By exploring data from Tara Ocean Foundation expeditions, scientists have discovered a new type of virus: mirusviruses. This discovery could make it possible to understand where herpes comes from and to better understand ocean biodiversity.
Strange viruses populate the oceans in abundance. Probable distant cousins of the herpes virus have been discovered thanks to data collected by an expedition from the scientific schooner Tara Ocean, according to a study published on Wednesday April 19. Called mirusviruses (“dead” means “odd” in Latin), these DNA viruses are present everywhere on the surface of the seas and oceans, from the equator to the poles, where they infect plankton. “These are chimeric viruses, halfway between the giant viruses, also abundant in the oceans where they only infect unicellular organisms, and the herpes virus, which only infects animals, whose humans»describes biologist Tom Delmont, CNRS researcher and author of the study published in Nature.
The unexpected discovery was made at the Genoscope in Evry (Essonne), where the genomes collected by the Tara Océan foundation are sequenced. “We were exploring the data tsunami from the 2009-2013 expedition, with 300 billion DNA sequences, when we came across an unusual evolutionary signal”, says the specialist in microbial ecology. The signal of a marker gene carried by giant viruses, but also by mirusviruses. “It was as if we had found a treasure on a huge sandy beach with a metal detector”, continues the researcher. After several years of analysis, scientists from the Tara Ocean consortium and their collaborators were able to characterize this new group of very complex and diverse viruses.
A natural and beneficial presence
The discovery will make it possible to better understand 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 – much like our gut microbiota”selon Tom Delmont. “By infecting the cells, they destroy them and that puts nutrients back into the ecosystem. This allows a renewal of plankton activity.develops the biologist.
These viruses also have an amazing evolutionary history because the particular composition of their genome suggests that they are “distant cousins” herpes. Herpes viruses are widespread in animals and infect more than half of the world’s human population. But they are completely absent from marine unicellular organisms. “The enigma could be clarified as follows: thanks to mirusviruses, we imagine what could be the oceanic ancestor of herpes. This ancestor would have infected single-celled organisms in the oceans millions of years ago, before specializing in the infection of animals.explains Tom Delmont.
