Megavirus
is a
viral genus containing a single identified species named ''Megavirus chilensis'', phylogenetically related to Acanthamoeba polyphaga
Mimivirus
''Mimivirus'' is a genus of giant viruses, in the family '' Mimiviridae''. Amoeba serve as their natural hosts. This genus contains a single identified species named ''Acanthamoeba polyphaga mimivirus'' (APMV). It also refers to a group of phyl ...
(APMV).
In colloquial speech, Megavirus chilensis is more commonly referred to as just “Megavirus”. Until the discovery of
pandoravirus
''Pandoravirus'' is a genus of giant virus, first discovered in 2013. It is the second largest in physical size of any known viral genus. Pandoraviruses have double stranded DNA genomes, with the largest genome size (2.5 million base pairs) of ...
es in 2013, it had the largest
capsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...
diameter of all known viruses, as well as the largest and most complex
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
among all known viruses.
Discovery
Megavirus was isolated from a water sample collected in April 2010 off the coast of
Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, near the marine station in Las Cruces, by Jean-Michel Claverie and Chantal Abergel from the Structural & Genomic Information laboratory (IGS, CNRS and Aix-Marseille University). Megavirus was isolated by co-cultivation with a variety of ''
Acanthamoeba
''Acanthamoeba'' is a genus of amoebae that are commonly recovered from soil, fresh water, and other habitats.
''Acanthamoeba'' has two evolutive forms, the metabolically active trophozoite and a dormant, stress-resistant cyst. Trophozoites are ...
'' laboratory strains (''
A. polyphaga'', ''
A. castellanii'', ''
A. griffini'') following a protocol pioneered by Timothy Rowbotham for isolating intracellular parasitic bacteria.
Megavirus infects amoebas.
Structure
The Megavirus particle exhibits a protein
capsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...
diameter of 440
nanometres (as seen by electron microscopy on thin sections of epoxy resin inclusions), enclosed into a solid mesh of bacterial-like capsular material 75 nm to 100 nm thick. The capsid appears hexagonal, but its icosahedral symmetry is imperfect, due to the presence of the “stargate”, at a single specific vertex of the icosahedron. The stargate is a five-pronged star structure forming the portal through which the internal core of the particle is delivered to the host's cytoplasm. This core is enclosed within two lipid membranes in the particle, also containing a large and diverse complement of viral proteins (e.g. the all transcriptional complex). Surprisingly, the Megavirus is larger than some bacteria.
Genome
The Megavirus chilensis genome is a linear, double-stranded molecule of
DNA with 1,259,197
base pairs in length. It exhibits 7
aminoacyl tRNA synthetases (Table 2), the archetypes of enzymes previously thought only to be encoded by cellular organisms. While 4 of these enzymes were known to be present in Mimivirus and Mamavirus (for tyrosine, arginine, cysteine, and methionine), Megavirus exhibits three more (for tryptophan, asparagine, and isoleucine).
See also
*
Mimivirus
''Mimivirus'' is a genus of giant viruses, in the family '' Mimiviridae''. Amoeba serve as their natural hosts. This genus contains a single identified species named ''Acanthamoeba polyphaga mimivirus'' (APMV). It also refers to a group of phyl ...
– the giant virus that revolutionized virology
*
Cafeteria roenbergensis virus – the largest marine virus
*
Parvovirus
Parvoviruses are a family of animal viruses that constitute the family ''Parvoviridae''. They have linear, single-stranded DNA (ssDNA) genomes that typically contain two genes encoding for a replication initiator protein, called NS1, and the p ...
– smallest known single stranded DNA
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
es
*
Pithovirus - largest virus by capsid length (approximately 1.5
micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
)
*
Pandoraviridae
''Pandoraviridae'' is a family of DNA virus#Group I: dsDNA viruses, double-stranded DNA viruses that infect amoebae. There is only one genus in this family: ''Pandoravirus''. Several species in this genus have been described, including ''Pandora ...
- second largest virus by capsid length (approximately 1 micrometre)
*
Virophage
References
External links
GiantVirus.org– an information resource on the genome of giant viruses.
International Committee on Taxonomy of Viruses (ICTV) picture gallery- images of mimivirus
*
{{Taxonbar, from=Q285598
Mimiviridae