According to a new study, over 5,000 new virus species have been discovered in the world's oceans. The researchers examined tens of thousands of water samples from all over the world in search of RNA viruses, or viruses that use RNA as their genetic material.
The novel coronavirus, for example, is an RNA virus. According to the authors, these viruses are understudied in comparison to DNA viruses, which use DNA as their genetic material.
The diversity of the newly discovered viruses was so great that the researchers proposed doubling the number of taxonomic groups required to classify RNA viruses from five to ten. (In biology, a phylum is a broad classification that comes after "kingdom."
"There's so much new diversity here – and an entire [new] phylum, the Taraviricota, was found all over the oceans, which suggests they're ecologically important," said study lead author Matthew Sullivan, a professor of microbiology at The Ohio State University.
According to Sullivan, studies of RNA viruses have typically focused on those that cause disease. (Influenza, Ebola, and the coronavirus that causes pandemic are examples of well-known RNA viruses.) However, these are only a "tiny slice" of the RNA viruses on Earth, according to Sullivan.
"We wanted to study them systematically on a very large scale and explore an environment that no one had looked at deeply," Sullivan said in a statement.
The researchers analyzed 35,000 water samples taken from 121 locations in all five of the world's oceans. The researchers are part of the Tara Oceans Consortium, a global project that is investigating the effects of climate change on the ocean.
According to the researchers, they looked at genetic sequences extracted from plankton, which are small aquatic organisms that are common hosts for RNA viruses. They focused on RNA virus sequences by looking for an ancient gene called RdRp, which is found in all RNA viruses but not in other viruses or cells. They discovered over 44,000 sequences containing this gene.
However, the RdRp gene has been evolving for billions of years and has undergone numerous mutations. Because the gene's evolution dates back so far, the researchers had a difficult time determining the evolutionary relationship between the sequences. As a result, the researchers used machine learning to help them organize.
Overall, they discovered approximately 5,500 new RNA virus species belonging to the five existing phyla as well as the five newly proposed phyla, Taraviricota, Pomiviricota, Paraxenoviricota, Wamoviricota, and Arctiviricota.
Viruses from the Taraviricota phylum were particularly abundant in temperate and tropical waters, while viruses from the Arctiviricota phylum were abundant in the Arctic Ocean, according to the researchers, who published their findings in The Conversation.
According to the authors, understanding how the RdRp gene diverged over time could lead to a better understanding of how early life evolved on Earth.
"RdRp is thought to be one of the oldest genes- it existed before there was a need for DNA," study co-first author Ahmed Zayed, an Ohio State research scientist in microbiology, said in a statement. "As a result, we're not just tracing the origins of viruses, but also the origins of life."
