Strange viruses that populate the oceans in abundance, likely distant cousins of the herpesvirus, have been discovered thanks to data collected by an expedition led by scientific schooner Tara Oceans, according to a study published Wednesday.
Baptized mirusviruses (“mirus” means “strange” in Latin), these DNA viruses are present on the surface of Earth’s seas and oceans, from the equator to the poles, where they infect plankton.
“These are chimeric viruses, halfway between the giant viruses, which are also abundant in the oceans, where they only infect protozoa, and the herpesvirus, which only infects animals whose humans are,” describes biologist Tom Delmont, CNRS researcher and Author of study published in Nature.
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The unexpected discovery was made at the Genoscope in Evry (in the Paris region), where the genomes collected by Tara Océans are being sequenced.
“We were studying the 2009-2013 expedition data tsunami of 300 billion DNA sequences when we encountered an unusual evolutionary signal,” the specialist told AFP.
herpes virus | BSIP over AFP
This signal was that of a marker gene carried by giant viruses, but also by mirus viruses. “It was as if we had found treasure on a huge sandy beach with a metal detector,” the researcher continues.
After several years of analysis, scientists from the Tara Oceans consortium and their collaborators were able to characterize this new group of very complex and diverse viruses.
The discovery will allow a better understanding of ocean biodiversity and the importance of viruses in these ecosystems. “We only see viruses as diseases, but their presence in the oceans is natural and beneficial – a bit like our gut microbiota,” says Tom Delmont.
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“By infecting the cells, they destroy them and that brings nutrients back into the ecosystem. This enables a renewal of plankton activity,” the biologist explains.
These viruses also have an amazing evolutionary history because the peculiar makeup of their genome suggests they are “distant cousins” of herpes.
Herpesviruses are widespread in animals, infecting more than half of the world’s population. However, they are completely absent in unicellular marine organisms, and researchers wondered why.
“The puzzle could be solved as follows: thanks to mirusviruses, we imagine what the oceanic ancestor of herpes might have been. This ancestor would have infected protozoa in the oceans millions of years ago before specializing in infecting animals,” says the researcher.