icy environments – Mars, for example, the moon, or closer to at home in the Atacama Desert on Earth. ”

Viruses do not share a common, universal gene, so naming a new virus – and trying to figure out where it fits in the landscape of known viruses – involves several steps. To compare unidentified viruses with known viruses, scientists compare sets of genes. Known virus gene sets are cataloged in scientific databases.

These database comparisons showed that four of the viruses in the Guliya ice cap core had previously been identified and belonged to families of viruses that typically infect bacteria. The researchers found the viruses at much lower concentrations than those found in the oceans or soil.

The researchers’ analysis showed that the viruses likely originated from the soil or plants, and not from animals or humans, based on both the environment and databases of known viruses.

The study of viruses in glaciers is relatively new: only two previous studies have identified viruses in the ice of ancient glaciers. But it is a field of science that is becoming increasingly important as the climate changes, said Lonnie Thompson, lead author of the study, a distinguished university professor of earth sciences at Ohio State and a senior researcher at the Ohio State University. Byrd Center.

“We know very little about viruses and microbes in these extreme environments, and what is actually there,” Thompson said. “Documenting and understanding this is extremely important: How do bacteria and viruses react to climate change? What happens when we go from an ice age to a warm period like the one we are experiencing now? ”