by As humans change the planet’s climate and ecosystems, scientists are looking to Earth’s history to help predict what climate change might bring. To that end, massive ice structures such as glaciers act as nature’s freezers, archiving detailed records of past climates and ecosystems – including viruses.
We are a team of microbiologists and paleoclimatologists who study ancient microorganisms, including viruses preserved within glacial ice. Together with our colleagues Lonnie Thompson, Virginia Rich and other researchers at the Ice Core Paleoclimatology group at The Ohio State University, we investigate interactions between viruses and their environment archived in ice cores from the Guliya Glacier on the Tibetan Plateau.
By linking the genomes of ancient viral populations to specific climatic conditions preserved in glacial ice, our newly published research provides insights into how these viruses have adapted to Earth’s changing climate over the past 41,000 years.
Reading history in viral genes
We primarily used metagenomes – genome collections that capture the entire genetic material of all microorganisms present in environmental samples – to reconstruct viral genomes from nine distinct time intervals within the Guliya ice core. These time periods span three major cold-to-warm cycles, providing a unique opportunity to see how viral communities have changed in response to different climate conditions.
Through our analyses, we recovered genomes equivalent to 1,705 virus species, increasing more than fifty times the ancient viruses known to have been preserved by glaciers.
Only about a quarter of the viral species we found showed species-level similarity to any of the viruses identified in nearly 1,000 previously captured metagenomes in a global dataset. Most of these overlapping species also came from the Tibetan Plateau. This suggests that at least some viruses preserved in the Guliya Glacier originated locally in the region, but also speaks to the lack of glacial viruses relative to available databases.
Using these new reference genomes, we attempted to “read” their stories.
One key finding was that viral communities differed significantly between cold and warm periods. The most distinctive community of viral species on the glacier appeared around 11,500 years ago, coinciding with the major transition from the Last Glacial Stage to the Holocene. This suggests that the unique climatic conditions during cold and warm periods had a major impact on the composition of the viral communities. We hypothesize that these impacts are likely due to viruses from elsewhere blowing in through changing wind patterns and subject to selection pressures from changing temperatures on the glacier.
Digging deeper, we determined the way viruses interacted with their hosts. To do this, we used computer models to compare viral genomes with the genomes of other microbes also found in this environment. We discovered that viruses are persistently infectious Flavobacteriuma lineage of bacteria commonly found in glacial environments.
We also learned that viruses on the Guliya Glacier must “steal” genes from their host to manipulate their metabolism. Encoded within the viral genomes were 50 auxiliary metabolic genes related to metabolism, including the synthesis and breakdown of vitamins, amino acids and carbohydrates. Some of these genes were abundant over the nine time intervals studied, suggesting that they help microbial hosts cope with the harsh conditions on glacier surfaces and thus improve viral fitness.
Thus, viruses not only infect and kill cells, but likely alter the fitness of their host during infection, affecting their ability to survive in the extreme conditions of glacial environments.
Climate change over time
Our findings provide a new perspective on how life, in the form of viruses, has responded to climate changes over thousands of years.
Understanding these ancient interactions provides a unique opportunity for future research in virology and climate science. By studying how ancient viruses have responded to climate changes in the past, researchers can gain valuable insights into how viruses adapt to ongoing global climate change.
We believe that glacier ice, by capturing information on microorganisms and their ecosystems over time in each layer, remains a critical resource for unraveling the history of Earth’s climate and the life it has supported – especially as glacier ice reserves decrease rapidly.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: Zhi-Ping Zhong, The Ohio State University; Ellen Mosley-Thompson, The Ohio State University; Lonnie Thompson, The Ohio State University; Matthew Sullivan, The Ohio State Universityand Virginia Rich, The Ohio State University
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Zhi-Ping Zhong receives funding support from a Byrd Postdoctoral Fellowship, the Heising-Simons Foundation, the National Science Foundation, the Gordon and Betty Moore Foundation, and the US Department of Energy’s Joint Genome Institute.
Ellen Mosley-Thompson receives funding from the Heising-Simons Foundation
Lonnie Thompson receives funding from the National Science Foundation, the Chinese Academy of Sciences and the Heising-Simons Foundation
Matthew Sullivan receives funding from the Gordon and Betty Moore Foundation and the US Department of Energy.
Virginia Rich receives funding from the Heising-Simons Foundation.
