Mimivirus
Virus classification
Group: Group I (dsDNA) Species: Acanthamoeba polyphaga mimivirus

Mimivirus is a viral genus containing a single identified species named Acanthamoeba polyphaga mimivirus (APMV). In colloquial speech, APMV is more commonly referred to as just “mimivirus”. It has the largest capsid diameter of all known viruses, as well as a large and complex genome compared to other viruses. Though knowledge on the virus is relatively limited, the discovery of the virus excited many people due to the implications of its complex nature, with people hailing it as everything from a new domain of life to a missing link between viruses and bacteria. This article explains how to read a taxobox. ... Image File history File links Download high-resolution version (822x624, 95 KB) An infographic/illustration of mimivirus, based upon various web-based sources, including giantvirus. ... Virus classification involves naming and placing viruses into a taxonomic system. ... A DNA virus is a virus that has DNA as its genetic material and does not use an RNA intermediate during replication. ... Groups I: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (-)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A virus (Latin, poison) is a microscopic particle that can infect the cells of a biological organism. ... The outer shell of a virus is called the capsid. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...

Discovery

APMV was discovered serendipitously in 1992 within the amoeba Acanthamoeba polyphaga, for which it is named, during research into Legionellosis. The virus was observed in a gram stain and mistakenly thought to be a gram-positive bacterium. As a consequence it was named "Bradfordcoccus", after the district the amoeba was sourced from in Bradford, England. In 2003, researchers at the Université de la Méditerranée in Marseille, France published a paper in Science identifying the micro-organism as a virus^[1]. Amoeba, amÅ“ba, or ameba is a genus of protozoa that moves by means of temporary projections called pseudopods, and is well-known as a representative unicellular organism. ... Legionellosis is an infection caused by the genus of Gram negative bacteria Legionella, notably Legionella pneumophila. ... Gram staining is a method for staining samples of bacteria that differentiates between the two main types of bacterial cell wall. ... Gram-positive bacteria are those that are stained dark blue or violet by gram staining, in contrast to gram-negative bacteria, which are not affected by the stain. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... The larger City of Bradford Metropolitan District includes other settlements in the surrounding area. ... Motto: (French for God and my right) Anthem: God Save the King/Queen Capital London Largest city London Official language(s) English (de facto) Unification    - by Athelstan AD 927  Area    - Total 130,395 km² (1st in UK)   50,346 sq mi  Population    - 2006 est. ... The Université de la Méditerranée Aix-Marseille II is one of the University of Aix-Marseille based across the the communes of Aix-en-Provence and Marseille in southern France. ... City flag Coat of arms Motto: By her great deeds, Marseille shines in the world Location Coordinates Time Zone CET (GMT +1) Administration Country France Region Provence-Alpes-Côte dAzur Department Bouches-du-Rhône (13) Subdivisions 16 arrondissements (in 8 secteurs) Intercommunality Urban Community of Marseille Provence... Science is the journal of the American Association for the Advancement of Science (AAAS). ...

Mimivirus may be a causative agent of some forms of pneumonia, however, this is a tentative proposal based solely on indirect evidence in the form of antibodies to the virus discovered in pneumonia patients. Although it was once a suspect in the pneumonia outbreak in Bradford, today scientists believe that the virus can only infect amoebae.. The larger City of Bradford Metropolitan District includes other settlements in the surrounding area. ...

Classification

It has not been placed into a viral family by the International Committee on Taxonomy of Viruses but more members of the proposed family Mimiviridae are thought to exist based on metagenomic data.^[2] It has however, been placed into Group I of the Baltimore classification system. This page is a candidate to be copied to Wikisource. ... Metagenomics (also Environmental Genomics, Ecogenomics or Community Genomics) is the study of genomes recovered from environmental samples as opposed to from clonal cultures. ... Virus classification involves naming and placing viruses into a taxonomic system. ... Virus classification involves naming and placing viruses into a taxonomic system. ...

Whilst not strictly a method of classification, Mimivirus joins a group of large viruses known as nucleocytoplasmic large DNA viruses (NCLDV), which includes four other families: Poxviridae, Iridoviridae, Phycodnaviridae and Asfarviridae. They are all large viruses which share both molecular characteristics and large genomes. The mimivirus genome also possesses 21 genes encoding homologs to proteins which are seen to be highly conserved in the majority of NCLDVs, and further work suggests that mimivirus is an early divergent of the general NCLDV group^[1]. Genera Subfamily Chordopoxvirinae    Orthopoxvirus    Parapoxvirus    Avipoxvirus    Capripoxvirus    Leporipoxvirus    Suipoxvirus    Molluscipoxvirus    Yatapoxvirus Subfamily Entomopoxvirinae    Entomopoxvirus A    Entomopoxvirus B    Entomopoxvirus C Poxviruses (members of the family Poxviridae) can infect as a family both vertebrate and invertebrate animals. ... Phycodnaviruses (members of the family Phyvodnaviridae) are large (160 to 560 thousand base pairs), dobule stranded DNA viruses that infect marine or freshwater eukaryotic algae. ...

Structure

Mimivirus is the largest known virus, with a capsid diameter of 400 nm. Protein filaments measuring 100 nm project from the surface of the capsid, bringing the total length of the virus up to 600 nm. Variation in scientific literature renders these figures as highly approximate, with the “size” of the virion being casually listed as anywhere between 400 nm and 800 nm, depending on whether total length or capsid diameter is actually quoted. The capsid appears hexagonal under an electron microscope, therefore the capsid symmetry is icosahedral. It does not appear to possess an outer viral envelope, suggesting that the virus does not exit the host cell by exocytosis^[3]. The outer shell of a virus is called the capsid. ... A metre (American spelling: meter; symbol: m) is a unit of length and the current base unit of length in the International System of Units (SI). ... A common alternate meaning of virus is computer virus. ... A transmission electron microscope. ... Groups I: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (-)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A virus (Latin, poison) is a microscopic particle that can infect the cells of a biological organism. ... This page is currently under construction. ...

Mimivirus shares several morphological characteristics in common with all members of the NCLDV group of viruses. As an internal lipid layer surrounding the central core is present in all other NCLDV viruses, it has been suggested by M. Suzan-Monti et al. that this may also be present in mimivirus. The condensed central core of the virion appears as a dark region under the electron microscope. The large genome of the virus resides within this area.

Several mRNA transcripts can be recovered from purified virions. Like other NCLDVs, transcripts for DNA polymerase, a capsid protein and a TFII-like transcription factor were found. However, three distinct aminoacyl tRNA synthetase enzyme transcripts and four unknown mRNA molecules specific to mimivirus were also found. These pre-packaged transcripts can be translated without viral gene expression and are likely to be necessary to Mimivirus for replication. Other DNA viruses, such as the Human cytomegalovirus and Herpes simplex virus type-1, also feature pre-packaged mRNA transcripts (M. Suzan-Monti, 2006). The interaction of mRNA in a eukaryote cell. ... 3D structure of the DNA-binding helix-hairpin-helix motifs in human DNA polymerase beta A DNA polymerase is an enzyme that assists in DNA replication. ... The outer shell of a virus is called the capsid. ... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... An aminoacyl tRNA synthetase (abbreviated aaRs) is an enzyme that catalyzes the binding of a specific amino acid to a tRNA to form an aminoacyl-tRNA. The synthetase hydrolyzes ATP to bind the appropriate amino acid to the 3 hydroxyl of the tRNA molecule. ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... Species see text Cytomegalovirus (CMV), is a genus of Herpes viruses; in humans the species is known as Human herpesvirus 5 (HHV-5). ... It has been suggested that this article or section be merged with Herpes simplex virus. ...

Genome

The mimivirus genome is a linear, double-stranded molecule of DNA roughly 1.2 million base pairs in length. This makes it the largest viral genome in scientific knowledge, outstripping the next-largest virus genome of the myovirus Bacillus phage G by a little over double. In addition, it is larger than at least 30 cellular organisms^[4]. The structure of part of a DNA double helix. ... Base pairs, of a DNA molecule. ... Genera T4-like viruses P1-like viruses P2-like viruses Mu-like viruses SPO1-like viruses φH-like viruses The Myoviridae are a family of bacteriophages, including the following genera: Genus T4-like viruses; type species: Enterobacteria phage T4, others include Enterobacteria phage T2 Genus P1-like viruses; type...

In addition to the large size of the genome, mimivirus possesses an estimated 911 protein-coding genes, far exceeding the minimum 4 genes required for viruses to exist (c.f. MS2 and Qβ viruses^[5]). Analysis of its genome revealed the presence of genes not seen in any other viruses, including aminoacyl tRNA synthetases, and other genes thought only to be encoded by cellular organisms. Like other large DNA viruses, mimivirus contains several genes for sugar, lipid and amino acid metabolism, as well as some metabolic genes not found in any other virus (M. Suzan-Monti, 2006). Roughly 90% of the genome was of coding capacity, with the other 10% being “junk DNA”. For other meanings of this term, see gene (disambiguation). ... An aminoacyl tRNA synthetase (abbreviated aaRs) is an enzyme that catalyzes the binding of a specific amino acid to a tRNA to form an aminoacyl-tRNA. The synthetase hydrolyzes ATP to bind the appropriate amino acid to the 3 hydroxyl of the tRNA molecule. ... In molecular biology, junk DNA is a collective label for the portions of the DNA sequence of a chromosome or a genome for which no function has yet been identified. ...

Replication

The stages of mimivirus replication are not well known, but as a minimum it is known that mimivirus attaches to a chemical receptor on the surface of an amoeba cell and is taken into the cell. Once inside, an eclipse phase begins, in which the virus disappears and all appears normal within the cell. After about four hours small accumulations can be seen in areas of the cell. Eight hours after infection many mimivirus virions are clearly visible within the cell. The cell cytoplasm continues to fill with newly synthesised virions and about 24 hours after initial infection the cell likely bursts open to release the new mimivirus virions (M. Suzan-Monti, 2006). In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ... Cytoplasm is a water-like cell wall that fills cells. ...

Little is known about the details of this replication cycle, most obviously attachment to the cell surface and entry, viral core release, DNA replication, transcription, translation, assembly and release of progeny virions. However, scientists have established the general overview given above using electron micrographs of infected cells. These micrographs show mimivirus capsid assembly in the nucleus, acquisition of an inner lipid membrane via budding from the nucleus, and particles similar to those found in many other viruses, including all NCLDV members. These particles are known in other viruses as viral factories and allow efficient viral assembly by modifying large areas of the host cell. An electron micrograph is a micrograph made with an electron microscope. ...

Implications for life

Mimivirus possesses many characteristics which place it at the boundary of living and non-living. It is as large as several bacterial species, namely Rickettsia conorii and Tropheryma whipplei, possesses a genome of comparable size to several bacteria, including those above, and codes for products previously not thought to be encoded by viruses. In addition, mimivirus possesses genes coding for nucleotide and amino acid synthesis, which even some small obligate intracellular bacteria lack. This means that unlike these bacteria, mimivirus is not dependent on the host cell genome for coding the metabolic pathways for these products. They do however, lack genes for ribosomal proteins, making mimivirus dependent for protein translation and energy metabolism. These factors combined have thrown scientists into debate over whether mimivirus is a distinct form of life, comparable on a domain scale to Eukarya, Archaea and Bacteria. However, it should be noted that mimivirus does not undergo cellular division, currently a basic requirement for life, instead replicating via self-assembly of individual components. Species Rickettsia felis Rickettsia prowazekii Rickettsia rickettsii Rickettsia typhi Rickettsia conorii etc. ... Whipples disease is a rare disease caused by the bacteria Thropheryma whipplei. ... In biology, a domain or empire is the top-level grouping of organisms in scientific classification. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota Archaea (; from Greek αρχαία, ancient ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), is a major division of living organisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...

Because its lineage is very old and could have emerged prior to cellular organisms, mimivirus has added to the debate over the origins of life. Some genes unique to mimivirus, including those coding for the capsid, have been conserved in a variety of viruses which infect organisms from all domains - Eukarya, Archaea and Bacteria. This has been used to suggest that mimivirus is related to a type of DNA virus that emerged before cellular organisms and played a key role in the development of all life on Earth^[6]. An alternative hypothesis is that there were three distinct types of DNA viruses that were involved in generating the three known domains of life ^[7]. Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota Archaea (; from Greek αρχαία, ancient ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), is a major division of living organisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... In biology, a domain (also superregnum, superkingdom, or empire) is the top-level grouping of organisms in scientific classification, higher than a kingdom. ...

Other resources

See also

• Mycoplasma genitalium - one of the smallest bacteria
• Pelagibacter ubique - possesses one of the smallest bacterial genomes
• Nanoarchaeum equitans - smallest known independent cell, smallest known genome
• Nanobacterium
• Nanobe
• Parvovirus - smallest known family of viruses

Binomial name Mycoplasma genitalium Mycoplasma genitalium is a parasitic bacterium which lives in the primate genital and respiratory tracts. ... Binomial name Candidatus Pelagibacter ubique Rappé et al. ... Binomial name Nanoarchaeum equitans Nanoarchaeum equitans is a species of tiny microbe, discovered in 2002 in a hydrothermal vent off the coast of Iceland by Karl Stetter. ... Structures found on meteorite fragment ALH84001 Nanobacteria are said to be cell walled microorganisms with a diameter well below the generally accepted lower limit (about 200 nanometres) for bacteria. ... A nanobe Nanobes are tiny filamental structures first found in some rocks and sediments and also some poo like the poo that comes out your ass hole you know the stuff that smells real bad and sticks to your fingers! Some hypothesize that they are the smallest form of life... Species Canine minute virus Canine parvovirus Chicken parvovirus Feline panleukopenia virus Feline parvovirus HB virus H-1 virus Kilham rat virus Lapine parvovirus LUIII virus Mice minute virus Mink enteritis virus Mouse parvovirus 1 Porcine parvovirus Raccoon parvovirus RT parvovirus Tumor virus X Parvovirus, commonly called parvo, is a genus... Groups I: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (-)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A virus (Latin, poison) is a microscopic particle that can infect the cells of a biological organism. ...

External links

• The Big Picture Book of Viruses - images of mimivirus

Footnotes

Science is the journal of the American Association for the Advancement of Science (AAAS). ... The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences. ...

References