Adnaviria: a New Realm for Archaeal Filamentous Viruses with Linear A-Form Double-Stranded DNA Genomes

The International Committee on Taxonomy of Viruses (ICTV) has recently introduced a comprehensive hierarchical system for classifying viruses, with realms being the highest ranks. These realms are considered monophyletic, though each is thought to have originated independently of others. As part of this effort, a new realm called Adnaviria has been established, which brings together archaeal filamentous viruses that feature linear A-form double-stranded DNA genomes and distinct major capsid proteins that are unrelated to those found in other known viruses. This new classification includes viruses from families such as Ligamenvirales, Lipothrixviridae, Rudiviridae, Tokiviricetes, and Tristromaviridae, and is particularly significant for hyperthermophilic archaea. The creation of Adnaviria highlights the complexity of virus taxonomy, shedding light on virus evolution, structure and assembly, and advancing our understanding of viral diversity and virus classification.