|Structural overview of the T4 phage|
|Group:||Group I (dsDNA)|
The Myoviridae is a family of bacteriophages. It has been divided into four subfamiles and eleven genera. Many species have not yet been assigned either a genus or a family. There are at least 130 species in this family.
These are nonenveloped viruses and consist of a head and a tail separated by a neck.
The head has a diameter of 50 - 110 nm and has icosahedral symmetry (T = 13 Q = 21). It is composed of 152 capsomers that are hexagonal in outline.
The tubular tail has helical symmetry and is 16-20 nm in diameter. It consists of a central tube, a contractile sheath, a collar, a base plate, six tail pins and six long fibers. It is similar to Tectiviridae, but differs in the fact that a myovirus' tail is permanent.
Contractions of the tail require ATP. On contraction of the sheath, sheath subunits slide over each other and the tail shortens to 10-15 nm in length.
The genome is linear, double-stranded DNA between 33.6-170 kilobases in length. It has terminally redundant sequences. The GC-content is ~35%. The genome encodes 200-300 proteins that are transcribed in operons.
Life cycle 
On attaching to a host cell, the virus uses its contractile sheath like a syringe, piercing the cell wall with its central tube and injecting the genetic material into the host. The injected DNA takes over the host cell's mechanisms for transcription and translation and begins to manufacture new viruses. Lysis occurs once the host resources are exhausted and the new viruses escape from the dead host cell.
The subfamily Teequatrovirinae is named after its type species Enterobacteria phage T4. Members of this subfamily are morphologically indistinguishable and have moderately elongated heads of about 110 nanometers (nm) in length, 114 nm long tails with a collar, base plates with short spikes and six long kinked tail fibers. The genera within this subfamily are divided on the basis of head morphology with the T4-like genus having a head length of 137 nm and those in the KVP40-like being 111 nm in length. Within the genera on the basis of protein homology the species have been divided into a number of groups.
The subfamily Peduovirinae have virions with heads of 60 nm in diameter and tails of 135 × 18 nm. These phages are easily identified because contracted sheaths tend to slide off the tail core. The P" phage is the type species.
The subfamily Spounavirinae are all virulent, broad-host range phages that infect members of the Firmicutes. They possess isometric heads of 87-94 nm in diameter and conspicuous capsomers, striated 140-219 nm long tails and a double base plate. At the tail tip are globular structures now know to be the base plate spikes and short kinked tail fibers with six-fold symmetry. Members of this group usually possess large (127–142 kb) nonpermuted genomes with 3.1–20 kb terminal redundancies. The name for this subfamily is derived from SPO plus una (Latin for one).
The haloviruses HF1 and HF2 belong to the same genus but since they infect archaea rather than bacteria are likely to be placed in a separate genus once their classification has been settled.
A dwarf group has been proposed on morphological and genomic grounds. This group includes the phages Aeromonas salmonicida phage 56, Vibrio cholerae phages 138 and CP-T1, Bdellovibrio phage φ1422 and Pectobacterium carotovorum phage ZF40. Their shared characteristics include an identical virion morphology, characterized by usually short contractile tails and all have genome sizes of approximately 45 kilobases. The gene order in the structural unit of the genome is in the order: terminase – portal – head – tail – base-plate – tail fibers.
Subfamily Teequatrovirinae 
- Genus T4-like viruses:
Subfamily Peduovirinae 
- Genus P2-like viruses; type species: Enterobacteria phage P2
- Genus Unassigned
- Genus SPO1-like viruses: type species: Bacillus phage SPO1
- Genus Twort-like viruses:
Species unassigned to a genus in this subfamily:
Subfamily Tevenvirinae 
- Genus T4likevirus
Genera not yet assigned to a subfamily 
- Genus Bcep781-like viruses
- Genus BcepMu-like viruses:
- Genus Felix O1-like viruses:
- Genus HAP1-like viruses:
- Genus I3-like viruses; type species: Mycobacterium phage I3
- Genus Mu-like viruses; type species: Enterobacteria phage Mu
- Genus P1-like viruses; type species: Enterobacteria phage P1
- Genus PB1-like viruses:
- Genus phiCD119-like viruses
- Genus PhiH-like viruses; type species: Halobacterium phage phiH
- Genus PhiKZ-like viruses; type species: Pseudomonas aeruginosa phage phiKZ
- Genus rV5-like viruses
- Genus Viunalikevirus
- Acinetobacter phage E14
- Acinetobacter phage phiAB8
- Dickeya phage LIMEstone1
- Escherichia phage CBA120
- Escherichia phage ECML-4
- Escherichia phage PhaxI
- Salmonella phage Det7
- Salmonella phage Vi1
- Salmonella phage SFP10
- Salmonella phage ΦSH19
- Serratia phage KSP90
- Shigella phage phiSboM-AG3
- Stenotrophomonas phage Smp14
Unassigned species 
- Genus Unassigned
- Acinetobacter phage E4
- Acinetobacter phage E5
- Aeromonas phage 1
- Aeromonas phage 25
- Aeromonas salomicida phage 31
- Aggregatibacter phage Aaphi23
- Bacillus phage G
- Bacillus phage PBS1
- Bacillus cereus phage Bace-11
- Bacillus megaterium phage MP13
- Bacillus subtilis killer virus defect particle
- Bacillus thuringiensis phage 03058-36
- Clostridium phage c-st
- Cronobacter sakazakii phage ES2
- Cronobacter sakazakii phage ESP2949-1
- Delftia phage phiW-14
- Escherichia phage phiEcoM-GJ1
- Gluconobacter virus Wer
- "Halocynthia" phage JM-2012
- Leptospira bacteriophage LE1
- Microcystis aeruginosa phage Ma-LMM01
- Natrialba magadii virus psiCh1
- Pseudomonas phage EL
- Ralstonia solanacearum phage RSL1
- Ralstonia solanacearum phage RSA1
- Rhodothermus phage RM378
- Sphingomonas phage PAU
- Streptococcus phage EJ-1
- Thermus phage YS40
- phage P-SSM2
- phage P-SSM4
- phage S-PM2
- phage Syn9
- Lavigne R, Darius P, Summer EJ, Seto D, Mahadevan P, Nilsson AS, Ackermann HW, Kropinski AM (2009) Classification of Myoviridae bacteriophages using protein sequence similarity. BMC Microbiol 9:224.
- Tang SL, Nuttall S, Dyall-Smith M (2004) Haloviruses HF1 and HF2: evidence for a recent and large recombination event. J Bacteriol 186(9):2810-2807
- Comeau AM, Tremblay D, Moineau S, Rattei T, Kushkina AI, Tovkach FI, Krisch HM, Ackermann HW (2012) Phage morphology recapitulates phylogeny: the comparative genomics of a new group of myoviruses. PLoS One 7(7):e40102.