Mimiviridae is the sole recognized member of order Imitervirales. Phycodnaviridae and Pandoraviridae of Algavirales are sister groups of Mimiviridae in many phylogenetic analyses.[5]
History
The first member of this family, Mimivirus, was discovered in 2003,[6] and the first complete genome sequence was published in 2004.[7] However, the mimivirus Cafeteria roenbergensis virus[8] was isolated and partially characterized in 1995,[9] although the host was misidentified at the time, and the virus was designated BV-PW1.[8]
Tupanvirus strains have been discussed to comprise a sister group of mimiviruses.[4]
Furthermore, it has been proposed either to extend Mimiviridae by an additional tentative group III (subfamily Mesomimivirinae) or to classify this group as a sister family Mesomimiviridae instead,[19] comprising legacy OLPG (Organic Lake Phycodna Group). This extension (or sister family) 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.[3][23][24][25][26][17]
With recognition of new order Imitervirales by the ICTV in 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 (or at least its main clade) may be referred to as a sister family Mesomimiviridae.[19]
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[27][28] Unassigned members include Aureococcus anophagefferens virus (AaV), CpV-BQ2 and Terra2.[citation needed]
Structure
[18] 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.[1]
Genus
Structure
Symmetry
Genomic arrangement
Genomic segmentation
Mimivirus
Icosahedral
T=972-1141 or T=1200 (H=19 +/- 1, K=19 +/- 1)
Linear
Monopartite
Klosneuvirus
Icosahedral
Cafeteriavirus
Icosahedral
T=499
Linear
Monopartite
Tupanvirus
Tailed
Life cycle
Replication follows the DNA strand displacement model. DNA-templated transcription is the method of transcription. Amoeba serve as the natural host.[1]
Genus
Host details
Tissue tropism
Entry details
Release details
Replication site
Assembly site
Transmission
Mimivirus
Amoeba
None
Unknown
Unknown
Unknown
Unknown
Passive diffusion
Klosneuvirus
microzooplankton
None
Unknown
Unknown
Unknown
Cytoplasm
Passive diffusion
Cafeteriavirus
microzooplankton
None
Unknown
Unknown
Unknown
Cytoplasm
Passive diffusion
Molecular biology
Three putative DNA base excision repair enzymes were characterized from Mimivirus.[29] The base excision repair (BER) pathway was experimentally reconstituted using the purified recombinant proteins uracil-DNA glycosylase (mvUDG), AP endonuclease (mvAPE), and DNA polymerase X protein (mvPolX).[29] When reconstituted in vitro mvUDG, mvAPE and mvPolX function cohesively to repair uracil-containing DNA predominantly by long patch base excision repair, and thus these processes likely participate in the BER pathway early in the Mimivirus life cycle.[29]
Clinical
Mimiviruses have been associated with pneumonia but their significance is currently unknown.[30] The only virus of this family isolated from a human to date is LBA 111.[31] At the Pasteur Institute of Iran (Tehran), researchers identified mimivirus DNA in bronchoalveolar lavage (BAL) and sputum samples of a child patient, utilizing real-time PCR (2018). Analysis reported 99% homology of LBA111, lineage C of the Megavirus chilensis.[32] With only a few reported cases previous to this finding, the legitimacy of the mimivirus as an emerging infectious disease in humans remains controversial.[33][34]
^Yoosuf N, Pagnier I, Fournous G, Robert C, La Scola B, Raoult D, Colson P (April 2014). "Complete genome sequence of Courdo11 virus, a member of the family Mimiviridae". Virus Genes. 48 (2): 218–23. doi:10.1007/s11262-013-1016-x. PMID24293219. S2CID12038772.