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Typical structure of a siphovirus
Virus classification
Group: Group I (dsDNA)
Order: Caudovirales
Family: Siphoviridae
  • see below
  • Styloviridae[1]

Siphoviridae are a family of double-stranded DNA viruses infecting only bacteria. These viruses may also be referred to as bacteriophages. The characteristic structural features of this family are a nonenveloped head and noncontractile tail.


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.[2]

Virions of viruses in this family have an icosahedral capsid (morphotype B1) or a prolate capsid (morphotype B2). These capsids have no envelope and are generally about 60 nanometers in diameter. Members of this family are also characterized by their filamentous, cross-banded, noncontractile tails, usually with short terminal and subterminal fibers.

The genome of Siphoviridae phages is double stranded and linear. It is typically about 50 kilobases in length and contains about 70 genes. The guanine/cytosine content is usually around 52%.


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).[3]

The c2-like viruses have oblate heads.

The following viruses have been classified into genera:[3][4][5]

Other genera awaiting classification into subfamilies:

Proposed genera[edit]

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]

  • Genus Cba39unalikevirus; type species: Cellulophaga phage phi39:1
    • Species:
      • Cellulophaga phage phi39:1
  • Genus Cba46unalikevirus; type species: Cellulophaga phage phi46:1
    • Species:
      • Cellulophaga phage phi46:1
  • Genus Cba18unalikevirus; type species: Cellulophaga phage phi18:1
    • Species:
      • Cellulophaga phage phi18:1
      • Cellulophaga phage phi12:1
      • Cellulophaga phage phi12:3
      • Cellulophaga phage phi17:1
      • Cellulophaga phage phi18:2
  • Genus Cba10unalikevirus; type species: Cellulophaga phage phi10:1
    • Species:
      • Cellulophaga phage phi10:1
      • Cellulophaga phage phi19:1
  • Genus Cba13unalikevirus; type species: Cellulophaga phage phi13:1
    • Species:
      • Cellulophaga phage phi13:1
      • Cellulophaga phage phi19:2
      • Cellulophaga phage phiST
  • Genus Jk06likevirus; type species: Escherichia phage Jk06
    • Species
      • Escherichia phage Eb49
      • Escherichia phage Jk06
      • Escherichia phage Rogue1
      • Escherichia phage AHP24
      • Escherichia phage AHS24
      • Escherichia phage AHP42
      • Escherichia phage AKS96
      • Enterobacteria phage phiJLA23
      • Enterobacteria phage phiKP26
  • Genus Kp36likevirus; type species: Klebsiella phage KP36
    • Species
      • Enterobacter phage F20
      • Klebsiella phage KP36
  • Genus R1tlikevirus; type species: Lactococcus phage r1t
    • Species
      • Lactococcus phage r1t
  • Genus Rtplikevirus; type species: Escherichia phage Rtp
    • Species
      • Escherichia phage Rtp
      • Enterobacteria phage vB_EcoS_ACG-M12
  • Genus Tlslikevirus; type species: Escherichia phage Tls
    • Species
      • Escherichia phage Tls
      • Salmonella phage FSL SP-126


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. ^ 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. 
  3. ^ a b 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. 
  4. ^ NCBI Taxonomy (Siphoviridae)
  5. ^ International Committee on Taxonomy of Viruses
  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.  edit
  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.  edit
  12. ^ "unclassified Siphoviridae". NCBI Taxonomy. 

External links[edit]