Giant virus
A giant virus is a very large virus. They are sometimes called a girus. Some of them are larger than typical bacteria.[1][2] All known giant viruses belong to the phylum Nucleocytoviricota.[3]
| Megaviricetes | |
|---|---|
 | |
| Mimivirus | |
Virus classification  | |
| (unranked): | Virus |
| Realm: | Varidnaviria |
| Kingdom: | Bamfordvirae |
| Phylum: | Nucleocytoviricota |
| Class: | Megaviricetes |
The genomes of many giant viruses code for unusual genes which are not found in other viruses. These include genes involved in glycolysis and the TCA cycle,[4] fermentation,[5] and the cytoskeleton.[6][7][8]
The first giant viruses to be described were discovered in 1981.[9]
Note, in the illustration from an electron microscope, the virus is surrounded by a thick (~100 nm) layer of filamentous protein fibres.
Origin
There are two main hypotheses. Either they evolved from small viruses by picking up DNA from host organisms; or they evolved from very complicated organisms by genome reduction.[10]