

Classification and Host Range
- Family: Fuselloviridae
- Host Range: Primarily infects Sulfolobus species (e.g., S. shibatae, S. solfataricus, S. islandicus).
- Distribution: Ubiquitous in high-temperature (≥70°C) and acidic (pH ≤4) hot springs worldwide.
- Taxonomy: Contains two genera:
- Alphafusellovirus: Includes seven species (e.g., Sulfolobus spindle-shaped virus 1-9).
- Betafusellovirus: Includes two species (e.g., Acidianus spindle-shaped virus 1, Sulfolobus spindle-shaped virus 6).

Virion Structure and Genome
- Morphology: Enveloped, lemon-shaped virions.
- Size: Approximately 60 nm in diameter and 100 nm in length.
- Genome: Double-stranded circular DNA, around 17.3 kb.
- Virion Composition:
- Four virus-encoded structural proteins (VP1-VP4).
- One DNA-binding chromatin protein of cellular origin.
- Post-translational modifications: Glycosylation of VP1, VP3, and VP4. Proteolytic processing of VP1.
- Lipid content: Contains glycerol dibiphytanyl glycerol tetraether (GDGT) lipids acquired from the host membrane.