Virologists Identify More Than 5,000 New Viruses in the Ocean

The new study focused on under-researched RNA viruses, which often infect animals and humans

An image of ocean water taken from above the surface. The water is blue and rippled.
Mapping out where these RNA viruses are found globally can help scientists understand how they interact with organisms driving the planet's ecological processes. DevizK via Wikimedia Commons under CC BY-SA 4.0

Virologists have identified 5,504 new virus species floating in ocean water samples. The viruses were found using a machine learning algorithm to study 35,000 water samples from all over the globe, reports Vishwam Sankaran for the Independent.

Researchers suspect only a tiny portion of viruses that can harm animals, plants, and humans have been studied. The find may reshape scientists' understanding of how these submicroscopic infectious agents drive ecological processes in the planet's oceans. Details of the study were published this month in Science.

Most well-studied viruses are viruses that contain DNA as their genetic material; viruses identified in the new study are RNA viruses, reports Rachael Rettner for Live Science

"RNA viruses are best known for the diseases they cause in people, ranging from the common cold to COVID-19. They also infect plants and animals important to people," study authors write in a blog post for The Conversation. "RNA viruses evolve at much quicker rates than DNA viruses do. While scientists have cataloged hundreds of thousands of DNA viruses in their natural ecosystems, RNA viruses have been relatively unstudied."

During a four-year-long Tara Oceans global research project, the team collected RNA sequences from plankton. Plankton are aquatic organisms crucial to ocean food webs and commonly host RNA viruses, per the The Conversation. An analysis narrowed the RNA sequences down to ones that contained the RdRp gene, which is needed for virus replication. For billions of years, this gene evolved in RNA viruses and is not found in other types of viruses or cells, per the Independent.

"RNA viruses are clearly important in our world, but we usually only study a tiny slice of them – the few hundred that harm humans, plants, and animals. We wanted to systematically study them on a very big scale and explore an environment no one had looked at deeply, and we got lucky because virtually every species was new, and many were really new," says study author Matthew Sullivan, an Ohio State University microbiologist, in a statement.

However, because the RdRp gene dates to when life was first detected on Earth, the positioning of the sequence has changed many times, which made relying on a phylogenetic tree alone to identify the sequences was near impossible, a statement explains.

Using machine learning to organize the data, the team found 5,504 new RNA virus species that were grouped into five existing RNA virus phyla or levels of classification. With so many new viruses identified, the team proposed five additional classification categories.

The five known RNA virus phyla are within the Orthornavirae kingdom. However, researchers proposed five new classifications for some of the new viruses that don't fit into the existing five phyla with the discovery. The new phyla include TaraviricotaPomiviricota, ParaxenoviricotaWamoviricota and Arctiviricota, per a statement. Most of the newly identified species belong to a new proposed phylum called Taraviricota.

"There's so much new diversity here – and an entire phylum, the Taraviricota, were found all over the oceans, which suggests they're ecologically important," Sullivan explains in a statement.

After mapping the genetic sequences geographically, the team found that the new phylum, Taraviricota (named after the Tara Oceans expedition) was more abundant in temperate and tropical waters. In contrast, the Arctiviticota was found in the Arctic Ocean, the Conversation reports. The team also suspects that Taraviricota may be the missing link in the evolution of RNA viruses that connect two branches of RNA viruses that diverged based on how they replicate. 

Overall, the new find could help virologists understand the evolutionary history of RNA viruses—and even provide a glimpse into how early life on Earth evolved. By further mapping out where these RNA viruses are found, scientists can understand how the viruses interact with other organisms on Earth, per the Conversation

"RdRp is supposed to be one of the most ancient genes – it existed before there was a need for DNA. So, we're not just tracing the origins of viruses, but also tracing the origins of life," says study author Ahmed Zayed, also a microbiologist at Ohio State University, in a statement.