Genome organization within this group varies considerably. Some have circular genomes (Baculoviridae,Papovaviridae and Polydnaviridae) while others have linear genomes (Adenoviridae, Herpesviridae and some phages). Some families have circularly permuted linear genomes (phage T4 and some Iridoviridae). Others have linear genomes with covalently closed ends (Poxviridae and Phycodnaviridae).

A virus infecting archaea was first described in 1974. Several others have been described since: most have head-tail morphologies and linear double-stranded DNA genomes. Other morphologies have also been described: spindle shaped, rod shaped, filamentous, icosahedral and spherical. Additional morphological types may exist.

Orders within this group are defined on the basis of morphology rather than DNA sequence similarity. It is thought that morphology is more conserved in this group than sequence similarity or gene order which is extremely variable. Three orders and 31 families are currently recognised. A fourth order - Megavirales - for the nucleocytoplasmic large DNA viruses has been proposed.^[1] Four genera are recognised that have not yet been assigned a family. The species Sulfolobus turreted icosahedral virus is so unlike any previously described virus that it will almost certainly be placed in a new family on the next revision of viral families.

Fifteen families are enveloped. These include all three families in the order Herpesvirales and the following families: Ascoviridae, Ampullaviridae, Asfarviridae, Baculoviridae, Fuselloviridae,Globuloviridae, Guttaviridae, Hytrosaviridae, Iridoviridae, Lipothrixviridae, Nimaviridae and Poxviridae.

Bacteriophages (viruses infecting bacteria) belonging to the families Tectiviridae and Corticoviridae have a lipid bilayer membrane inside the icosahedral protein capsid and the membrane surrounds the genome. The crenarchaeal virus Sulfolobus turreted icosahedral virus has a similar structure.

The genomes in this group vary considerably from ~20 kilobases to over 1.2 megabases in length.

[edit]Host range

Species of the order Caudovirales and of the families Corticoviridae and Tectiviridae infect bacteria.

Species of the order Ligamenvirales and the families Ampullaviridae, Bicaudaviridae, Clavaviridae, Fuselloviridae, Globuloviridae and Guttaviridae infect hyperthermophilic archaea species of theCrenarchaeota.

Species of the order Herpesvirales and of the families Adenoviridae, Asfarviridae, Iridoviridae, Papillomaviridae, Polyomaviridae and Poxviridae infect vertebrates.

Species of the families Ascovirus, Baculovirus, Hytrosaviridae, Iridoviridae and Polydnaviruses and of the genus Nudivirus infect insects.

Species of the family Mimiviridae and the species Marseillevirus, Megavirus, Mavirus virophage and Sputnik virophage infect protozoa.

Species of the family Nimaviridae infect crustaceans.

Species of the family Phycodnaviridae and the species Organic Lake virophage infect algae. These are the only known dsDNA viruses that infect plants.

Species of the family Plasmaviridae infect species of the class Mollicutes.

Species of the genus Dinodnavirus infect dinoflagellates. These are the only known viruses that infect dinoflagellates.

Species of the genus Rhizidiovirus infect stramenopiles. These are the only known dsDNA viruses that infect stramenopiles.

Species of the genus Salterprovirus infect halophilic archaea species of the Euryarchaeota.

[edit]Taxonomy

• Order Caudovirales
  • Family Myoviridae - includes Enterobacteria phage T4
  • Family Podoviridae - includes Enterobacteria phage T7
  • Family Siphoviridae - includes Enterobacteria phage λ

• Order Herpesvirales
  • Family Alloherpesviridae
  • Family Herpesviridae - includes human herpesviruses, Varicella Zoster virus
  • Family Malacoherpesviridae

• Order Ligamenvirales
  • Family Lipothrixviridae
  • Family Rudiviridae

• Unassigned families
  • Family Adenoviridae - includes viruses which cause human adenovirus infection
  • Family Ampullaviridae
  • Family Ascoviridae
  • Family Asfarviridae - includes African swine fever virus
  • Family Baculoviridae
  • Family Bicaudaviridae
  • Family Clavaviridae
  • Family Corticoviridae
  • Family Fuselloviridae
  • Family Globuloviridae
  • Family Guttaviridae
  • Family Hytrosaviridae
  • Family Iridoviridae
  • Family Mimiviridae
  • Family Nimaviridae
  • Family Papillomaviridae
  • Family Phycodnaviridae
  • Family Plasmaviridae
  • Family Polydnaviruses
  • Family Polyomaviridae - includes Simian virus 40, JC virus, BK virus
  • Family Poxviridae - includes Cowpox virus, smallpox
  • Family Tectiviridae

• Unassigned genera
  • Dinodnavirus
  • Nudivirus
  • Salterprovirus
  • Rhizidiovirus

• Unassigned species
  • Abalone shriveling syndrome-associated virus
  • Bandicoot papillomatosis carcinomatosis virus
  • KIs-V
  • Haloarcula hispanica pleomorphic virus 1
  • Haloarcula hispanica SH1 virus
  • Marseillevirus
  • Mavirus virophage
  • Megavirus
  • Organic Lake virophage
  • Sputnik virophage
  • Sputnik virophage 2
  • Sulfolobus turreted icosahedral virus
  • Thermus aquaticus virus IN93
  • Thermus thermophilus virus P23-77

[edit]Notes

Haloarcula hispanica SH1 virus, Thermus aquaticus virus IN93 and Thermus thermophilus virus P23-77 share a number of unique structural features.^[2] It seems likely that they will be placed into a new genus or family in the next revision of the taxonomy of this group.

A group known as the pleolipoviruses, although having a similar genome organisation, differ in having either single or double stranded DNA genomes.^[3] This group does not fit into the current classification system.

This group includes the following viruses:

• Haloarcula hispanica pleomorphic virus 1
• Halogeometricum pleomorphic virus 1
• Halorubrum pleomorphic virus 1
• Halorubrum pleomorphic virus 2
• Halorubrum pleomorphic virus 3
• Halorubrum pleomorphic virus 6

[edit]