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== History == |
== History == |
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The first giant virus, then named BV-PW1, was isolated and described in 1995,<ref>{{Cite journal|last1=Garza|first1=D. Randy|last2=Suttle|first2=Curtis A.|date=1995-12-31|title=Large double-stranded DNA viruses which cause the lysis of a marine heterotrophic nanoflagellate (Bodo sp) occur in natural marine viral communities|url=https://www.int-res.com/abstracts/ame/v09/n3/p203-210//|journal=Aquatic Microbial Ecology|volume=9|issue=3|pages=133–144|doi=10.3354/ame009203}}</ref> but was not recognized as such until its sequenced genome was released as [[Cafeteria roenbergensis virus]] (CroV) in 2010.<ref>{{cite journal |pages=19508–13 |doi=10.1073/pnas.1007615107 |pmc=2984142 |title=Giant virus with a remarkable complement of genes infects marine zooplankton |year=2010 |last1=Fischer |first1=M. G. |last2=Allen |first2=M. J. |last3=Wilson |first3=W. H. |last4=Suttle |first4=C. A. |journal=Proceedings of the National Academy of Sciences |volume=107 |issue=45 |pmid=20974979|bibcode=2010PNAS..10719508F |url=http://pubman.mpdl.mpg.de/pubman/item/escidoc:2272841/component/escidoc:2272838/PNAS_107_2010_19508.pdf |doi-access=free }}</ref> Subsequently, the Giant Virus [[mimivirus|''Acanthamoeba polyphaga'' Mimivirus]] was characterized<ref>{{cite journal |vauthors=La Scola B, Audic S, Robert C, Jungang L, de Lamballerie X, Drancourt M, Birtles R, Claverie JM, Raoult D |title=A giant virus in amoebae |journal=Science |volume=299 |issue=5615 |pages=2033|year=2003|pmid=12663918|doi=10.1126/science.1081867|s2cid=39606235}}</ref> (which had been mistaken as a bacterium in 1993),<ref>{{Cite web|date=2017-02-06|title=Giant Viruses|url=https://www.americanscientist.org/article/giant-viruses|access-date=2021-09-02|website=American Scientist|language=en}}</ref> and then sequenced.<ref name="Raoult2004">{{cite journal | vauthors = Raoult D, Audic S, Robert C, Abergel C, Renesto P, Ogata H, La Scola B, Suzan M, Claverie JM | title = The 1.2-megabase genome sequence of Mimivirus | journal = Science | volume = 306 | issue = 5700 | pages = 1344–50 | date = November 2004 | pmid = 15486256 | doi = 10.1126/science.1101485 | bibcode = 2004Sci...306.1344R | s2cid = 84298461 }}</ref> The term "girus" was coined to refer to the group in 2006.<ref name="claverie_2006">{{cite journal |last1=Claverie |first1=Jean-Michel |last2=Ogata |first2=Hiroyuki |last3=Audic |first3=Stéphane |last4=Abergel |first4=Chantal |last5=Suhre |first5=Karsten |last6=Fournier |first6=Pierre-Edouard |title=Mimivirus and the emerging concept of "giant" virus |journal=Virus Research |date=April 2006 |volume=117 |issue=1 |pages=133–144 |doi=10.1016/j.virusres.2006.01.008|pmid=16469402 |url=https://arxiv.org/ftp/q-bio/papers/0506/0506007.pdf|arxiv=q-bio/0506007 |s2cid=8791457 }}</ref> |
The first giant viruses to be described were chloroviruses of the family Phycodnaviridae. These were discovered in 1981 by Russel H. Meints, James L. Van Etten, Daniel Kuczmarski, Kit Lee, and Barbara Ang. The first chlorovirus was initially called HVCV (Hydra viridis Chlorella virus) since it was first found to infect Chlorella-like algae.<ref>{{cite journal|last1=Meints|first1=Russel H.|last2=Van Etten|first2=James L.|last3=Kuczmarski|first3=Daniel|last4=Lee|first4=Kit|last5=Ang|first5=Barbara|title=Viral infection of the symbiotic chlorella-like alga present in Hydra viridis|journal=Virology|date=September 1981|volume=113|issue=2|pages=698–703|doi=10.1016/0042-6822(81)90198-7|pmid=18635088}}</ref><ref>{{cite journal|last1=Hoshina|first1=Ryo|last2=Shimizu|first2=Mayumi|last3=Makino|first3=Yoichi|last4=Haruyama|first4=Yoshihiro|last5=Ueda|first5=Shin-ichiro|last6=Kato|first6=Yutaka|last7=Kasahara|first7=Masahiro|last8=Ono|first8=Bun-ichiro|last9=Imamura|first9=Nobutaka|title=Isolation and characterization of a virus (CvV-BW1) that infects symbiotic algae of Paramecium bursaria in Lake Biwa, Japan|journal=Virology Journal|date=13 September 2010|volume=7|pages=222|doi=10.1186/1743-422X-7-222|pmid=20831832|pmc=2949830|language=en|issn=1743-422X}}</ref> |
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Other giant viruses that infected marine flagellates were described later. The first of these, then named BV-PW1, was isolated and described in 1995,<ref>{{Cite journal|last1=Garza|first1=D. Randy|last2=Suttle|first2=Curtis A.|date=1995-12-31|title=Large double-stranded DNA viruses which cause the lysis of a marine heterotrophic nanoflagellate (Bodo sp) occur in natural marine viral communities|url=https://www.int-res.com/abstracts/ame/v09/n3/p203-210//|journal=Aquatic Microbial Ecology|volume=9|issue=3|pages=133–144|doi=10.3354/ame009203}}</ref> but was not recognized as such until its sequenced genome was released as [[Cafeteria roenbergensis virus]] (CroV) in 2010.<ref>{{cite journal |pages=19508–13 |doi=10.1073/pnas.1007615107 |pmc=2984142 |title=Giant virus with a remarkable complement of genes infects marine zooplankton |year=2010 |last1=Fischer |first1=M. G. |last2=Allen |first2=M. J. |last3=Wilson |first3=W. H. |last4=Suttle |first4=C. A. |journal=Proceedings of the National Academy of Sciences |volume=107 |issue=45 |pmid=20974979|bibcode=2010PNAS..10719508F |url=http://pubman.mpdl.mpg.de/pubman/item/escidoc:2272841/component/escidoc:2272838/PNAS_107_2010_19508.pdf |doi-access=free }}</ref> Subsequently, the Giant Virus [[mimivirus|''Acanthamoeba polyphaga'' Mimivirus]] was characterized<ref>{{cite journal |vauthors=La Scola B, Audic S, Robert C, Jungang L, de Lamballerie X, Drancourt M, Birtles R, Claverie JM, Raoult D |title=A giant virus in amoebae |journal=Science |volume=299 |issue=5615 |pages=2033|year=2003|pmid=12663918|doi=10.1126/science.1081867|s2cid=39606235}}</ref> (which had been mistaken as a bacterium in 1993),<ref>{{Cite web|date=2017-02-06|title=Giant Viruses|url=https://www.americanscientist.org/article/giant-viruses|access-date=2021-09-02|website=American Scientist|language=en}}</ref> and then sequenced.<ref name="Raoult2004">{{cite journal | vauthors = Raoult D, Audic S, Robert C, Abergel C, Renesto P, Ogata H, La Scola B, Suzan M, Claverie JM | title = The 1.2-megabase genome sequence of Mimivirus | journal = Science | volume = 306 | issue = 5700 | pages = 1344–50 | date = November 2004 | pmid = 15486256 | doi = 10.1126/science.1101485 | bibcode = 2004Sci...306.1344R | s2cid = 84298461 }}</ref> The term "girus" was coined to refer to the group in 2006.<ref name="claverie_2006">{{cite journal |last1=Claverie |first1=Jean-Michel |last2=Ogata |first2=Hiroyuki |last3=Audic |first3=Stéphane |last4=Abergel |first4=Chantal |last5=Suhre |first5=Karsten |last6=Fournier |first6=Pierre-Edouard |title=Mimivirus and the emerging concept of "giant" virus |journal=Virus Research |date=April 2006 |volume=117 |issue=1 |pages=133–144 |doi=10.1016/j.virusres.2006.01.008|pmid=16469402 |url=https://arxiv.org/ftp/q-bio/papers/0506/0506007.pdf|arxiv=q-bio/0506007 |s2cid=8791457 }}</ref> |
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==Genetics and evolution== |
==Genetics and evolution== |
Megaviricetes | |
---|---|
Mimivirus | |
Virus classification | |
(unranked): | Virus |
Realm: | Varidnaviria |
Kingdom: | Bamfordvirae |
Phylum: | Nucleocytoviricota |
Class: | Megaviricetes |
Agiant virus, sometimes referred to as a girus, is a very large virus, some of which are larger than typical bacteria.[1][2] All known giant viruses belong to the phylum Nucleocytoviricota.[3]
While the exact criteria as defined in the scientific literature vary, giant viruses are generally described as viruses having large, pseudo-icosahedral capsids (200 to 400 nanometers)[4] that may be surrounded by a thick (approximately 100 nm) layer of filamentous protein fibers. The viruses' large, double-stranded DNA genomes (300 to 1000 kilobasepairs or larger) encode a large contingent of genes (of the order of 1000 genes).[3][5] While few giant viruses have been characterized in detail, the most notable examples are the phylogenetically related mimivirus and megavirus—both belonging to the Mimiviridae (aka Megaviridae) family, due to their having the largest capsid diameters of all known viruses.[3][5]Giant viruses from the deep ocean, terrestrial sources, and human patients contain genes encoding cytochrome P450 (CYP; P450) enzymes. The origin of these P450 genes in giant viruses remains unknown but may have been acquired from an ancient host.[6]
The genomes of many giant viruses encode many unusual genes that are not found in other viruses, including genes involved in glycolysis and the TCA cycle[7], fermentation[8], and the cytoskeleton[9][10][11].
The first giant viruses to be described were chloroviruses of the family Phycodnaviridae. These were discovered in 1981 by Russel H. Meints, James L. Van Etten, Daniel Kuczmarski, Kit Lee, and Barbara Ang. The first chlorovirus was initially called HVCV (Hydra viridis Chlorella virus) since it was first found to infect Chlorella-like algae.[12][13]
Other giant viruses that infected marine flagellates were described later. The first of these, then named BV-PW1, was isolated and described in 1995,[14] but was not recognized as such until its sequenced genome was released as Cafeteria roenbergensis virus (CroV) in 2010.[15] Subsequently, the Giant Virus Acanthamoeba polyphaga Mimivirus was characterized[16] (which had been mistaken as a bacterium in 1993),[17] and then sequenced.[18] The term "girus" was coined to refer to the group in 2006.[19]
The genomes of giant viruses are the largest known for viruses, and contain genes that encode for important elements of translation machinery, a characteristic that had previously been believed to be indicative of cellular organisms. These genes include multiple genes encoding a number of aminoacyl tRNA synthetases, enzymes that catalyze the esterification of specific amino acids or their precursors to their corresponding cognate tRNAs to form an aminoacyl tRNA that is then used during translation.[5] The presence of four aminoacyl tRNA synthetase encoding genes in mimivirus and mamavirus genomes, both species within the Mimiviridae family, as well as the discovery of seven aminoacyl tRNA synthetase genes, including the four genes present in Mimiviridae, in the megavirus genome provide evidence for a possible scenario in which these large DNA viruses evolved from a shared ancestral cellular genome by means of genome reduction.[5]
Their discovery and subsequent characterization has triggered some debate concerning the evolutionary origins of giant viruses. The two main hypotheses for their origin are that either they evolved from small viruses, picking up DNA from host organisms, or that they evolved from very complicated organisms into the current form which is not self-sufficient for reproduction.[20] What sort of complicated organism giant viruses might have diverged from is also a topic of debate. One proposal is that the origin point actually represents a fourth domain of life,[5] but this has been largely discounted.[21][22][23]
Giant virus name | Genome Length | Genes | Capsid diameter (nm) | Hair cover | Genbank # |
---|---|---|---|---|---|
Bodo saltans virus[24] | 1,385,869 | 1227 proteins (predicted) | ~300 | yes (~40 nm) | MF782455 |
Megavirus chilensis[25] | 1,259,197 | 1120 proteins (predicted) | 440 | yes (75 nm) | JN258408 |
Mamavirus[26] | 1,191,693 | 1023 proteins (predicted) | 500 | yes (120 nm) | JF801956 |
Mimivirus[18][27] | 1,181,549 | 979 proteins 39 non-coding | 500 | yes (120 nm) | NC_014649 |
M4[28] (Mimivirus "bald" variant) | 981,813 | 756 proteins (predicted) | 390 | No | JN036606 |
Tupanvirus[29] | 1,500,000 | 1276–1425 proteins | ≥450+550[30] | KY523104 MF405918[31] | |
Cafeteria roenbergensis virus[32] | 617,453 (730 kb) | 544 proteins (predicted) | 300 | No | NC_014637 |
The whole list is in the Giant Virus Toplist created by the Giant Virus Finder software.[33]
Giant virus name | Aminoacyl-tRNA synthetase | Octocoral-like 1MutS | 2Stargate[34] | Known virophage[35] | Cytoplasmic virion factory | Host |
---|---|---|---|---|---|---|
Megavirus chilensis | 7 (Tyr, Arg, Met, Cys, Trp, Asn, Ile) | yes | yes | no | yes | Acanthamoeba (Unikonta, Amoebozoa) |
Mamavirus | 4 (Tyr, Arg, Met, Cys) | yes | yes | yes | yes | Acanthamoeba (Unikonta, Amoebozoa) |
Mimivirus | 4 (Tyr, Arg, Met, Cys) | yes | yes | yes | yes | Acanthamoeba (Unikonta, Amoebozoa) |
M4 (Mimivirus "bald" variant) | 3 (Met, Cys, Arg) | yes | yes | Resistant | yes | Acanthamoeba (Unikonta, Amoebozoa) |
Cafeteria roenbergensis virus | 1 (Ile) | yes | no | yes | yes | Phagotrophic protozoan (Heterokonta, Stramenopiles) |
1Mutator S (MutS) and its homologs are a family of DNA mismatch repair proteins involved in the mismatch repair system that acts to correct point mutations or small insertion/deletion loops produced during DNA replication, increasing the fidelity of replication. 2A stargate is a five-pronged star structure present on the viral capsid forming the portal through which the internal core of the particle is delivered to the host's cytoplasm.
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Self-replicating organic structures
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Cellular life |
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Subviral agents |
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Nucleic acid self-replication |
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Endosymbiosis |
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Abiogenesis |
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See also |
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