Siphoviridae

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Siphoviridae
Virus classification
Group: Group I (dsDNA)
Order: Caudovirales
Family: Siphoviridae
Genera
  • 3alikevirus
  • 77likevirus
  • C2likevirus
  • L5likevirus
  • Lambdalikevirus
  • N15likevirus
  • Phic3unalikevirus
  • Phietalikevirus
  • Psimunalikevirus
  • Spbetalikevirus
  • T5likevirus
  • Tunalikevirus
  • Yualikevirus

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.

Virology

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.[1]

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%.

Taxonomy


The organisation of genes in L5-, lambda-, phiC31-, psiM2-, Sfi21-, Sfi11-, sk1-, and TM4-like genera suggests that these may form a lamba supergroup (or subfamily).[1]

The c2-like viruses have oblate heads.

The following viruses have been classified into genera:[2]

  • Genus c2-like viruses; type species: Lactococcus phage c2
    • Species:
      • Lactococcus phage bIL67
      • Lactococcus phage c2
  • Genus Lambda-like viruses; type species: Enterobacteria phage lambda
    • Species:
      • Enterobacteria phage HK022
      • Enterobacteria phage HK97
      • Enterobacteria phage lambda
  • Genus N15-like viruses; type species: Enterobacteria phage N15
    • Species
      • Enterobacteria phage N15
  • Genus PhiC31-like viruses; type species: Streptomyces phage phiC31
    • Species
      • Streptomyces phage phiC31
  • Genus PsiM1-like viruses; type species: Methanobacterium phage psiM1
    • Species
      • Methanobacterium phage psiM1
  • Genus sk1-like viruses
    • Species
  • Genus Sfi11-like viruses
    • Species
  • Genus r1t-like viruses
    • Species
      • Lactococcus phage r1t
  • Genus Sfi21-like viruses
    • Species
      • Lactobacillus casei phage A2
      • Streptococcus thermophilus phage 7201
  • Genus SPbeta-like viruses; type species: Bacillus phage SPbeta
    • Species
      • Bacillus phage SPbeta
  • Genus T1-like viruses; type species: Enterobacteria phage T1
    • Species
      • Enterobacteria phage T1
  • Genus T5-like viruses; type species: Enterobacteria phage T5
    • Species:
      • Enterobacteria phage T5
      • Pectobacterium carotovorum subsp. carotovorum bacteriophage My1
      • Vibrio phage 149 (type IV)

Unclassified

In addition to the above viruses, many members of Siphoviridae have been grouped into an unclassified group with no genus assignment.[3] This group includes numerous phages known to infect Lactobacillus, Mycobacterium, Streptococcus, and other groups of bacteria.

References

  1. Brüssow H, Desiere F (2001) Comparative phage genomics and the evolution of Siphoviridae: insights from dairy phages. Mol Microbiol 39(2):213-22.
  2. http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=10699 NCBI Taxonomy (Siphoviridae)
  3. http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=196894&lvl=3&lin=f&keep=1&srchmode=1&unlock NCBI Taxonomy (unclassified Siphoviridae)

External links

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