''Megavirus''
is a
viral genus, phylogenetically related to ''
Acanthamoeba polyphaga mimivirus'' (APMV).
In colloquial speech, ''Megavirus chilense'' is more commonly referred to as just "Megavirus". Until the discovery of
pandoravirus
''Pandoravirus'' is a proposed genus of giant virus, first discovered in 2013. It is the third largest in physical size of any known viral genus, behind Pithovirus and Megaklothovirus. Pandoraviruses have double stranded DNA genomes, with t ...
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 m ...
diameter of all known viruses, as well as the largest and most complex
genome
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 genes, other functional regions of the genome such as ...
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 western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...
, 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 amoeboid, amoebae that are commonly recovered from soil, fresh water, and other habitat (ecology), habitats.
The genus ''Acanthamoeba'' has two stages in its life cycle, the metabolically active trophozoite stage a ...
'' laboratory strains (''
Acanthamoeba polyphaga'', ''
Acanthamoeba castellanii'', ''
Acanthamoeba 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 m ...
diameter of 440
nanometre
330px, Different lengths as in respect to the Molecule">molecular scale.
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling), is a unit of length ...
s (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 chilense'' genome is a linear, double-stranded molecule of
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
with 1,259,197
base pairs
A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...
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''. It is believed that Amoeba serve as their natural hosts. It also refers to a group of phylogenetically related large viruses.
In colloquial speech, APMV is more commonly ...
'' – 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 Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
es
* ''
Pithovirus
''Alphapithovirus'', is a genus of giant virus known from two species, '' Alphapithovirus sibericum'', which infects amoebas, and '' Alphapithovirus massiliense''. It is DNA-based and is a member of the nucleocytoplasmic large DNA viruses clade ...
'' – largest virus by capsid length (approximately 1.5
micrometre
The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...
)
* ''
Pandoraviridae
''Pandoraviridae'' is a proposed family of 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 '' Pandoravirus dulcis'', '' Pand ...
'' – second largest virus by capsid length (approximately 1 micrometre)
*
Virophage
References
External links
* – an information resource on the genome of giant viruses.
*
{{Taxonbar, from=Q285598
Mimiviridae
Virus genera