Ice is melting as the world heats up, and sometimes it gives up things we would really rather it didn't. A study of ice from a Tibetan glacier that is nearly 15,000 years old indicates that it could include a lot of viruses we've never seen before. The viruses found so far probably can't infect humans, let alone threaten our health, but we don't yet know what else is lurking there.
"These glaciers were formed gradually, and along with dust and gases, many, many viruses were also deposited in that ice," said Dr Zhi-Ping Zhong of Ohio State University in a statement. "The glaciers in western China are not well-studied, and our goal is to use this information to reflect past environments. And viruses are a part of those environments."
Zhong and co-authors have helped address this with a paper in the journal Microbiome, analyzing ice cores collected near the Guliya summit 6,700 meters (22,000 feet) above sea level. The authors report finding the genetic codes of 33 viruses – only four of which were previously known. These four are phages, viruses that infect bacteria, and are more likely to be put to use by humans than to pose a threat.
Naturally, we know less about the other 29 virus types, but it is thought these also live (if a virus can be said to be alive) in soil microbes or plants, not animals. Many of their suspected hosts, particularly Methylobacterium, were also found trapped in the ice.
"These are viruses that would have thrived in extreme environments," said co-author Professor Matthew Sullivan. "These viruses have signatures of genes that help them infect cells in cold environments – just surreal genetic signatures for how a virus is able to survive in extreme conditions. These are not easy signatures to pull out, and the method that Zhi-Ping developed to decontaminate the cores and to 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 home in Earth's Atacama Desert."
Finding viruses on the Moon would be a shock to science, to say the least, but astrobiologists would love to apply these techniques to some outer Solar System moons.
Microbes were first found in glacial ice more than a century ago, the paper notes. However, it is only as scientists have got used to the idea of a world where ice melt is accelerating that the topic has been much studied. Viruses have been reported in glacial ice only twice before, but this may reflect a failure to look, or the fact that most ice cores come from Antarctica and Greenland, far from likely sources.
We think of viruses – particularly lately – as doing nothing but harm to their hosts. However, some are actually beneficial, and Zhong and Sullivan think that was likely the case for most of those found. These viruses may help bacteria survive in the extreme environments close to the glacier, for example by transferring genes that help their hosts acquire nutrients.