Exploration of ocean viruses uncovers Mirusviricota, sharing features with Herpesvirales

Researchers discover a new group of DNA viruses in the ocean that shares traits with herpesviruses and giant viruses, highlighting their potential impact on marine life and virus evolution. The study by Morgan Gaïa, Lingjie Meng and several others was published on April 19.

In the realm of marine virology, a significant stride has been made with the discovery of a potential new virus phylum, termed Mirusviricota, according to the study. This research, which utilized phylogenetic mapping and metagenomic sequencing of sunlit ocean waters, has uncovered a group of viruses that infect plankton and show a familial tie to herpesviruses. The study states that these viruses exhibit a genetic module for forming virions that are characteristics of the Duplodnaviria realm, hinting at a shared lineage with Herpesvirales. Yet, these oceanic viruses harbor a mix of genes that not only align with herpesviruses but also share a connection with the larger eukaryotic DNA viruses of the Varidnaviria realm, suggesting a complex evolutionary background.

According to the study, research of DNA viruses, particularly those that inhabit the ocean's photic zones, has yielded findings that extend beyond traditional classifications. A comprehensive analysis of environmental virus genomes has revealed a new clade that shows a unique genetic synthesis, merging traits of both the Duplodnaviria and Varidnaviria realms. The study states that this new group, encompassing over 100 mirusvirus genomes, boasts an extensive genome, with some sequences reaching up to 432 kilobases. Reportedly, these viruses are not only prolific but also exhibit a dynamic array of genetic functions, suggesting they play a prominent role in the infection processes of eukaryotic marine microorganisms. This evidence points to the mirusviruses' significant influence on marine ecology and the progression of eukaryotic DNA viruses.

The study states that scientists have charted a course that has led to the identification of Mirusviricota, a proposed new viral phylum. This endeavor, part of a larger metagenomic survey of oceanic plankton, harnessed nearly 300 billion metagenomic reads from various ocean expeditions. The meticulous research has not only broadened the known diversity of Nucleocytoviricota but has also spotlighted the mirusviruses' complex genetic composition and their widespread presence in marine environments. The study claims that this discovery fills a significant void in the knowledge of plankton ecology and sheds light on the evolutionary bond between herpesviruses and their distant viral relatives.

Nature: Morgan Gaïa, Lingjie Meng et al., Mirusviruses link herpesviruses to giant viruses, Nature (2023). https://doi.org/10.1038/s41586-023-05962-4