Virus classification
Group: Group I (dsDNA)
Order: Caudovirales
Family: Siphoviridae
  • Styloviridae[1]

Siphoviridae is a family of double-stranded DNA viruses in the order Caudovirales. Bacteria and archaebacteria serve as natural hosts. There are currently 313 species in this family, divided among 47 genera.[2][3] The characteristic structural features of this family are a nonenveloped head and noncontractile tail.


Viruses in 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 50kb in length,[2] 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.[2] Bacteria and archeabacteria serve as the natural host. Transmission routes are passive diffusion.[2]


Group: dsDNA


Proposed genera

Electron micrographs of siphovirus from P. 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 organisation of genes in the genera L5likevirus, Lambdalikevirus, Phic3unalikevirus, and Psimunalikevirus and the proposed genera Sfi2likevirus, Sfi1likevirus, Sk1likevirus, and Tm4likevirus suggests that these may form a lambda supergroup (or subfamily).[5]

The following genera have been proposed but are not currently ratified by the International Committee on Taxonomy of Viruses:[6][7][8][9][10][11]


In addition to the above viruses, many members of Siphoviridae have been grouped into an unclassified group with no genus assignment.[12] This group includes numerous phages known to infect Lactobacillus, Mycobacterium, Streptococcus, and other bacteria.


  1. Safferman, R.S.; Cannon, R.E.; Desjardins, P.R.; Gromov, B.V.; Haselkorn, R.; Sherman, L.A.; Shilo, M. "Classification and Nomenclature of Viruses of Cyanobacteria". Intervirology. 19 (2): 61–66. doi:10.1159/000149339.
  2. 1 2 3 4 5 6 "Viral Zone". ExPASy. Retrieved 1 July 2015.
  3. 1 2 ICTV. "Virus Taxonomy: 2014 Release". Retrieved 1 July 2015.
  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 2533672Freely accessible. PMID 18702830.
  5. Brüssow H, Desiere F (2001). "Comparative phage genomics and the evolution of Siphoviridae: insights from dairy phages". Mol Microbiol. 39 (2): 213–22. doi:10.1046/j.1365-2958.2001.02228.x.
  6. "The Dilemma of Phage Taxonomy Illustrated by Comparative Genomics of Sfi21-Like Siphoviridae in Lactic Acid Bacteria". Journal of Bacteriology. September 2014. doi:10.1128/JB.184.21.6026-6036.2002.
  7. "Three proposed new bacteriophage genera of staphylococcal phages: "3alikevirus", "77likevirus" and "Phietalikevirus"". Archives of Virology. 11 Sep 2013. doi:10.1007/s00705-013-1833-1.
  8. Taxonomy Proposals Awaiting Ratification at ICTV
  9. Taxonomy Proposals Pending at ICTV
  10. Holmfeldt, K.; Solonenko, N.; Shah, M.; Corrier, K.; Riemann, L.; Verberkmoes, N. C.; Sullivan, M. B. (2013). "Twelve previously unknown phage genera are ubiquitous in global oceans". Proceedings of the National Academy of Sciences. 110 (31): 12798. doi:10.1073/pnas.1305956110.
  11. Niu, Y. D.; McAllister, T. A.; Nash, J. H. E.; Kropinski, A. M.; Stanford, K. (2014). "Four Escherichia coli O157:H7 Phages: A New Bacteriophage Genus and Taxonomic Classification of T1-Like Phages". PLoS ONE. 9 (6): e100426. doi:10.1371/journal.pone.0100426.
  12. "unclassified Siphoviridae". NCBI Taxonomy.
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