According to a new study our research team published in the journal, an analysis of genetic material in the ocean has identified thousands of previously unknown RNA viruses and doubled the number of viral strains, or biological groups, thought to exist Science.
These viruses carry their genetic information in RNA, not DNA. RNA viruses develop much faster as DNA viruses. While scientists have catalogued Hundreds of thousands of DNA viruses In their natural ecosystems, RNA viruses are relatively unexplored.
However, unlike humans and other organisms made up of cells, viruses lack unique short stretches of DNA that could function as what researchers call a genetic barcode. Without this barcode, trying to distinguish different types of viruses in the wild can be difficult.
To circumvent this limitation, we decided to identify the gene that encodes a special protein which allows a virus to replicate its genetic material. It is the only protein that all RNA viruses have in common as it plays an essential role in the way they reproduce. However, each RNA virus has small differences in the gene that codes for the protein that can help distinguish one type of virus from another.
So we searched a global database of plankton RNA sequences collected over the four years Expeditions of the Tara Oceans global research project. Planktons are all aquatic organisms that are too small to swim against the current. They are an important part of the ocean food webs and frequent hosts for RNA viruses. Our screening eventually identified over 44,000 genes that code for the viral protein.
So our next challenge was to determine the evolutionary links between these genes. The more similar the two genes were, the more likely it was that viruses were closely related to those genes. Since these sequences had evolved so long ago (possibly before the first cell), the genetic guides that indicated where new viruses might have split from a common ancestor had been lost over time. However, a form of artificial intelligence called machine learning allowed us to organize these sequences in a systematic way and spot differences more objectively than if the task were done manually.
We identified a total of 5,504 new marine RNA viruses and doubled the number of known RNA virus strains from five to ten. Geographical mapping of these new sequences revealed that two of the new strains were particularly abundant in large oceanic regions, with regional preferences in both temperate and tropical waters (the Taraviricotanamed after the Tara Oceans Expeditions) or the Arctic Ocean (the arctiviricota).
we believe that Taraviricota may be the missing link in the evolution of RNA viruses that researchers have long sought, connecting two distinct known branches of RNA viruses that differ in their replication.
Why it matters
These new sequences help scientists better understand not only the evolutionary history of RNA viruses, but also the evolution of early life on Earth.
As the COVID-19 pandemic has shown, RNA viruses can cause deadly diseases. But RNA viruses also play a role important role in ecosystems because they can infect a wide range of organisms, including microbes affect the environment and food webs at the chemical level.
Mapping where in the world these RNA viruses live can help clarify how they affect the organisms that power many of the ecological processes that govern our planet. Our study also provides improved tools that can help researchers catalog new viruses as genetic databases grow.
What is not yet known
Although so many new RNA viruses have been identified, it remains difficult to determine which organisms they infect. Researchers are also present limited to mostly fragments of incomplete RNA virus genomes, in part due to their genetic complexity and technological limitations.
Our next steps would be to find out what types of genes might be missing and how they have changed over time. The discovery of these genes could help scientists better understand how these viruses work.