Giant virus

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 in diameter){{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 }} that may be surrounded by a thick (approximately 100 nm) layer of filamentous protein fibers. The viruses have large, double-stranded DNA genomes (300 to >1000 kilobasepairs) that encode a large contingent of genes (of the order of 1000 genes). The best characterized giant viruses are the phylogenetically related mimivirus and megavirus, which belong to the family Mimiviridae (aka Megaviridae), and are distinguished by their large capsid diameters.{{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 }} 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.{{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|bibcode=2019PNAS..11612343L |doi-access=free}}

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,{{cite journal | vauthors = Moniruzzaman M, Martinez-Gutierrez CA, Weinheimer AR, Aylward FO | title = Dynamic genome evolution and complex virocell metabolism of globally-distributed giant viruses | journal = Nature Communications | volume = 11 | issue = 1710 | date = 2020 | page = 1710 | doi = 10.1038/s41467-020-15507-2 | pmid = 32249765 | pmc = 7136201 | bibcode = 2020NatCo..11.1710M }} fermentation,{{cite journal | vauthors = Schvarcz CR, Steward GF | title = A giant virus infecting green algae encodes key fermentation genes | journal = Virology | date = 2018 | volume = 518 | pages = 423–433 | doi = 10.1016/j.virol.2018.03.010 | pmid = 29649682 | doi-access = free }} and the cytoskeleton.{{cite journal | vauthors = Da Cunha V, Gaia M, Ogata H, Jaillon O, Delmont TO, Patrick Forterre P | title = Giant viruses encode novel types of actins possibly related to the origin of eukaryotic actin: the viractins | journal = bioRxiv | year = 2020 | doi = 10.1101/2020.06.16.150565 | s2cid = 219947620 }}{{cite journal | vauthors = Ha AD, Moniruzzaman M, Aylward FO | title = High Transcriptional Activity and Diverse Functional Repertoires of Hundreds of Giant Viruses in a Coastal Marine System | journal = mSystems | volume = 6 | issue = 4 | date = 2021 | pages = e0029321 | doi = 10.1128/mSystems.00293-21 | pmid = 34254826| pmc = 8407384 }}{{cite journal | vauthors = Kijima S, Delmont TO, Miyazaki U, Gaia M, Endo H, Ogata H |title=Discovery of Viral Myosin Genes With Complex Evolutionary History Within Plankton |journal=Frontiers in Microbiology |date=7 June 2021 |volume=12 |pages=683294 |doi=10.3389/fmicb.2021.683294|pmid=34163457 |pmc=8215601 |doi-access=free }}

File:CroV TEM.jpg 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. ]]

File:Journal.pbio.3001430.g002.png

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.{{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}}{{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 |doi-access=free }}

Other giant viruses that infected marine flagellates were described later. The first mimivirus (BV-PW1) was described in 1995,{{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 |journal=Aquatic Microbial Ecology |volume=9 |issue=3 |pages=133–144 |url=https://www.int-res.com/articles/ame/9/a009p203.pdf |doi=10.3354/ame009203 |doi-access=free}} but was not recognized as such until its sequenced genome was released as Cafeteria roenbergensis virus (CroV) in 2010.{{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 }} Subsequently, the Giant Virus Acanthamoeba polyphaga Mimivirus was characterized{{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}} (which had been mistaken as a bacterium in 1993),{{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}} and then sequenced.{{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 }} The term "girus" was coined to refer to the group in 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 }}

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. 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 in the megavirus genome (including those in Mimiviridae) provide evidence that these large DNA viruses may have evolved from a shared cellular genome ancestor by means of genome reduction.

The discovery and subsequent characterization of giant viruses has triggered debate on their evolutionary origins. The two main hypotheses are that they evolved from small viruses by picking up DNA from host organisms; or that they evolved from very complicated organisms via genome reduction, losing various functions including self-reproduction.{{cite news | first = Rae Ellen | last = Bichell | name-list-style = vanc | title = In Giant Virus Genes, Hints About Their Mysterious Origin | url = https://www.npr.org/sections/health-shots/2017/04/06/522478901/in-giant-virus-genes-hints-about-their-mysterious-origin | work = All Things Considered }} The possible complicated ancestral organism is also a topic of debate: by one proposal, it might represent a fourth domain of life, but this has been largely discounted.{{cite journal | vauthors = Schulz F, Yutin N, Ivanova NN, Ortega DR, Lee TK, Vierheilig J, Daims H, Horn M, Wagner M, Jensen GJ, Kyrpides NC, Koonin EV, Woyke T | title = Giant viruses with an expanded complement of translation system components | journal = Science | volume = 356 | issue = 6333 | pages = 82–85 | date = April 2017 | pmid = 28386012 | doi = 10.1126/science.aal4657 | bibcode = 2017Sci...356...82S | s2cid = 206655792 | url = https://escholarship.org/content/qt0kf9t6gn/qt0kf9t6gn.pdf?t=oruwia | doi-access = free }}{{cite journal | vauthors = Bäckström D, Yutin N, Jørgensen SL, Dharamshi J, Homa F, Zaremba-Niedwiedzka K, Spang A, Wolf YI, Koonin EV, Ettema TJ | title = Virus Genomes from Deep Sea Sediments Expand the Ocean Megavirome and Support Independent Origins of Viral Gigantism | journal = mBio | volume = 10 | issue = 2 |pages=e02497-02418 | date = March 2019 | doi = 10.1128/mBio.02497-18 | pmid = 30837339 | pmc = 6401483 }}{{cite journal | vauthors = Yutin N, Wolf Y, Koonin EV | title = Origin of giant viruses from smaller DNA viruses not from a fourth domain of cellular life | journal = Virology | volume = 466–467 | issue = 2014 |pages=38–52 | date = 2014 | doi = 10.1016/j.virol.2014.06.032 | pmid = 25042053 |pmc=4325995 }} A molecular dating study shows that the divergence time of the last common ancestor of the giant viruses was within the last billion years, which is much younger than the origins of the known domains of life.{{cite journal | vauthors = Tee HS, Ku C | title = Host-calibrated time tree caps the age of giant viruses | journal = Molecular Biology and Evolution | volume = 42 | issue = 2 | pages = msaf033 | date = 2025 | pmid = 39976376 | doi = 10.1093/molbev/msaf033 | bibcode = | s2cid = | url = https://academic.oup.com/mbe/article/42/2/msaf033/8026316 | doi-access = free | pmc = 11840718 }}

class="wikitable" |+Largest giant viruses with complete sequenced genomes {{as of|lc=1|2018|06}} !Giant virus name!!Genome Length!!Genes!!Capsid diameter (nm)!!Hair cover!!Genbank #
Pandoravirus salinus{{Cite journal |last1=Pereira Andrade |first1=Ana Cláudia dos Santos |last2=Victor de Miranda Boratto |first2=Paulo |last3=Rodrigues |first3=Rodrigo Araújo Lima |last4=Bastos |first4=Talita Machado |last5=Azevedo |first5=Bruna Luiza |last6=Dornas |first6=Fábio Pio |last7=Oliveira |first7=Danilo Bretas |last8=Drumond |first8=Betânia Paiva |last9=Kroon |first9=Erna Geessien |last10=Abrahão |first10=Jônatas Santos |date=2019-02-19 |title=New Isolates of Pandoraviruses: Contribution to the Study of Replication Cycle Steps |journal=Journal of Virology |volume=93 |issue=5 |pages=10.1128/jvi.01942–18 |doi=10.1128/jvi.01942-18 |pmc=6384056 |pmid=30541841}} |2,473,870 |2500 proteins (predicted) |~500 | |KC977571
Tupanvirus{{cite journal |vauthors=Abrahão J, Silva L, Silva LS, Khalil JY, Rodrigues R, Arantes T, Assis F, Boratto P, Andrade M, Kroon EG, Ribeiro B, Bergier I, Seligmann H, Ghigo E, Colson P, Levasseur A, Kroemer G, Raoult D, La Scola B |date=February 2018 |title=Tailed giant Tupanvirus possesses the most complete translational apparatus of the known virosphere |journal=Nature Communications |volume=9 |issue=1 |pages=749 |bibcode=2018NatCo...9..749A |doi=10.1038/s41467-018-03168-1 |pmc=5829246 |pmid=29487281}} |1,500,000 |1276–1425 proteins |≥450+550head and tail, respectively | |KY523104 MF405918soda lake and deep ocean species of Tupanvirues, respectively
Bodo saltans virus{{cite journal | vauthors = Deeg CM, Chow CT, Suttle CA | title = The kinetoplastid-infecting Bodo saltans virus (BsV), a window into the most abundant giant viruses in the sea | journal = eLife | volume = 7 | pages = e33014 | date = March 2018 | pmid = 29582753 | pmc = 5871332 | doi = 10.7554/eLife.33014 | doi-access = free }}	1,385,869	1227 proteins (predicted)	~300	yes (~40 nm)	MF782455
Megavirus chilense{{cite journal | vauthors = Arslan D, Legendre M, Seltzer V, Abergel C, Claverie JM | title = Distant Mimivirus relative with a larger genome highlights the fundamental features of Megaviridae | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 108 | issue = 42 | pages = 17486–91 | date = October 2011 | pmid = 21987820 | pmc = 3198346 | doi = 10.1073/pnas.1110889108 | bibcode = 2011PNAS..10817486A | doi-access = free }}	1,259,197	1120 proteins (predicted)	440	yes (75 nm)	JN258408
Mamavirus{{cite journal | vauthors = Colson P, Yutin N, Shabalina SA, Robert C, Fournous G, La Scola B, Raoult D, Koonin EV | title = Viruses with more than 1,000 genes: Mamavirus, a new Acanthamoeba polyphaga mimivirus strain, and reannotation of Mimivirus genes | journal = Genome Biology and Evolution | volume = 3 | pages = 737–42 | year = 2011 | pmid = 21705471 | pmc = 3163472 | doi = 10.1093/gbe/evr048 }}	1,191,693	1023 proteins (predicted)	500	yes (120 nm)	JF801956
Mimivirus{{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 }}{{cite journal | vauthors = Legendre M, Santini S, Rico A, Abergel C, Claverie JM | title = Breaking the 1000-gene barrier for Mimivirus using ultra-deep genome and transcriptome sequencing | journal = Virology Journal | volume = 8 | issue = 1 | pages = 99 | date = March 2011 | pmid = 21375749 | pmc = 3058096 | doi = 10.1186/1743-422X-8-99 | doi-access = free }}	1,181,549	979 proteins 39 non-coding	500	yes (120 nm)	NC_014649
M4{{cite journal |pages=10296–301 |doi=10.1073/pnas.1101118108 |pmc=3121840 |title=Mimivirus shows dramatic genome reduction after intraamoebal culture |year=2011 |last1=Boyer |first1=M. |last2=Azza |first2=S. |last3=Barrassi |first3=L. |last4=Klose |first4=T. |last5=Campocasso |first5=A. |last6=Pagnier |first6=I. |last7=Fournous |first7=G. |last8=Borg |first8=A. |last9=Robert |first9=C. |last10=Zhang |first10=X. |last11=Desnues |first11=C. |last12=Henrissat |first12=B. |last13=Rossmann |first13=M. G. |last14=La Scola |first14=B. |last15=Raoult |first15=D. |journal=Proceedings of the National Academy of Sciences |volume=108 |issue=25 |pmid=21646533|bibcode=2011PNAS..10810296B |display-authors=8 |doi-access=free }} (Mimivirus "bald" variant)	981,813	756 proteins (predicted)	390	No	JN036606
Cafeteria roenbergensis virus{{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 }}	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.{{cite web | title = Giant Virus Toplist | url = http://pitgroup.org/giant-virus-toplist/ | work = PIT Bioinformatics Group, Department of Computer Science | publisher = Eötvös University | date = 2015-03-26 }} As of June 11, 2018, there were 183 listed.{{cite web |title=Giant Virus Toplist |date=26 March 2015 |url=https://pitgroup.org/giant-virus-toplist/ |publisher=PIT Bioinformatics Group |access-date=10 May 2023}}

class="wikitable" |+Specific common features among giant viruses !Giant virus name!!Aminoacyl-tRNA synthetase!!Octocoral-like 1MutS!!2Stargate{{cite journal | vauthors = Zauberman N, Mutsafi Y, Halevy DB, Shimoni E, Klein E, Xiao C, Sun S, Minsky A | title = Distinct DNA exit and packaging portals in the virus Acanthamoeba polyphaga mimivirus | journal = PLOS Biology | volume = 6 | issue = 5 | pages = e114 | date = May 2008 | pmid = 18479185 | pmc = 2430901 | doi = 10.1371/journal.pbio.0060114 | editor1-last = Sugden | editor1-first = Bill | doi-access = free }}!!Known virophage{{cite journal | vauthors = Fischer MG, Suttle CA | title = A virophage at the origin of large DNA transposons | journal = Science | volume = 332 | issue = 6026 | pages = 231–4 | date = April 2011 | pmid = 21385722 | doi = 10.1126/science.1199412 | bibcode = 2011Sci...332..231F | s2cid = 206530677 }}!!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.

{{Portal|Viruses}}

• Cafeteria roenbergensis virus
• Klosneuvirus
• Mimivirus
• Nucleocytoviricota
• Pandoravirus
• Pithovirus
• Mamavirus

{{Reflist}}

{{Baltimore classification}}

{{Self-replicating organic structures}}

Category:Nucleocytoplasmic large DNA viruses