The study of viruses trapped in glaciers is a relatively new field and one that, as the climate changes, is becoming more relevant. “We know very little about microbes that live in extreme environments,” explains Lonnie Thompson, a researcher at Ohio State University and lead author of the work. “Documenting and understanding these questions is very relevant: how do bacteria and viruses respond to climate change? What happens when we go from an ice age to a warm period like the one we are experiencing now?
How did the viruses get to the glacier?
The ice samples were collected in 2015 at the top of Guliya, in western China. “These glaciers formed gradually, and along with the dust and gases, large amounts of viruses were also deposited,” explains Zhi-Ping Zhong, lead author of the study and a researcher at the Byrd Center for Polar and Climate Research at the State University of Ohio. “Glaciers in western China are not well studied and we aim to use this information to reflect past environments. And viruses are part of those environments”.
Ice cores contain layers that accumulate year after year, trapping everything that was in the atmosphere around them at the time each layer froze. This creates a kind of timeline that scientists have used to understand more about climate change, microbes, viruses, and gases throughout history.
The researchers determined that the ice was almost 15,000 years old using a combination of new and traditional techniques to date this ice core.
Endurance in extreme conditions
When they analyzed the ice, they found genetic codes for 33 viruses. Four of those viruses had already been previously identified by the scientific community, but at least 28 of them are new. About half of them seemed to have survived the moment they froze, not despite the ice, but because of it. “They are viruses that would thrive in extreme environments,” explains Matthew Sullivan, co-author of the study. “These viruses have gene signatures that help them infect cells in cold environments. These signatures are not easy to extract, and the method developed by Zhi-Ping to decontaminate the cores and Studying microbes and viruses in ice could help us search for these genetic sequences in other extreme icy environments: Mars, the Moon or, closer to home, in the Atacama Desert ”.
Since viruses do not share a common universal gene, their identification requires a series of steps. The first is to compare sets of genes, which are cataloged in scientific databases. In the case of this work, which has just been published in the journal Microbiome, the comparisons showed that four of the viruses found had already been previously identified, and they would be families of viruses that typically infect bacteria, in addition to being found in concentrations much lower than those found in the oceans or on the ground. For the authors, this work opens a new window for the characterization and study of the functioning of viral communities in these thousand-year-old glacial environments.
Reference: Zhong, ZP., Tian, F., Roux, S. et al. Glacier ice archives nearly 15,000-year-old microbes and phages. Microbiome 9, 160 (2021). https://doi.org/10.1186/s40168-021-01106-w