Mimiviridae


Mimiviridae is a family of viruses. Amoeba and other protists serve as natural hosts. The family is divided in up to 4 subfamilies. Viruses in this family belong to the nucleocytoplasmic large DNA virus clade, also referred to as giant viruses.
Mimiviridae is the sole recognized member of order Imitervirales. Phycodnaviridae and Pandoraviridae of Algavirales are sister groups of Mimiviridae in many phylogenetic analyses.

History

The first member of this family, Mimivirus, was discovered in 2003, and the first complete genome sequence was published in 2004. However, the mimivirus Cafeteria roenbergensis virus was isolated and partially characterized in 1995, although the host was misidentified at the time, and the virus was designated BV-PW1.

Taxonomy

Group: dsDNA
Family Mimiviridae is currently divided into three subfamilies.
Furthermore, it has been proposed either to extend Mimiviridae by an additional tentative group III or to classify this group as a sister family Mesomimiviridae instead, comprising legacy OLPG. This extenion may consist of the following:
This group seems to be closely related to Mimiviridae rather than to Phycodnaviridae and therefore is sometimes referred to as a further subfamily candidate Mesomimivirinae. Sometimes the extended family Mimiviridae is referred to as Megaviridae although this has not been recognized by ICTV; alternatively the extended group may be referred to just as Mimiviridae.
With recognition of new order Imitervirales by the ICTV im march 2020 there is no longer need to extend the Mimiviridae family to comprise a group of viruses of the observed high diversity. Instead, the extension may be referred to as a sister family Mesomimiviridae.
Although only a couple of members of this order have been described in detail it seems likely there are many more awaiting description and assignment Unassigned members include Aureococcus anophagefferens virus, CpV-BQ2 and Terra2.

Structure

Viruses in Mimiviridae have icosahedral and round geometries, with between T=972 and T=1141, or T=1200 symmetry. The diameter is around 400 nm, with a length of 125 nm. Genomes are linear and non-segmented, around 1200kb in length. The genome has 911 open reading frames.
GenusStructureSymmetryGenomic arrangementGenomic segmentation
MimivirusIcosahedralT=972-1141 or T=1200 LinearMonopartite
KlosneuvirusIcosahedral
CafeteriavirusIcosahedralT=499LinearMonopartite
TupanvirusTailed

Life cycle

Replication follows the DNA strand displacement model. DNA-templated transcription is the method of transcription. Amoeba serve as the natural host.
GenusHost detailsTissue tropismEntry detailsRelease detailsReplication siteAssembly siteTransmission
MimivirusAmoeba-UnknownUnknownUnknownUnknownPassive diffusion
Klosneuvirusmicrozooplankton-UnknownUnknownUnknownCytoplasmPassive diffusion
Cafeteriavirusmicrozooplankton-UnknownUnknownUnknownCytoplasmPassive diffusion

Molecular biology

Within the genome of Lentille virus integrated genome of a virophage and a transpoviron—a mobile genetic element—have been reported. Transpovirons are linear DNA elements of about 7 kilobases that encompass six to eight protein coding genes, two of which are homologous to virophage genes. Broad spectrum of mimiviridae virophage allows its isolation using a mimivirus reporter.

Clinical

Mimiviruses have been associated with pneumonia but their significance if any is currently unknown. The only virus of this family isolated from a human to date is LBA 111. Mimivirus has also been implicated in rheumatoid arthritis.