Baku, April 11, AZERTACMore than 5,000 new virus species have been identified in the world's oceans, according to a new study.The study researchers analyzed tens of thousands of water samples from around the globe, hunting for RNA viruses, or viruses that use RNA as their genetic material. The novel coronavirus, for instance, is a type of RNA virus. These viruses are understudied compared with DNA viruses, which use DNA as their genetic material, the authors said.The diversity of the newfound viruses was so great that the researchers have proposed doubling the number of taxonomic groups needed to classify RNA viruses, from the existing five phyla to 10 phyla. (Phylum is a broad classification in biology just below "kingdom.")For the study, published on April 7 in the journal Science, 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 to study the impact of climate change on the ocean.They examined genetic sequences extracted from small aquatic organisms known as plankton, which are common hosts for RNA viruses, the researchers said. They homed in on sequences belonging to RNA viruses by looking for an ancient gene called RdRp, which is found in all RNA viruses but is absent from other viruses and cells. They identified over 44,000 sequences with this gene.But the RdRp gene is billions of years old, and it has evolved many times. Because the gene's evolution goes so far back, it was difficult for the researchers to determine the evolutionary relationship between the sequences. So the researchers used machine learning to help organize them.Overall, they identified about 5,500 new RNA virus species that fell into the five existing phyla, as well as the five newly proposed phyla, which the researchers named Taraviricota, Pomiviricota, Paraxenoviricota, Wamoviricota and Arctiviricota.Virus species in the Taraviricota phylum were particularly abundant in temperate and tropical waters, while viruses in the Arctiviricota phylum are abundant in the Arctic Ocean, the researchers wrote in The Conversation.(opens in new tab)Understanding how the RdRp gene diverged over time could lead to a better understanding of how early life evolved on Earth, the authors said.