More than 1,700 ancient viruses found in glaciers. Are they a threat to humans?

Produced by: Science Popularization China

Author: Denovo Team

Producer: China Science Expo

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There was a plot in the movie where the protagonist looked for seemingly absurd investment projects in order to spend money. One of them was to transport icebergs from the Arctic to the Alxa Desert in Inner Mongolia Autonomous Region.

This project of "transporting icebergs to the desert" is unlikely to be realized from a practical point of view. The icebergs need to go through an extremely complicated transportation process from the Arctic to the Alxa Desert. Factors such as climate, temperature, and transportation costs will make it unfeasible.

Although no one would actually move the Arctic glaciers to the Alxa Desert, glaciers have enormous research value. Scientists often drill ice cores from glaciers all over the country and transport them to laboratories for research.

For example, scientists at Ohio State University in the United States discovered more than 1,700 ancient viruses in ice core samples retrieved from glaciers on my country's Qinghai-Tibet Plateau.

How to get and transport ice from the Himalayas?

As the "Third Pole", the Qinghai-Tibet Plateau's glaciers not only record climate changes over tens of thousands of years, but also contain rich information on microbial and viral communities, and have extremely high scientific research value.

In recent years, China has launched the Second Comprehensive Scientific Survey and Research on the Qinghai-Tibet Plateau (Second Qinghai-Tibet Scientific Expedition), in which glacier research is one of the important tasks. Through drilling and analysis of glaciers, the scientific expedition team has conducted in-depth research on changes in the glacier environment, microbial diversity, and the response of glaciers to climate change, providing valuable scientific data for global climate research and ecosystem protection.

The process of scientists obtaining ice in the Himalayas is very complicated, and usually requires traveling to remote and high-altitude glaciers. The sampling site is located on the plateau of the Guria Glacier in western China, at an altitude of 6,200 meters. The scientific research team uses special drilling equipment to drill deep into the glacier. The ice core drilled is 309.7 meters deep and about 10 centimeters in diameter. The ice core penetrates to the bedrock of the glacier.

During the drilling, the surface temperature of the glacier could reach minus 21.2°C, the core temperature at a depth of 10 meters was minus 11.6°C, and minus 2.1°C at the bottom of the glacier. The ice core was drilled to a depth of 309.7 meters, which can preserve climate data for tens of thousands of years. Due to the extremely harsh environment at high altitudes, scientists have to face low temperatures, low oxygen and rugged terrain conditions.

The drilled ice cores are divided into sections of about 1 meter in length, sealed in plastic tubes, and then packed into aluminum-covered cardboard tubes. After that, transporting the extracted ice cores down the mountain is a difficult task, because vehicles are usually not available in these glacial areas . Therefore, scientists can only rely on yaks to carry ice cores. Generally, each yak can carry about ten meters of ice core slices. These yaks can not only adapt to the harsh climate and terrain of the mountains, but also help scientists transport ice cores from high-altitude collection sites to lower altitudes.

Glacier ice core sampling

(Image source: Document 1)

Once the ice cores are transported to lower altitudes, scientists will package them properly to ensure that they remain frozen throughout the transportation process. Afterwards, the ice cores will be loaded into refrigerated trucks and transported to scientific research laboratories. Through these ice cores, scientists can gain a deeper understanding of the evolution of ancient climate and microbial ecosystems, thereby revealing the impact of climate change on microbial communities.

What is the significance of studying these ancient viruses?

Glaciers are natural archives of time information and ancient climate and ecosystems on Earth. The ice cores in the Guria Glacier cover more than 41,000 years of historical records, preserving climate and microbial information from different time periods. This study aims to reveal the dynamics of these viral communities with changes in cold and warm climates, as well as their role in ancient ecosystems.

The research team successfully reconstructed 1,705 viruses at the species level by extracting viral genomes from ice cores of the Gulia Glacier on the Tibetan Plateau. These genomes came from samples from nine different periods, spanning three cold and warm climate cycles over the past 40,000 years.

In glacial environments, due to extreme cold and lack of nutrients, the number of microorganisms is usually very low, resulting in a small amount of extracted DNA, which poses a challenge to genome assembly. Compared with the previous study that only recovered 33 viral genomes, this study greatly increased the number of viral genomes through deeper sequencing and optimized low-biomass glacial metagenome assembly methods, providing a large amount of new data for the study of viruses preserved in glaciers.

Distribution of Guria Glacier Virus in Different Environments Around the World

(Image source: Document 1)

In order to conduct in-depth analysis of these newly discovered viruses, the research team applied a classification method based on a gene sharing network and combined it with reference viral genomes in public databases to establish a classification system for viral operational classification units and viral communities.

Using this approach, they discovered specific viral genera (such as Phikmvvirus and Rauchvirus) and revealed the possible ecological roles of these viruses in glacially preserved environments and their interactions with host microbes. These findings greatly expand our understanding of the diversity and ecological functions of glacial viruses.

Viruses play key role in glacial ecosystems

The ecological impact of glacial viruses on host microorganisms reveals the key role of viruses in glacial ecosystems. The study showed that viruses in Gulia Glacier exerted continuous viral infection pressure on host microorganisms (mainly Flavobacterium, Psychrobacter and Polarmonas), which are usually the dominant populations in glacial environments. By analyzing the connection between viruses and hosts, the study found that Flavobacterium was subject to the highest viral pressure throughout the study period, which means that these viruses may have had an important impact on the structure and function of glacial ecosystems over a long period of time.

In addition to host infection pressure, the study also revealed the profound impact of the virus on host metabolism through auxiliary metabolic genes (AMGs). A variety of AMGs related to host metabolism were found in the viral genome, especially in the cofactor and vitamin metabolic pathways.

The study speculates that these genes may help the host adapt to extreme environments, such as the cold and low-nutrient conditions on the surface of glaciers, thereby improving the host's ability to survive and also improving the adaptability of the virus. Through these metabolic genes, the virus may play the role of "ecological regulator" in the glacial ecosystem, affecting the growth, metabolism and environmental adaptability of microorganisms.

These results indicate that glacial viruses not only exert pressure on host microbes through infection, but also affect the host's adaptability in extreme environments through metabolic regulation, which further reveals the important ecological role of viruses in ancient ecosystems.

Are ancient viruses a threat to humans?

Of the 1,705 reconstructed viral genomes, 97% could not be classified into known viral genera, indicating that these glacially preserved viruses are highly novel. These new viruses mainly belong to the class Caudoviricetes, but only 12 viral genera were clearly classified in this study, including Carjivirus, Nickievirus, Myxoctovirus, etc. The remaining viruses lack similarity to known viral genomes, demonstrating that there may be a large number of undiscovered and unstudied viral groups in glacial environments.

Current research is cautious about whether ancient viruses released from glaciers pose a threat to humans. First, ancient viruses have been preserved in glaciers for tens of thousands of years or even longer, usually isolated from modern organisms, so they may have lost the ability to infect modern hosts. These viruses are dormant in extremely cold and oxygen-free environments, and may have undergone long-term genetic drift and evolution, with significant differences from modern viruses or microbial hosts, and therefore may not be able to effectively infect or reproduce in modern humans or animals.

Melting glaciers

(Photo source: veer photo gallery)

However, as climate change intensifies and glaciers melt, these ancient viruses are likely to be re-exposed to the external environment and enter media such as air, water or soil. Although most glacial viruses are bacteriophages that infect bacteria and other microorganisms, given the diversity of ancient viral communities and our limited understanding of their biological characteristics, it cannot be completely ruled out that some viruses have the potential to infect modern hosts , especially in individuals with low immunity or insufficient environmental adaptation. These re-exposed viruses may have an impact on certain microbial communities, which in turn indirectly affects human health or ecosystems.

At present, although there is no direct evidence that these ancient viruses pose a direct threat to the human body, the scientific community believes that as the melting of glaciers brings more exposure to unknown viruses, it is necessary to remain highly vigilant and conduct further research to monitor and assess the potential risks of these viruses. In response to possible environmental and health risks in the future, scientists call for the need to develop more stringent monitoring measures to understand the characteristics of these viruses and their potential impact in the context of climate change.

Conclusion

The current study provides a new perspective for our understanding of climate change in Earth's history through the analysis of viruses preserved in glaciers. Glacial viruses record climate and ecosystem changes over tens of thousands of years, which is important for distinguishing between natural climate change and the impact of human activities on the climate. In addition, these viruses may have played a key role in ancient ecosystems, especially in regulating the metabolism of host microorganisms in extreme environments. We look forward to more research in the future to further uncover the secrets frozen in temperature and time in glaciers.

References:

1.Zhong, Zhi-Ping, et al. "Glacier-preserved Tibetan Plateau viral community probably linked to warm–cold climate variations." Nature Geoscience (2024): 1-8.

2.Schuur, Edward AG, et al. "Climate change and the permafrost carbon feedback." Nature 520.7546 (2015): 171-179.

3.Legendre, Matthieu, et al. "Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology." Proceedings of the National Academy of Sciences 111.11 (2014): 4274-4279.