A strange virus that is abundant in the oceans, probably a distant relative of the herpes virus, was discovered thanks to data collected by the schooner Tara expedition, according to a study published on Wednesday, quoted by AFP.

This type of DNA virus, called mirusvirus (“mirus” is Latin for “strange”), is present on the surface of the world’s seas and oceans, from the equator to the poles, where it infects plankton.

They are “chemicals” intermediate between the giant ones, which are also abundant in the oceans, where they infect only single-celled organisms, and the herpes virus, which “only infects animals, including humans”, describes biologist Tom Delmont, CNRS researcher and author of the study published in the journal Nature.

The unexpected discovery was made at the Genoscope in Evres (near Paris), where the genomes collected by Tara Oceans are being sequenced.

We were examining the ‘tsunami’ of data from the 2009-2013 expedition of 300 billion DNA sequences when we came across an unusual evolutionary signal,” the microbial ecology expert told AFP.

This signal was a marker gene signal carried by giant viruses as well as viruviruses. “It was like finding treasure on a huge sandy beach with a metal detector,” the researcher continues.

After several years of analysis, Tara Oceans Consortium scientists and their collaborators have succeeded in characterizing this new group of highly complex and diverse viruses.

The discovery will lead to a better understanding of ocean biodiversity and the importance of viruses in these ecosystems. “We think of different types of viruses as just diseases, but their presence in the oceans is natural and beneficial — similar to our gut microbiota,” says Tom Delmont.

“By infecting cells, they destroy them, and that puts nutrients back into the ecosystem. This makes it possible to restore plankton activity,” the biologist explains.

These groups of viruses also have a surprising evolutionary history, as the special composition of their genomes suggests that they are “distant relatives” of herpes.

Herpes viruses are widespread among animals and infect more than half of the world’s population. But they are completely absent in single-celled marine organisms, and researchers wondered why.

“The mystery can be clarified as follows: thanks to mirusviruses, we can imagine what the oceanic ancestor of herpes could have been like. This ancestor could have infected single-celled organisms in the oceans millions of years ago before specializing in infecting animals,” says the researcher.