Mamavirus

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Mamavirus
Virus classification OOjs UI icon edit-ltr.svg
(unranked): Virus
Realm: Varidnaviria
Kingdom: Bamfordvirae
Phylum: Nucleocytoviricota
Class: Megaviricetes
Order: Imitervirales
Family: Mimiviridae
Genus: Mimivirus
Species:
Mamavirus

Mamavirus is a large and complex virus in the Group I family Mimiviridae . [1] The virus is exceptionally large, and larger than many bacteria. Mamavirus and other mimiviridae belong to nucleocytoplasmic large DNA virus (NCLDVs) family. [2] Mamavirus can be compared to the similar complex virus mimivirus; mamavirus was so named because it is similar to but larger than mimivirus.

Contents

Discovery

Mamavirus was first reported in September 2008. Like mimivirus, mamavirus was isolated from an amoeba in a cooling tower. The mimiviridae were not discovered until recently because of their size; when filtered the mimiviridae stay with the bacteria which led scientists to believe they were also bacteria. Mimivirus was first isolated in 1992 when scientists were looking for the cause of a pneumonia outbreak in Bradford, UK. Due to its size it was named Bradfordcoccus and put in a freezer with scientists thinking it was a bacterium. [2] A decade later, Jean-Michel Claverie and Didier Raoult discovered “Bradfordcoccus” was no bacterium when they tried to digest the cell wall with no success. Deciding to take a different route they looked at it under an electron microscope. They were surprised to find that it looked like a giant iridovirus , which are icosahedral viruses that infect insects, fish, and frogs. Knowing this paved the way for the discovery of mamavirus because scientists knew to look for other giant viruses. [3]

It was originally isolated from Acanthamoeba polyphaga , but subsequent work has involved Acanthamoeba castellanii (Acanthamoeba castellanii mamavirus, ACMV). [4]

Structure and genome

Mamavirus, like other mimiviridae, is icosahedral with a core capsid and a peripheral fiber layer. It contains a linear double-stranded DNA genome which has a very high coding density that is characteristic of NCLDVs. The mimiviridae contain very similar genomes due to gene duplications, and a fair piece of the genome is associated with functions not previously found in a virus. [1]

Replication

Mamavirus possesses its own transcription machinery, and it packages transcription proteins in its particles. Transcription is believed to occur in the core particles. The core releases viral DNA and forms a cytoplasmic replication factory where DNA replication begins and transcription of late genes occurs. The replication factory forms around the viral core and expands until it occupies a large fraction of the amoeba cell volume. Later stages of the replication cycle involve partially assembled procapsids undergoing DNA packaging. [1]

Sputnik virophage

While the mimiviridae were a surprise themselves, mamavirus contained an even bigger surprise. While looking at mamavirus under the electron microscope, Raoult discovered a second, small virus closely associated with mamavirus which was named Sputnik virophage, a satellite virus. [5] Sputnik contains 21 genes and is tiny compared to mamavirus; however, it is quite powerful in its effects on mamavirus. Sputnik cannot replicate in acanthamoeba cells without a simultaneous infection by mamavirus (or mimivirus) so it infects the viral factory that mamavirus creates and hijacks it to replicate its own genome. [6] This causes mamavirus to produce fewer viruses that are often deformed and less effective; there is also evidence of a partial thickening of the capsid. The fact that Sputnik can do this suggests that it is a viral parasite, and thus, was named the first virophage. A virophage is similar to bacteriophage viruses, which infect and sicken bacteria, but virophages infect viruses. Sputnik contains a circular double-stranded DNA of 18,343 base pairs, and is icosahedral in shape. [7] Of the 21 genes it contains, eight encode proteins that have homologues. Of these eight, three are thought to be derived from mamavirus or mimivirus. [8] This indicates that Sputnik can participate in gene-transfer processes and mediate lateral gene transfer between giant viruses. [9]

Implications

Mamavirus has caused scientists to review the criteria of life; to start questioning whether viruses are alive, revive the debate about the origin of DNA viruses and their possible role in the emergence of the eukaryotic nucleus. [5]

See also

Related Research Articles

<i>Mimivirus</i> Genus of viruses

Mimivirus is a genus of giant viruses, in the family Mimiviridae. Amoeba serve as their natural hosts. This genus contains a single identified species named Acanthamoeba polyphaga mimivirus (APMV). It also refers to a group of phylogenetically related large viruses.

<span class="mw-page-title-main">Satellite (biology)</span> Subviral agent which depends on a helper virus for its replication

A satellite is a subviral agent that depends on the coinfection of a host cell with a helper virus for its replication. Satellites can be divided into two major classes: satellite viruses and satellite nucleic acids. Satellite viruses, which are most commonly associated with plants, are also found in mammals, arthropods, and bacteria. They encode structural proteins to enclose their genetic material, which are therefore distinct from the structural proteins of their helper viruses. Satellite nucleic acids, in contrast, do not encode their own structural proteins, but instead are encapsulated by proteins encoded by their helper viruses. The genomes of satellites range upward from 359 nucleotides in length for satellite tobacco ringspot virus RNA (STobRV).

<span class="mw-page-title-main">Mobilome</span>

The mobilome is the entire set of mobile genetic elements in a genome. Mobilomes are found in eukaryotes, prokaryotes, and viruses. The compositions of mobilomes differ among lineages of life, with transposable elements being the major mobile elements in eukaryotes, and plasmids and prophages being the major types in prokaryotes. Virophages contribute to the viral mobilome.

<span class="mw-page-title-main">Virophage</span> Viral parasites of giant viruses

Virophages are small, double-stranded DNA viral phages that require the co-infection of another virus. The co-infecting viruses are typically giant viruses. Virophages rely on the viral replication factory of the co-infecting giant virus for their own replication. One of the characteristics of virophages is that they have a parasitic relationship with the co-infecting virus. Their dependence upon the giant virus for replication often results in the deactivation of the giant viruses. The virophage may improve the recovery and survival of the host organism.

<span class="mw-page-title-main">Sputnik virophage</span> Subviral agent

Mimivirus-dependent virus Sputnik is a subviral agent that reproduces in amoeba cells that are already infected by a certain helper virus; Sputnik uses the helper virus's machinery for reproduction and inhibits replication of the helper virus. It is known as a virophage, in analogy to the term bacteriophage.

<i>Mimiviridae</i> Family of viruses

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 (NCLDV), also referred to as giant viruses.

Marseillevirus is a genus of viruses, in the family Marseilleviridae. There are two species in this genus. It is the prototype of a family of nucleocytoplasmic large DNA viruses (NCLDV) of eukaryotes. It was isolated from amoeba.

<i>Cafeteria roenbergensis virus</i> Species of virus

Cafeteria roenbergensis virus (CroV) is a giant virus that infects the marine bicosoecid flagellate Cafeteria roenbergensis, a member of the microzooplankton community.

A giant virus, sometimes referred to as a girus, is a very large virus, some of which are larger than typical bacteria. All known giant viruses belong to the phylum Nucleocytoviricota.

<i>Marseilleviridae</i> Family of viruses

Marseilleviridae is a family of viruses first named in 2012. The genomes of these viruses are double-stranded DNA. Amoeba are often hosts, but there is evidence that they are found in humans as well. The family contains one genus and four species, two of which are unassigned to a genus. It is a member of the nucleocytoplasmic large DNA viruses clade.

<i>Megavirus</i> Genus of viruses

Megavirus is a viral genus, phylogenetically related to Acanthamoeba polyphaga mimivirus (APMV). In colloquial speech, Megavirus chilense is more commonly referred to as just "Megavirus". Until the discovery of pandoraviruses in 2013, it had the largest capsid diameter of all known viruses, as well as the largest and most complex genome among all known viruses.

<i>Pandoravirus</i> Genus of giant virus possessing a large double-stranded DNA genome

Pandoravirus is a proposed genus of giant virus, first discovered in 2013. It is the third largest in physical size of any known viral genus, behind Pithovirus and Megaklothovirus. Pandoraviruses have double stranded DNA genomes, with the largest genome size of any known viral genus.

<i>Alphapithovirus</i> Genus of viruses

Alphapithovirus, is a genus of giant virus known from two species, Alphapithovirus sibericum, which infects amoebas, and Alphapithovirus massiliense. It is DNA-based and is a member of the nucleocytoplasmic large DNA viruses clade. It was discovered in 2014, when a viable specimen was found in a 30,000-year-old ice core harvested from permafrost in Siberia, Russia.

<span class="mw-page-title-main">Zamilon virophage</span> Virus type

Mimivirus-dependent virus Zamilon, or Zamilon, is a virophage, a group of small DNA viruses that infect protists and require a helper virus to replicate; they are a type of satellite virus. Discovered in 2013 in Tunisia, infecting Acanthamoeba polyphaga amoebae, Zamilon most closely resembles Sputnik, the first virophage to be discovered. The name is Arabic for "the neighbour". Its spherical particle is 50–60 nm in diameter, and contains a circular double-stranded DNA genome of around 17 kb, which is predicted to encode 20 polypeptides. A related strain, Zamilon 2, has been identified in North America.

<i>Faustovirus</i> Genus of viruses

Faustovirus is a genus of giant virus which infects amoebae associated with humans. The virus was first isolated in 2015 and shown to be around 0.2 micrometers in diameter with a double stranded DNA genome of 466 kilobases predicted to encode 451 proteins. Although classified as a nucleocytoplasmic large DNA virus (NCLDV), faustoviruses share less than a quarter of their genes with other NCLDVs; however, ~46% are homologous to bacterial genes and the remainder are orphan genes (ORFans). Specifically, the gene encoding the major capsid protein (MCP) of faustovirus is different than that of its most closely related giant virus, asfivirus, as well as other NCLDVs. In asfivirus, the gene encoding MCP is a single genomic fragment of ~2000 base pairs (bp), however, in faustovirus the MCP is encoded by 13 exons separated by 12 large introns. The exons have a mean length of 149 bp and the introns have a mean length of 1,273 bp. The presence of introns in faustovirus genes is highly unusual for viruses.

<i>Tupanvirus</i> Proposed genus of viruses

Tupanvirus is a genus of viruses first described in 2018. The genus is composed of two species of virus that are in the giant virus group. Researchers discovered the first isolate in 2012 from deep water sediment samples taken at 3,000 m depth off the coast of Brazil. The second isolate was collected from a soda lake in Southern Nhecolândia, Brazil in 2014. They are named after Tupã (Tupan), a Guaraní thunder god, and the places they were found. These are the first viruses reported to possess genes for amino-acyl tRNA synthetases for all 20 standard amino acids.

<span class="mw-page-title-main">Chrysochromulina ericina virus</span> Giant virus

Chrysochromulina ericina virus 01B, or simply Chrysochromulina ericina virus (CeV) is a giant virus in the family Mimiviridae infecting Haptolina ericina, a marine microalgae member of the Haptophyta. CeV is a dsDNA virus.

<i>Medusavirus</i> Type of virus

Medusavirus is a nucleocytoplasmic large DNA virus first isolated from a Japanese hot spring in 2019. It notably encodes all five types of histones — H1, H2A, H2B, H3, and H4 — which are involved in DNA packaging in eukaryotes, raising the possibility that they may have been involved in the origin of eukaryotes. The virus can harden amoebas of the species Acanthamoeba castellanii into stone-like cysts, but infection usually causes infected amoebas to burst open. The virus was named after Medusa, the monster in Greek mythology whose gaze turned people to stone.

<span class="mw-page-title-main">Marine viruses</span> Viruses found in marine environments

Marine viruses are defined by their habitat as viruses that are found in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Viruses are small infectious agents that can only replicate inside the living cells of a host organism, because they need the replication machinery of the host to do so. They can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

Nucleocytoviricota is a phylum of viruses. Members of the phylum are also known as the nucleocytoplasmic large DNA viruses (NCLDV), which serves as the basis of the name of the phylum with the suffix -viricota for virus phylum. These viruses are referred to as nucleocytoplasmic because they are often able to replicate in both the host's cell nucleus and cytoplasm.

References

  1. 1 2 3 Van Etten, James L.; Leslie C. Lane; David D. Dunigan (13 October 2010). "DNA Viruses: The Really Big Ones (Giruses)". Annual Review of Microbiology. 64. Annual Reviewof Microbiology: 83–99. doi:10.1146/annurev.micro.112408.134338. PMC   2936810 . PMID   20690825.
  2. 1 2 Claverie, Jean-Michel; Chantal Abergel (2009). "Mimivirus and its Virophage". Annual Review of Genetics. 43: 49–66. doi:10.1146/annurev-genet-102108-134255. PMID   19653859.
  3. ↑ Ehrenberg, Rachel (10 October 2009). "Enter the Virosphere: As evidence of the influence of viruses escalates, appreciation of these master manipulators grows". Science News. 176 (8): 22–25. doi:10.1002/scin.5591760820.
  4. ↑ Colson P, Yutin N, Shabalina SA, et al. (June 2011). "Viruses with more than 1000 genes: Mamavirus, a new Acanthamoeba castellanii mimivirus strain, and reannotation of mimivirus genes". Genome Biol Evol. 3: 737–42. doi:10.1093/gbe/evr048. PMC   3163472 . PMID   21705471.
  5. 1 2 Pearson, Helen (7 August 2008). "'Virophage' suggests viruses are alive". Nature. 454 (7205): 677. Bibcode:2008Natur.454..677P. doi:10.1038/454677a. PMID   18685665.
  6. ↑ La Scola, Bernard; Christelle Desnues; Isabelle Pagnier; Catherine Robert; Lina Barrassi; Ghislain Fournous; Michele Merchat; Marie Suzan-Monti; Patrick Forterre; Eugene Koonin; Didier Raoult (4 September 2008). "The virophage as a unique parasite of the giant mimivirus" (PDF). Nature. pp. 100–105. Archived from the original (PDF) on 22 March 2012. Retrieved 11 April 2011.
  7. ↑ Desnues, C; D. Raoult (15 June 2010). "Inside the Lifestyle of the Virophage". Intervirology. 53 (5): 293–303. doi: 10.1159/000312914 . PMID   20551681.
  8. ↑ Sun, Siyang; Bernard La Scola; Valorie D. Bownam; Christopher M. Ryan; Julian P. Whitelegge; Didier Raoult; Michael G. Rossmann (January 2010). "Structural Studies of the Sputnik Virophage". Journal of Virology. 84 (2): 894–897. doi:10.1128/JVI.01957-09. PMC   2798384 . PMID   19889775.
  9. ↑ Smallridge, Rachel (2008). "Virology: A Virus gets a Virus". Nature Reviews Microbiology. 6 (10). Nature Reviews: 714. doi: 10.1038/nrmicro2002 . S2CID   37328706.
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