An analysis of the genetic material in the sea identified thousands of previously unknown RNA viruses and doubled the number of systems, or biological groups, of viruses thought to exist, according to a new study published by our team of researchers in the journal Science
An analysis of the genetic material in the sea identified thousands of previously unknown RNA viruses and doubled the number of systems, or biological groups, of viruses thought to exist, according to a new study published by our team of researchers in the journal Science.
RNA viruses are best known for the diseases they cause in people, from the common cold to the coronavirus. They also harm plants and animals that are important to humans.
These viruses carry their genetic information in RNA instead of DNA. RNA viruses evolve at a much faster rate than DNA viruses. Scientists have cataloged hundreds of thousands of DNA viruses in their natural environments, but RNA viruses have been relatively unstudied.
There are more RNA viruses in the sea than researchers previously thought.
Guillermo Domínguez Huerta, CC BY-ND
But unlike humans and other organisms composed of cells, viruses do not have unique short stretches of DNA that can serve as what researchers call a "genetic barcode." Without this barcode, it is difficult to differentiate between different species of viruses in nature.
To get around this limitation, we decided to identify the gene that codes for a certain protein that allows the virus to replicate its genetic material. It is the only protein that all RNA viruses have in common, because it plays a vital role in how they reproduce. In each RNA virus, however, there are small differences in the gene that codes for the protein, and they can help distinguish between types of viruses.
We scanned a global database of RNA sequences from plankton collected over the four years of the Tara Oceans Expeditions Global Research Project. Plankton is the common name for any marine organism that is too small to swim against the current. They are an essential part of marine food webs and common hosts of RNA viruses. Our scan ultimately identified more than 44,000 protein-coding genes for the viruses.
Our next challenge was to determine the evolutionary relationships between these genes. The more similar two genes are, the more likely viruses with those genes are closely related. Because these sequences evolved so long ago (perhaps before the first cell), the genetic landmarks indicating where new viruses may have diverged from a common ancestor have been lost over time. But a form of artificial intelligence called machine learning has allowed us to systematically arrange these sequences and identify differences more objectively than if the task had been done manually.
We identified a total of 5,504 new marine RNA viruses and doubled the number of known RNA virus systems from five to ten. GG mapping of these new sequences revealed that two of the new systems are particularly abundant in large ocean regions, with regional preferences for temperate and tropical waters (Taraviricota, named after the Tara Oceans expeditions) or the Atlantic Ocean (Arctiviricota).
For an article in The Conversation
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