Bizarre, never-before-seen viruses discovered thriving throughout the world's oceans

Mirusviruses regulate the activity of plankton and contribute to the health of the marine ecosystems. (Image credit: Shutterstock)

Scientists have discovered never-before-seen viruses that thrive in sunlit oceans from pole to pole and infect plankton. They dubbed the newfound microbes "mirusviruses" — "mirus" meaning "strange" in Latin.

The researchers concluded that mirusviruses belong to a large group of viruses called Duplodnaviria, which includes the herpesviruses that infect animals and humans, based on shared genes that encode the shell, or "particle" enclosing their DNA. But the strange, newfound viruses also share a staggering number of genes with a group of giant viruses, called Varidnaviria.

This suggests that mirusviruses are a bizarre hybrid between two distantly related viral lineages, the scientists concluded.

"They seem to be an extremely unusual group of viruses," Tom Delmont, a researcher at the French National Centre for Scientific Research (CNRS) who participated in the discovery, told Live Science. "This is why we consider them as being chimeric, because they are a mix of two different groups of viruses — on one side the herpesviruses, based on the particle genes, and on the other side the giant viruses, based on many more genes."

The team described the strange, newfound viruses in a study published Wednesday (April 19) in the journal Nature. The discovery highlights how little we know about the viruses lurking in Earth's oceans.

Related: Scientists discover viruses that secretly rule the world's oceans

To find the viruses, the team pored over data from the Tara Ocean expedition, which collected nearly 35,000 ocean water samples containing viruses, algae and plankton between 2009 and 2013. The researchers then searched for evolutionary clues in millions of microbes' genes.

"Working on this data is like surveying a huge area of sand with a metal detector, looking for a treasure," Delmont said. "We found an evolutionary treasure."

In combing through this data trove, the scientists detected a previously undescribed lineage of double-stranded DNA viruses, the mirusviruses, that can be found in the sunlit surface waters of polar, temperate and tropical oceans. These abundant viruses infect plankton, which are tiny organisms that drift on ocean currents and can produce spectacular blooms visible from space, according to the National Ocean Service

By invading the plankton's cells, mirusviruses likely help regulate the microorganisms' activity and thus the flow of carbon and nutrients through the ocean.

"Viruses are a very natural component of plankton at the surface of the ocean," Delmont said. "They are going to destroy many, many cells every day and this is going to release nutrients, particles inside the cells that are going to be used by other cells to be active and healthy."

Mirusviruses may be the key to resolving the enigmatic origin of herpes viruses, Delmont said. The genes encoding the protective shell around viral DNA are strikingly similar in both groups, suggesting that they are related.

"This means that there is a shared evolutionary history between herpes, that infect only animals, and the mirusviruses that are everywhere in the ocean, where they infect unicellular organisms," Delmont said. "All of this is pointing to a planktonic origin for herpes."

These unusual viruses represent a new front for research into microbial life in our oceans and there are many more discoveries in store, Delmont said.

"We will be trying to isolate mirusviruses in the coming year," co-author Hiroyuki Ogata, a professor at the Institute for Chemical Research at Kyoto University, told Live Science in an email. "Isolation is now essential to uncover the mystery of this new viral [group]."

Sascha Pare
Trainee staff writer

Sascha is a U.K.-based trainee staff writer at Live Science. She holds a bachelor’s degree in biology from the University of Southampton in England and a master’s degree in science communication from Imperial College London. Her work has appeared in The Guardian and the health website Zoe. Besides writing, she enjoys playing tennis, bread-making and browsing second-hand shops for hidden gems.

  • Hartmann352
    Viruses that were trapped in frozen arctic permafrost, preserved since the Ice Age thousands of years ago, can potentially make contact with humans (Mohan, 2014). Viruses enter host cells by penetrating through the cellular membranes, attaching to receptors, changing its viral proteins. In the end, the virus transfers its viral genomes inside host cells. Scientists are most concerned about the undiscovered capabilities of these ancient viruses which we may not have any natural immunity to.

    Discovery of the Mollivirus sibericum
    The presence of the frozen viruses was first made known to the public in 2015; researchers Chantal Abergel and Jean-Michel Claverie of the French Centre National de la Recherche Scientifique uncovered the Mollivirus sibericum in 30,000 year old permafrost, and as they put it in their paper, “The fact that two different viruses retain their infectivity in prehistorical permafrost layers should be of concern in a context of global warming” (Wei, 2018).

    The microbe, described in the Proceedings of the National Academy of Sciences, appears to belong to a family of mega-viruses that exclusively infect amoebas, but its revival stands as “a proof of principle that we could eventually resurrect active infectious viruses from different periods,” said the study’s lead author, Jean-Michel Claverie (Mohan, 2014). The Mollivirus sibericum was visibly large under the microscope and it consisted of a significant amount of genetic material.

    A study in Alaskan permafrost was undertaken to learn more about the discovery and the potential impacts of global warming and permafrost thawing on metabolic pathways (Mooney, 2015). The researchers tested soils before and after thawing and found a rapid increase in activity after thawing due to the decomposition of soil organic matter. The thawing of permafrost leads to increased microbial activity and, as a result, increased emissions of greenhouse gases such as CO2, CH4, and N2O, which were previously trapped within (Collins, 2019). The increased methane emission resulted in a tenfold increase in the number of methanogenic archaea, as well as large changes in the composition and operations of archaeal communities.

    Conclusion and Further Research
    Although this was a groundbreaking discovery, this does not signify that it is likely for these viruses to use humans as their host organism. “All viruses tend to be very specific about their host species, so there is essentially no chance that the viruses they discovered will have any impact on human health,” stated Grant McFadden, a professor of molecular genetics and microbiology at the University of Florida and the former president of the American Society for Virology (Mooney, 2015). In addition, more research needs to be done in order to rule out the possibility that they could survive this long-term freezing and still infect their host, though it is questionable that they can last tens of thousands of years without a host.

    A more pressing issue of this impact on pathology is the threat of the spread of vector-borne diseases, much less the melting permafrost. Organisms tend to migrate and follow unusual travel behavior in an environment where the temperature and climate are unstable. McFadden states that, “the wider global spread of insect vectors (particularly mosquitoes) and the viral pathogens they carry, compared to the real threat caused by ever increasing geographic ranges of vector-borne diseases like Dengue and Chikungunya viruses, the threat to human health of re-animated viruses from thawing permafrost is vanishingly small” (Wei, 2018).

    References and Sources

    Geoffrey Mohan. (2014). Ancient, frozen mega-virus is revived; If 30,000 years in Siberian permafrost didn’t kill it, human pathogens may lurk too, researchers say. The Los Angeles Times.

    Margesin, R., & Collins, T. (2019). Microbial ecology of the cryosphere (glacial and permafrost habitats): current knowledge. Applied Microbiology and Biotechnology, 103(6), 2537–2549.

    Chris Mooney. (2015). Why you shouldn’t freak out about ancient “Frankenviruses” emerging from Arctic permafrost: Of all the pandemic health risks we face, ancient Arctic viruses rank pretty low, say scientists. In Washington Post – Blogs. WP Company LLC d/b/a The Washington Post.

    Wei, SP, Cui, HP, Zhu, YH, Lu, ZQ, Pang, SJ, Zhang, S, Dong, HL, Su, X: Shifts of methanogenic communities in response to permafrost thaw results in rising methane emissions and soil property changes. vol. 22, issue 3, pp. 447-459. Extremophiles (2018)

    Permafrost — ground that remains frozen for more than two years straight — underlies nearly one-quarter of the land in the northern hemisphere. The deepest parts extend a mile into the Earth, and the oldest parts are more than 600,000 years old. The permanence of the permafrost is being undermined in many places, including Canada, Alaska and Siberia by local climate changes, mining and economic development.