Siphoviridae

Siphoviridae
TME picture of an Escherichia virus HK97 virion, Siphoviridae
Virus classification
(unranked):	Virus
Realm:	Duplodnaviria
Kingdom:	Heunggongvirae
Phylum:	Uroviricota
Class:	Caudoviricetes
Order:	Caudovirales
Family:	Siphoviridae
Genera
see text
Synonyms
Styloviridae

Siphoviridae is a family of double-stranded DNA viruses in the order Caudovirales. Bacteria and archaea serve as natural hosts. There are 1,166 species in this family, assigned to 366 genera and 22 subfamilies. The characteristic structural features of this family are a nonenveloped head and noncontractile tail.

Structure

Typical structure of a siphovirus

Viruses in Siphoviridae are non-enveloped, with icosahedral and head-tail geometries (morphotype B1) or a prolate capsid (morphotype B2), and T=7 symmetry. The diameter is around 60 nm. 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, containing about 70 genes. The guanine/cytosine content is usually around 52%.

Life cycle

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. Bacteria and archaea serve as the natural host. Transmission routes are passive diffusion.

Taxonomy

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.

The following subfamilies are recognized:

The following genera are unassigned to a subfamily:

Please note that genus Inceonvirus is likely misspelled Incheonvirus.

External links

Wikispecies has information related to Siphoviridae.

• Viralzone: Siphoviridae
• ICTV
• Complete Genomes of Siphoviridae