Scientists have collected viruses from almost-15,000-year-old ice samples, taken from glaciers on the Tibetan Plateau. Dozens of species were found to be unknown to science, which could provide an intriguing look back at the history of viral evolution.
Glaciers are fantastic at preserving deep history, as they trap particles of dust, traces of gas, microbes, and plant matter from different time periods. Since these layers build up over time, scientists can drill and study ice cores to learn a huge amount about ancient climates, what was in the atmosphere, and what kinds of life existed at various points of history.
In the new study, led by researchers from Ohio State University, ice cores were drilled from the Guliya ice cap on the Tibetan Plateau, which were dated as far back as 14,400 years old. The team then analyzed these cores for what kinds of viruses they contained, and the genetic codes of 33 viruses were identified. Four of these were found to belong to known types of bacteriophage, viruses that prey on bacteria, but at least 28 of them didn’t match any known type.
The team hypothesizes that the viruses probably originated in plants and soil, but they weren’t necessarily thwarted by the cold – in fact, around half of them seemed to be well suited to life on the ice.
“These are viruses that would have thrived in extreme environments,” says Matthew Sullivan, co-author of the study. “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.”
Contamination by modern microbes is a serious problem for this kind of study, so the researchers developed a new method for sterilizing the ice cores. They removed half-centimeter (0.2-in) layers of the outer material with different techniques – first band saw scraping, then an ethanol wash, and finally a sterile water wash. The inner section of the core could then be examined free of contamination.
The team tested this sterilization process on their own artificial ice cores, which were coated in bacteria, viruses and DNA. After they conducted their three-step process, no traces of these mock contaminants were detected in the inner ice cores.
The researchers say that being able to better study ancient microbes can help scientists better understand the history of their evolution, as well as how they handled changing climates in the past – and how well they might in future. The sterilization method could also come in handy for finding traces of viral genetic sequences in samples taken on the Moon or Mars.
The research was published in the journal Microbiome.
Source: Ohio State University
