SNDV, a novel virus of the extremely thermophilic and acidophilic archaeonSulfolobus

We describe a novel virus, SNDV (Sulfolobus neozealandicus droplet-shaped v irus), of the crenarchaeotal archaeon Sulfolobus, which was found in a carr ier state in a Sulfolobus strain isolated from a field sample from New Zeal and. SNDV particles are droplet-shaped and densely covered by thin tail fib ers at their pointed ends. The virion consists of a core and a coat. The la tter has the appearance of a beehive and has a surface that is either helic ally ribbed or a stack of hoops. The genome is cccDNA of 20 kb, which is mo dified by dam-like methylation. It is cleaved by only a few type II restric tion enzymes e.g., Dpn1 but not Mbol, demonstrating an N(6)-methylation of the adenine residue in GATC sequences. The DNA-modifying system differentia tes 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 Sul folobus strains from New Zealand. The virus persists in an unstable carrier state rather than as a prophage. Due to its uniqueness we propose to assig n it to a novel virus family termed Guttaviridae. (C) 2000 Academic Press.