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TME picture of an Escherichia virus HK97 virion, Siphoviridae
Virus classification Edit this classification
(unranked): Virus
Realm: Duplodnaviria
Kingdom: Heunggongvirae
Phylum: Uroviricota
Class: Caudoviricetes
Order: Caudovirales
Family: Siphoviridae

see text

  • Styloviridae

Siphoviridae was a family of double-stranded DNA viruses in the order Caudovirales. The family Siphoviridae and order Caudovirales have now been abolished, with the term siphovirus now used to refer to the morphology of viruses in this former family . Bacteria and archaea serve as natural hosts. There was 1,166 species in this former family, assigned to 366 genera and 22 subfamilies.[2][3] The characteristic structural features of this family are a nonenveloped head and noncontractile tail.


Typical structure of a siphovirus

Viruses in the former family Siphoviridae are non-enveloped, with icosahedral and head-tail geometries[2] (morphotype B1) or a prolate capsid (morphotype B2), and T=7 symmetry. The diameter is around 60 nm.[2] Members of this family are also characterized by their filamentous, cross-banded, noncontractile tails, usually with short terminal and subterminal fibers. Genomes are double stranded and linear, around 50 kb in length,[2] containing about 70 genes. The guanine/cytosine content is usually around 52%.[citation needed]

Life cycle[edit]

Viral replication is cytoplasmic. Entry into the host cell is achieved by adsorption into the host cell. Replication follows the replicative transposition model. DNA-templated transcription is the method of transcription. Translation takes place by -1 ribosomal frameshifting, and +1 ribosomal frameshifting. The virus exits the host cell by lysis, and holin/endolysin/spanin proteins.[2] Bacteria and archaea serve as the natural host. Transmission routes are passive diffusion.[2]


Electron micrographs of siphovirus from Cutibacterium acnes (formerly Propionibacterium acnes). Phages were negatively stained and subjected to transmission electron microscopy. The phages have a head of approximately 55 nm in diameter, loaded with genetic material. Their tails have a size of 150 × 10 nm and are flexible and non-contractile. In the lower micrograph, PAD25 is adhering to bacterial cell debris, and two phages have lost their heads. All phages were classified as Siphoviruses based on their morphology.[4]

The following subfamilies are recognized:[3]

The following genera are unassigned to a subfamily:[3]

Please note that genus Inceonvirus is likely misspelled Incheonvirus.


  1. ^ Safferman, R.S.; Cannon, R.E.; Desjardins, P.R.; Gromov, B.V.; Haselkorn, R.; Sherman, L.A.; Shilo, M. (1983). "Classification and Nomenclature of Viruses of Cyanobacteria". Intervirology. 19 (2): 61–66. doi:10.1159/000149339. PMID 6408019.
  2. ^ a b c d e f "Viral Zone". ExPASy. Retrieved 1 July 2015.
  3. ^ a b c "Virus Taxonomy: 2020 Release". International Committee on Taxonomy of Viruses (ICTV). March 2021. Retrieved 12 May 2021.
  4. ^ Lood R, Mörgelin M, Holmberg A, Rasmussen M, Collin M (2008). "Inducible Siphoviruses in superficial and deep tissue isolates of Propionibacterium acnes". BMC Microbiol. 8: 139. doi:10.1186/1471-2180-8-139. PMC 2533672. PMID 18702830.

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