Ancient virus genomes preserved in glaciers reveal the history of Earth's climate – and how viruses adapt to climate change

As humans alter our planet's climate and ecosystems, scientists study Earth's history to predict the potential consequences of climate change. To do this, giant ice structures like glaciers serve as nature's freezers, archiving detailed records of past climates and ecosystems – including viruses.

We are a team of microbiologists and paleoclimatologists studying ancient microorganisms, including viruses, preserved in glacial ice. Together with our colleagues Lonnie Thompson, Virginia Rich, and other researchers from the Ice Core Paleoclimatology Group at Ohio State University, we are studying 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 communities to specific climate 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.

Read the story of viral genes

We primarily used metagenomes – genome collections that capture the entire genetic content of all microorganisms present in environmental samples – to reconstruct viral genomes from nine different time intervals within the Guliya ice core. These time horizons span three major cold-warm cycles and provide a unique opportunity to observe how viral communities have changed in response to different climatic conditions.

Through our analyses, we were able to restore the genomes of 1,705 virus species, increasing the number of known ancient viruses preserved in glaciers more than fifty-fold.

Only about a quarter of the virus species we found shared species-level similarities with viruses identified in nearly 1,000 metagenomes previously collected in global datasets. Most of these overlapping species were also from the Tibetan Plateau. This suggests that at least some of the viruses preserved in Guliya Glacier originated from the region, but also speaks to the relative paucity of glacier viruses in available databases.

Using these new reference genomes, we tried to “read” their stories.

One of the key findings was that viral communities differed significantly between cold and warm climate periods. The most distinct community of viral species on the glacier emerged about 11,500 years ago, coinciding with the major transition from the last ice age to the Holocene. This suggests that the unique climate conditions during cold and warm periods strongly influenced the composition of viral communities. We suspect that these influences are likely due to viruses being blown in from other locations by changing wind patterns and being subjected to selection pressure from the changing temperatures on the glacier.

Next, we investigated how viruses interact with their hosts. We used computer models to compare viral genomes with the genomes of other microbes that also exist in that environment. We found that viruses consistently Flavobacteriaa lineage of bacteria commonly found in glacial environments.

We also learned that viruses on Guliya Glacier must “steal” genes from their hosts to manipulate their metabolism. The viral genome encodes 50 auxiliary genes for metabolism, including the synthesis and degradation of vitamins, amino acids, and carbohydrates. Some of these genes were present in high abundance at all nine time intervals studied, suggesting that they help microbial hosts cope with the harsh conditions on glacier surfaces and thus improve viral fitness.

Viruses not only infect and kill cells, but probably also alter the fitness of their hosts during infection, thereby influencing their ability to survive under the extreme conditions of a glacial environment.

Climate change over time

Our findings provide a new perspective on how life in the form of viruses has responded to climate change over tens of thousands of years.

Understanding these ancient interactions provides a unique opportunity for future research in both virology and climate science. By studying the response of ancient viruses to past climate changes, researchers can gain valuable insights into how viruses adapt to ongoing global climate change.

We believe that glacial ice, because it stores information about microorganisms and their ecosystems over time in each layer, will continue to be a critical resource for studying Earth's climate history and the life that sustains it – especially given the rapid decline in glacial ice reserves.