SNDV, a novel virus of the extremely thermophilic and acidophilic archaeon Sulfolobus

We describe a novel virus, SNDV (Sulfolobus neozealandicus droplet-shaped virus), of the crenarchaeotal archaeon Sulfolobus, which was found in a carrier state in a Sulfolobus strain isolated from a field sample from New Zealand. SNDV particles are droplet-shaped and densely covered by thin tail fibers at their pointed ends. The virion consists of a core and a coat. The latter has the appearance of a beehive and has a surface that is either helically ribbed or a stack of hoops. The genome is cccDNA of 20 kb, which is modified by dam-like methylation. It is cleaved by only a few type II restriction enzymes e.g., DpnI but not MboI, demonstrating an N(6)-methylation of the adenine residue in GATC sequences. The DNA-modifying system differentiates between virus and host. We postulate a virus-encoded methylase that is active on hemimethylated DNA. The host range of SNDV is confined to few Sulfolobus strains from New Zealand. The virus persists in an unstable carrier state rather than as a prophage. Due to its uniqueness we propose to assign it to a novel virus family termed Guttaviridae.