Giant virus
A giant 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]
Description
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)[4] 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).[3][5] 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.[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
History
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.[13][14]
Other giant viruses that infected marine flagellates were described later. The first mimivirus (BV-PW1) was described in 1995,[15] but was not recognized as such until its sequenced genome was released as Cafeteria roenbergensis virus (CroV) in 2010.[16] Subsequently, the Giant Virus Acanthamoeba polyphaga Mimivirus was characterized[17] (which had been mistaken as a bacterium in 1993),[18] and then sequenced.[19] The term "girus" was coined to refer to the group in 2006.[20]
Genetics and evolution
The genomes of giant viruses are the largest known for viruses, and contain genes that encode for important elements of
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.[21] The possible complicated ancestral organism is also a topic of debate: by one proposal, it might represent a fourth domain of life,[5] but this has been largely discounted.[22][23][24]
Comparison of largest known giant viruses
Giant virus name | Genome Length | Genes | Capsid diameter (nm) | Hair cover | Genbank # |
---|---|---|---|---|---|
Bodo saltans virus[25] | 1,385,869 | 1227 proteins (predicted) | ~300 | yes (~40 nm) | MF782455 |
Megavirus chilensis[26] |
1,259,197 | 1120 proteins (predicted) | 440 | yes (75 nm) | JN258408 |
Mamavirus[27] | 1,191,693 | 1023 proteins (predicted) | 500 | yes (120 nm) | JF801956 |
Mimivirus[19][28] | 1,181,549 | 979 proteins 39 non-coding | 500 | yes (120 nm) | NC_014649 |
M4[29] (Mimivirus "bald" variant) | 981,813 | 756 proteins (predicted) | 390 | No | JN036606 |
Tupanvirus[30] | 1,500,000 | 1276–1425 proteins | ≥450+550[31] | KY523104 MF405918[32] | |
Cafeteria roenbergensis virus[33] | 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.[34] As of June 11, 2018, there were 183 listed.[35]
Giant virus name | Aminoacyl-tRNA synthetase | Octocoral-like 1MutS | 2Stargate[36] | Known virophage[37] | 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.
See also
- Cafeteria roenbergensis virus
- Klosneuvirus
- Mimivirus
- Nucleocytoviricota
- Pandoravirus
- Pithovirus
- Mamavirus
References
- ^ Reynolds KA (2010). "Mysterious Microbe in Water Challenges the Very Definition of a Virus" (PDF). Water Conditioning & Purification. Archived from the original (PDF) on 2014-03-19.
- PMID 19860921.
- ^ doi:10.1511/2011.91.304. Archived from the originalon 2011-06-21.
- PMID 28710447.
- ^ PMID 22482024.
- PMID 31167942.
- PMID 32249765.
- PMID 29649682.
- S2CID 219947620.
- PMID 34254826.
- PMID 34163457.
- PMID 34705818.
- PMID 18635088.
- PMID 20831832.
- .
- PMID 20974979.
- S2CID 39606235.
- ^ "Giant Viruses". American Scientist. 2017-02-06. Retrieved 2021-09-02.
- ^ S2CID 84298461.
- S2CID 8791457.
- ^ Bichell RE. "In Giant Virus Genes, Hints About Their Mysterious Origin". All Things Considered.
- S2CID 206655792.
- PMID 30837339.
- PMID 25042053.
- PMID 29582753.
- PMID 21987820.
- PMID 21705471.
- PMID 21375749.
- PMID 21646533.
- PMID 29487281.
- ^ head and tail, respectively
- ^ soda lake and deep ocean species of Tupanvirues, respectively
- PMID 20974979.
- ^ "Giant Virus Toplist". PIT Bioinformatics Group, Department of Computer Science. Eötvös University. 2015-03-26.
- ^ "Giant Virus Toplist". PIT Bioinformatics Group. 26 March 2015. Retrieved 10 May 2023.
- PMID 18479185.
- S2CID 206530677.