Melting ice in high latitudes and altitudes does not only raise concerns about the climate, but also has an interest in organisms trapped in permafrost, including, in addition to extremely well preserved animals and strange bacteria, unknown viruses dating back to tens of thousands of years ago. Recently, researchers identified several unknown viruses 15,000 years old, lying in the Guliya ice cap on the Tibetan plateau.
Organisms from Earth’s distant past, whether animals, bacteria or viruses, potentially reveal the history of ancient ecosystems, including details of the environments in which they lived. But the melting has also raised concerns, often unjustified, about the return of old pathogenic viruses.
« The melting will not only result in the loss of these ancient and archived microbes and viruses, but will also release them in the environments to come. The researchers write in the new study, led by microbiologist Zhi-Ping Zhong of Ohio State University.
28 previously unknown viruses
Using new metagenomic techniques and new methods to keep ice samples sterilized, researchers are working to better understand what exactly is hidden in these organisms. In the new study, the team was able to identify an archive of dozens of unique 15,000-year-old viruses from the Guliya ice cap of the Tibetan Plateau and better understand their functions. The results were published in the journal Microbiome.
« These glaciers formed gradually, and with the dust and gas, many viruses were also deposited in this ice. Zhong said in a statement. These microbes potentially represent those in the atmosphere at the time of their deposition, the team explains in its paper.
Indeed, previous studies have shown that microbial communities correlated with changes in dust and ion concentrations in the atmosphere, and may also indicate climatic and environmental conditions at the time. In this frozen record of ancient times, 6.7 kilometers above sea level in China, the researchers found that 28 of the 33 viruses they identified had never been seen before.
« These are viruses that would have thrived in extreme environments Says microbiologist Matthew Sullivan of Ohio State University, with ” gene signatures that help them infect cells in cold environments – just surreal genetic signatures indicating how a virus is able to survive in extreme conditions ».
Where do they come from?
By comparing their genetic sequences to a database of known viruses, the team found that the most abundant viruses in the two samples of ice cores were bacteriophages capable of infecting methylobacteria – bacteria important to the cycle of the methane within the ice.
They were most closely related to viruses found in strains of methylobacteria in plant and soil habitats, which is consistent with an earlier report that the main source of dust deposited on the Guliya ice cap is likely from soils.
« These frozen viruses probably originate from the soil or plants and facilitate the acquisition of nutrients for their hosts. », Concluded the research team. While the discovery of ancient viruses seems particularly worrying in the midst of a pandemic, the greatest danger of melting ice lies elsewhere: massive reserves of sequestered methane and carbon are released into the atmosphere … But ice could also contain information on past environmental changes, as well as the evolution of viruses. Valuable information.
« We know very little about viruses and bacteria in these extreme environments, and what really is there. Says researcher Lonnie Thompson, who notes that many important questions remain unanswered. ” 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? ».