A totally new type of virus has been found living on the sunlit surface of the seas and oceans. Dubbed mirusviruses – "mirus" meaning wonderful or strange in Latin – the microbes are related to both giant viruses and herpesviruses. As such, the discovery might help to illuminate the murky evolutionary history of herpes.
In a new study, scientists detailed the discovery of mirusviruses and explain that they belong to a realm of viruses called Duplodnaviria. This is a large type of double-stranded DNA viruses that includes herpesviruses like the herpes simplex virus.
Fortunately for us, mirusviruses are not interested in humans and tend to only infect single-celled plankton. This does suggest, however, that the ancestors of herpesviruses once infected marine single-cell organisms. That’s a fairly humble beginning considering that herpes has since managed to infect half of humanity.
Although their evolutionary heritage links back to herpesviruses, the majority of mirusvirus genes are similar to those of giant viruses (literally just really big viruses). Nevertheless, the researchers say this never-before-seen band of viruses is pretty unique.
“Mirusviruses substantially deviate from all other previously characterized groups of DNA viruses,” the study authors conclude.
“The discovery of Mirusviricota is a reminder that we have not yet grasped the full ecological and evolutionary complexity of even the most abundant double-stranded DNA viruses in key ecosystems such as the surface of our oceans and seas,” they add.
The new viruses were found by trawling through data gathered by the Tara Ocean expedition. This project collected over 35,000 samples of viruses, algae, and plankton from over 200 different locations worldwide.
They also sequenced their genetic material, providing scientists with a plethora of data to pore over – and plenty of opportunities to discover new species.
“In 2019, our research team observed an unusual evolutionary signal in the massive amounts of sequencing data provided by the Tara Oceans project. By tracking this signal, we discovered and then characterized a major DNA virus group: mirusviruses. The publication of this discovery in Nature marks the start of a new adventure and a gateway for the scientific community to detect and study mirusviruses in any number of ecosystems,” Tom Delmont, study author and expert in microbial ecology at the French National Center for Scientific Research, said in a statement.
“Tara Oceans has transformed our understanding of plankton ecology. Our study proves that this incredible expedition also provides answers to fundamental evolutionary questions. Much remains to be discovered and understood about mirusviruses. They have yet to be cultivated, no images of their viral particle exist, and we have yet to study them in places other than the oceans!” added Morgan Gaïa, study first author.
The study is published in the journal Nature.