Myoviridae

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Myoviridae
Structural overview of the T4 phage
Virus classification
Group: Group I (dsDNA)
Order: Caudovirales
Family: Myoviridae
Genera

EL-like viruses
I3-like viruses
Mu-like viruses
P1-like viruses
P2-like viruses
PhiH-like viruses
PhiKZ-like viruses
rV5-like viruses
SPO1-like viruses
T4-like viruses
Vi01-like viruses
Viunalikevirus

The Myoviridae is a family of bacteriophages. It has been divided into four subfamiles and eleven genera.[1] Many species have not yet been assigned either a genus or a family. There are at least 130 species in this family.

Contents

Virology [edit]

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.

5-Hydroxymethylcytosine may be present in the genome (instead of thymidine).

Life cycle [edit]

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.

Although Myoviruses are in general lytic, lacking the genes required to become lysogenic, a number of lysogenic species are known.

Subdivisions [edit]

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.[2]

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.[3] 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.

Taxonomy [edit]

Subfamily Teequatrovirinae [edit]

  • Genus T4-like viruses:

Subfamily Peduovirinae [edit]

Subfamily Spounavirinae [edit]

Species unassigned to a genus in this subfamily:

Subfamily Tevenvirinae [edit]

Genera not yet assigned to a subfamily [edit]

Unassigned species [edit]

References [edit]

  1. ^ 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.
  2. ^ 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
  3. ^ 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.

External links [edit]
DNA
RNA
RT
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