“Missing link” of RNA viruses found in oceans could detect emerging viral threats

What is the research about?

RNA viruses are responsible for a range of human diseases, from the common cold to COVID-19, and they can also infect plants and animals in ways that affect our lives. But RNA viruses have been less well studied than DNA ones.

The viruses identified and the tools developed in the study could help researchers to catalogue new viruses as genetic databases grow.

RNA viruses lack a kind of genetic bar code that helps us hunt down DNA viruses, but a group of researchers in Science looked for the gene that codes for a protein that allows the virus to replicate – all RNA viruses have this protein in common. Their aim was to find similarities in gene sequences that could offer insight into the evolution of RNA viruses.

What did the researchers do?

They screened a global database of RNA sequences from plankton – aquatic organisms that are common hosts for RNA viruses – collected during a four-year global research project. The screening identified more than 44,000 genes that code for the virus protein. Then they used artificial intelligence to systematically organise these sequences to find similarities between the genes, as that would indicate how closely related they are.

What did they find?

They identified a total of 5,504 new marine RNA viruses and doubled the number of known RNA virus phyla (primary grouping) from five to ten.

Mapping these new sequences geographically showed that two of the new phyla were abundant across vast oceanic regions, one in temperate and tropical waters (the Taraviricota, named after the Tara Oceans expeditions) or the Arctic Ocean (the Arctiviricota).

The scientists believe that Taraviricota might be the long sought-after missing link in the evolution of RNA viruses that connects two different known branches of RNA viruses that diverged in how they replicate.

What does this mean?

RNA viruses can infect a range of organisms, including, say the researchers “microbes that influence environments and food webs at the chemical level”.

The viruses identified and the tools developed in the study could help researchers to catalogue new viruses as genetic databases grow.

The researchers say that despite identifying so many new RNA viruses, “it remains challenging to pinpoint what organisms they infect”. Studying their genomes in greater detail would help scientists to understand better how these viruses work.