Zamilon virophage

Zamilon was discovered in 2013, in Acanthamoeba polyphaga amoebae co-infected with the giant virus Mont1, isolated from a Tunisian soil sample. As of 2015, Zamilon is one of three virophages to have been isolated physically, the others being Sputnik and Mavirus; several other virophage DNAs have been discovered using metagenomics but have not been characterised physically. A related strain, named Zamilon 2, was discovered by metagenomic analysis of a North American poplar wood chip bioreactor in 2015. Another virophage, Rio Negro, is also closely related to Sputnik. ==Taxonomy==

Zamilon virophage has been classified by the International Committee on Taxonomy of Viruses into the species Sputnikvirus zamilonense within the genus Sputnikvirus in the family Sputniviroviridae. ==Virology==

A Zamilon virion is spherical with a diameter of 50–60 nm, and is similar in appearance to those of Sputnik and Mavirus. ORF6 is very similar to the Sputnik major capsid protein, which has a double "jelly-roll" fold. ==Life cycle and helper virus==

Like all other virophages, Zamilon replicates in the cytoplasm, within the virus factory of its helper, which acts as its host. This is unlike Sputnik, which can replicate in association with any Mimivirus-like member of Mimiviridae. Zamilon does not appear to inhibit the ability of its helper virus to replicate significantly, nor to lyse its host amoebae cells. Although the helper virus formed a high proportion of abnormal virions in the presence of Zamilon, these were also observed at a comparable level in the virophage's absence. This is again unlike Sputnik, which reduces its helper virus's infectivity, inhibits its lysis of amoeba, and is associated with the generation of an increased proportion of abnormal Mimiviridae virions. Bernard La Scola and colleagues, who isolated both Sputnik and Zamilon, state that, if confirmed, this "would question the concept of virophage", which has been considered to be differentiated from most other satellite viruses in having a deleterious effect on its helper virus. File:Zamilon and abnormal Mont1 (Gaia et al. Fig 3a).jpg| Electron micrograph of a virus factory in an amoeba co-infected with Zamilon virophage (small particles) and Mont1. Arrows show abnormal Mont1 particles (scale bar: 0.1 μm) File:Zamilon virophage with Mont1 (Gaia et al Fig1e).jpg| Electron micrograph of virus factory in an amoeba co-infected with Zamilon and Mont1 (scale bar: 0.1 μm) ==References==