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m v2.04b - Bot T20 CW#61 - Fix errors for CW project (Reference before punctuation)
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i added more info on giant viruses and explained about how they hunt and what hunts them.
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A '''giant virus''', sometimes referred to as a '''girus''', is a very large [[virus]], some of which are larger than typical bacteria.<ref>{{cite journal|last=Reynolds |first=Kelly A. | name-list-style = vanc |title=Mysterious Microbe in Water Challenges the Very Definition of a Virus |journal=Water Conditioning & Purification |year=2010 |url=http://www.wcponline.com/pdf/June_OnTap.pdf |url-status=dead |archive-url=https://web.archive.org/web/20140319025858/http://www.wcponline.com/pdf/June_OnTap.pdf |archive-date=2014-03-19 }}</ref><ref>{{cite journal | vauthors = Ogata H, Toyoda K, Tomaru Y, Nakayama N, Shirai Y, Claverie JM, Nagasaki K | title = Remarkable sequence similarity between the dinoflagellate-infecting marine girus and the terrestrial pathogen African swine fever virus | journal = Virology Journal | volume = 6 | issue = 178 | pages = 178 | date = October 2009 | pmid = 19860921 | pmc = 2777158 | doi = 10.1186/1743-422X-6-178 }}</ref> They have extremely large [[genomes]] compared to other viruses and contain many unique genes not found in life forms |
A '''giant virus''', sometimes referred to as a '''girus''', is a very large [[virus]], some of which are larger than typical bacteria.<ref>{{cite journal|last=Reynolds |first=Kelly A. | name-list-style = vanc |title=Mysterious Microbe in Water Challenges the Very Definition of a Virus |journal=Water Conditioning & Purification |year=2010 |url=http://www.wcponline.com/pdf/June_OnTap.pdf |url-status=dead |archive-url=https://web.archive.org/web/20140319025858/http://www.wcponline.com/pdf/June_OnTap.pdf |archive-date=2014-03-19 }}</ref><ref>{{cite journal | vauthors = Ogata H, Toyoda K, Tomaru Y, Nakayama N, Shirai Y, Claverie JM, Nagasaki K | title = Remarkable sequence similarity between the dinoflagellate-infecting marine girus and the terrestrial pathogen African swine fever virus | journal = Virology Journal | volume = 6 | issue = 178 | pages = 178 | date = October 2009 | pmid = 19860921 | pmc = 2777158 | doi = 10.1186/1743-422X-6-178 }}</ref> They have extremely large [[genomes]] compared to other viruses and contain many unique genes not found in life forms. All known giant viruses belong to the phylum ''[[Nucleocytoviricota]]''.<ref name=AmSci-099-4>{{cite journal |journal=American Scientist |title=Giant Viruses |first=James L. |last=Van Etten | name-list-style = vanc |date=July–August 2011 |volume=99 |issue=4 |pages=304–311 |doi=10.1511/2011.91.304 |url=http://www.americanscientist.org/issues/feature/2011/4/giant-viruses | archive-url = https://web.archive.org/web/20110621223431/http://www.americanscientist.org/issues/feature/2011/4/giant-viruses|archive-date=2011-06-11}}</ref> |
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==Description== |
==Description== |
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While the exact criteria as defined in the scientific literature vary, giant viruses are generally described as viruses having large, pseudo-[[Capsid#Icosahedral|icosahedral capsids]] (200 to 400 nanometers)<ref>{{cite journal | vauthors = Xiao C, Fischer MG, Bolotaulo DM, Ulloa-Rondeau N, Avila GA, Suttle CA | title = Cryo-EM reconstruction of the Cafeteria roenbergensis virus capsid suggests novel assembly pathway for giant viruses | journal = Scientific Reports | volume = 7 | issue = 5484 | date = 14 July 2017 | page = 5484 | pmid = 28710447 | pmc = 5511168 | doi = 10.1038/s41598-017-05824-w | bibcode = 2017NatSR...7.5484X }}</ref> 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).<ref name=AmSci-099-4/><ref name=Comm-005-1/> 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]]'' |
While the exact criteria as defined in the scientific literature vary, giant viruses are generally described as viruses having large, pseudo-[[Capsid#Icosahedral|icosahedral capsids]] (200 to 400 nanometers)<ref>{{cite journal | vauthors = Xiao C, Fischer MG, Bolotaulo DM, Ulloa-Rondeau N, Avila GA, Suttle CA | title = Cryo-EM reconstruction of the Cafeteria roenbergensis virus capsid suggests novel assembly pathway for giant viruses | journal = Scientific Reports | volume = 7 | issue = 5484 | date = 14 July 2017 | page = 5484 | pmid = 28710447 | pmc = 5511168 | doi = 10.1038/s41598-017-05824-w | bibcode = 2017NatSR...7.5484X }}</ref> 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).<ref name=AmSci-099-4/><ref name=Comm-005-1/> 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.<ref name=AmSci-099-4/><ref name=Comm-005-1>{{cite journal | vauthors = Legendre M, Arslan D, Abergel C, Claverie JM | title = Genomics of Megavirus and the elusive fourth domain of Life | journal = Communicative & Integrative Biology | volume = 5 | issue = 1 | pages = 102–6 | date = January 2012 | pmid = 22482024 | pmc = 3291303 | doi = 10.4161/cib.18624 }}</ref>Giant viruses from the deep ocean, terrestrial sources, and human patients contain genes encoding [[Cytochrome P450|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.<ref>{{cite journal|display-authors=6|vauthors=Lamb DC, Follmer AH, Goldstone JV, Nelson DR, Warrilow AG, Price CL, True MY, Kelly SL, Poulos TL, Stegeman JJ|date=June 2019|title=On the occurrence of cytochrome P450 in viruses|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=116|issue=25|pages=12343–12352|doi=10.1073/pnas.1901080116|pmc=6589655|pmid=31167942|doi-access=free}}</ref> |
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=== Confusing Genes === |
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[[File:CroV TEM.jpg|thumb|Cryo-EM images of the giant viruses [[CroV]] and [[APMV]]. (A) Cryo-electron micrograph of four CroV particles. (B) Single CroV particle with concave core depression (white arrow). (C) Single APMV particle. Scale bars in (A–C) represent 2,000 Å. ]] |
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What is confusing is the fact that there are so many genes inside of a girus. Normally, viruses are nothing more than an outer membrane and a little [[DNA]] that is just enough to replicate itself. That's it. No will, no ambition, no emotions, no real life. But giruses have a lot more genes than a normal virus. Some genes scientists don't even know what they do! Others are needed to get [[oxygen]], to [[Photosynthesis|photosynthesize]], to move or to just be alive. Some giruses are even seen to seem to have a certain amount of self-propulsion, like the [[pandoravirus]]. And still they don't seem to be alive. This is one of the mysteries that science just can't solve.[[File:CroV TEM.jpg|thumb|Cryo-EM images of the giant viruses [[CroV]] and [[APMV]]. (A) Cryo-electron micrograph of four CroV particles. (B) Single CroV particle with concave core depression (white arrow). (C) Single APMV particle. Scale bars in (A–C) represent 2,000 Å. ]] |
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=== Hunt For Prey === |
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Giant viruses replicate within large spheroidal [[viroplasm|virus factories]] located within the [[cytoplasm]] of the infected host cell. This is similar to the replication mechanism used by ''[[Poxviridae]]'',{{NoteTag|Which includes the virus that causes [[smallpox]]}} though whether this mechanism is employed by all giant viruses or only mimivirus and the related [[mamavirus]] has yet to be determined.<ref name=Comm-005-1/> These virion replication factories can themselves be infected by the [[virophage]] [[satellite virus]]es, which inhibit or impair the reproduction of the complementary virus. |
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Giant viruses hunt [[Protist|protists]], [[bacteria]] and [[Amoeba|amoebas]]. They use the host cell's defense systems to get inside. They then large spheroidal [[viroplasm]] or virus factories located within the [[cytoplasm]] of the infected host cell in which they replicate. They force the host cell to use all it's resources to make more giruses inside the viroplasm. They are even able to make a defensive membrane around the virus factory. When there are a lot of giruses already, they force the host to explode and release the giruses that it created. This is similar to the replication mechanism used by ''[[Poxviridae]].'' |
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== Virophages == |
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Giant viruses from the deep ocean, terrestrial sources, and human patients contain genes encoding [[Cytochrome P450|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.<ref>{{cite journal | vauthors = Lamb DC, Follmer AH, Goldstone JV, Nelson DR, Warrilow AG, Price CL, True MY, Kelly SL, Poulos TL, Stegeman JJ | display-authors = 6 | title = On the occurrence of cytochrome P450 in viruses | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 116 | issue = 25 | pages = 12343–12352 | date = June 2019 | pmid = 31167942 | pmc = 6589655 | doi = 10.1073/pnas.1901080116 | doi-access = free }}</ref> |
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Even though giruses are very big, there are still viruses that hunt them. [[Virophage]] [[satellite virus]]es,such as Sputnik 1, ride with the giruses as they enter a victim amoeba. Inside the amoeba, the virophages implement their [[DNA]] to the girus's viroplasm, making the girus make only a few copies of itself, which are mostly incomplete. Instead, the viroplasm makes more virophages. In the end, the victim still dies, but the new virophages go out to find more giruses to hijack. |
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=== Defense Against Giruses === |
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The victims of giruses still are not undefended though. Some protists have learned to defend themselves by adding the [[DNA]] of virophages to their DNA. When a girus infects this protist, the protist makes some virophages that use the viroplasm to their own uses. The protist still dies, but instead of making more giruses to kill it's companions, virophages go on the hunt for giruses. |
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== History == |
== History == |
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| Megaviricetes | |
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| Mimivirus | |
Virus classification 
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| (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] They have extremely large genomes compared to other viruses and contain many unique genes not found in life forms. 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]
What is confusing is the fact that there are so many genes inside of a girus. Normally, viruses are nothing more than an outer membrane and a little DNA that is just enough to replicate itself. That's it. No will, no ambition, no emotions, no real life. But giruses have a lot more genes than a normal virus. Some genes scientists don't even know what they do! Others are needed to get oxygen, to photosynthesize, to move or to just be alive. Some giruses are even seen to seem to have a certain amount of self-propulsion, like the pandoravirus. And still they don't seem to be alive. This is one of the mysteries that science just can't solve.
Giant viruses hunt protists, bacteria and amoebas. They use the host cell's defense systems to get inside. They then large spheroidal viroplasm or virus factories located within the cytoplasm of the infected host cell in which they replicate. They force the host cell to use all it's resources to make more giruses inside the viroplasm. They are even able to make a defensive membrane around the virus factory. When there are a lot of giruses already, they force the host to explode and release the giruses that it created. This is similar to the replication mechanism used by Poxviridae.
Even though giruses are very big, there are still viruses that hunt them. Virophage satellite viruses,such as Sputnik 1, ride with the giruses as they enter a victim amoeba. Inside the amoeba, the virophages implement their DNA to the girus's viroplasm, making the girus make only a few copies of itself, which are mostly incomplete. Instead, the viroplasm makes more virophages. In the end, the victim still dies, but the new virophages go out to find more giruses to hijack.
The victims of giruses still are not undefended though. Some protists have learned to defend themselves by adding the DNA of virophages to their DNA. When a girus infects this protist, the protist makes some virophages that use the viroplasm to their own uses. The protist still dies, but instead of making more giruses to kill it's companions, virophages go on the hunt for giruses.
The first giant virus, then named BV-PW1, was isolated and described in 1995,[7] but was not recognized as such until its sequenced genome was released as Cafeteria roenbergensis virus (CroV) in 2010.[8] Subsequently, the Giant Virus Acanthamoeba polyphaga Mimivirus was characterized,[9] (which had been mistaken as a bacterium in 1993),[10] and then sequenced.[11] The term "girus" was coined to refer to the group in 2006.[12]
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.[13] 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.[14][15]
| Giant virus name | Genome Length | Genes | Capsid diameter (nm) | Hair cover | Genbank # |
|---|---|---|---|---|---|
| Bodo saltans virus[16] | 1,385,869 | 1227 proteins (predicted) | ~300 | yes (~40 nm) | MF782455 |
| Megavirus chilensis[17] | 1,259,197 | 1120 proteins (predicted) | 440 | yes (75 nm) | JN258408 |
| Mamavirus[18] | 1,191,693 | 1023 proteins (predicted) | 500 | yes (120 nm) | JF801956 |
| Mimivirus[11][19] | 1,181,549 | 979 proteins 39 non-coding | 500 | yes (120 nm) | NC_014649 |
| M4[20] (Mimivirus "bald" variant) | 981,813 | 756 proteins (predicted) | 390 | No | JN036606 |
| Tupanvirus[21] | 1,500,000 | 1276–1425 proteins | ≥450+550[22] | KY523104 MF405918[23] | |
| Cafeteria roenbergensis virus[24] | 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.[25]
| Giant virus name | Aminoacyl-tRNA synthetase | Octocoral-like 1MutS | 2Stargate[26] | Known virophage[27] | 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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| Nucleic acid self-replication |
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| See also |
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