Sputnik virophage
Encyclopedia
Sputnik virophage is a subviral agent that reproduces in amoeba
cells that are already infected by a certain helper virus; Sputnik uses the helper virus's machinery for reproduction and inhibits replication of the helper virus.
Viruses like Sputnik that depend on co-infection of the host
cell by helper viruses are known as satellite viruses
. At its discovery in a Paris water-cooling tower in 2008 Sputnik was the first known satellite virus that inhibited replication of its helper virus and thus acted as a parasite of that virus. In analogy to the term bacteriophage
it was called a virophage.
in shape and 50 nanometre
s in size. It has been found to multiply inside of Acanthamoeba
species, but only if that amoeba is infected with the large mamavirus
. Sputnik harnesses the mamavirus proteins to rapidly produce new copies of itself.
Mamavirus is formally known as Acanthamoeba polyphaga
mimivirus (APMV) and is a close relative of the previously known mimivirus
. The mimivirus is a giant in the viral world; it has more genes than many bacteria and performs functions that normally occur only in cellular organisms. The mamavirus is even larger than the mimivirus, but the two are very similar in that they form large viral factories and complex viral particles. Virophage growth is deleterious to APMV and results in the production of abortive forms and abnormal capsid assembly of APMV. In one of the experiments done by inoculating Acanthamoeba polyphaga
with water containing an original strain of APMV, it was discovered that several capsid layers accumulate unsymmetrically on one side of the viral particle causing the virus to become ineffective. Sputnik decreased the yield of infective viral particle by 70% and also reduced the amoeba lysis by threefold at 24h.
Sputnik has a circular double stranded DNA
genome
consisting of 18,343 base pairs. It contains genes able to infect all three domains of life: Eukarya, Archaea
and Bacteria
.
Of the twenty-one predicted protein-coding genes, three are apparently derived from APMV itself, one is a homologue of an archaeal virus, and four others are homologues of proteins in bacteriophages and eukaryotic viruses. Thirteen are ORFans
, that is they do not have any detectable homologues in current sequence databases. The Sputnik genome has a high A + T content (73%) similar to that of APMV.
Several other homologues such as those of a primase–helicase, a packaging ATPase, an insertion sequence transposase DNA-binding subunit, and a Zn-ribbon protein, were detected in the Global Ocean Survey
environmental data set, suggesting that virophages could be a currently unknown family of viruses.
Sputnik was found to contain genes that were shared by APMV. These genes could have been acquired by Sputnik after the association of APMV with the host and then interaction between the virophage and the viral host. Recombination within the viral factory might have resulted in the exchange of genes. Sputnik is one of the most convincing pieces of evidence for gene mixing and matching between viruses.
The presence of these genes homologous to the mimivirus in Sputnik suggests that gene transfer between Sputnik and the mimivirus can occur during the infection of Acanthamoeba. Therefore, it is hypothesized that the virophage could be a source of vehicle mediating lateral gene transfer between giant viruses, which constitute a significant part of the DNA virus
population in the marine environments. Moreover, the presence of three APMV genes in Sputnik implies that gene transfer between a virophage and a giant virus is crucial to viral evolution.
which preys on the giant Cafeteria roenbergensis virus
, and the Organic Lake virophage
, found in the salty Organic Lake
in Antarctica, and which preys on viruses that attack algae
. All host viruses of the known virophages belong to the group of nucleocytoplasmic large DNA viruses
.
Amoeba
Amoeba is a genus of Protozoa.History=The amoeba was first discovered by August Johann Rösel von Rosenhof in 1757. Early naturalists referred to Amoeba as the Proteus animalcule after the Greek god Proteus, who could change his shape...
cells that are already infected by a certain helper virus; Sputnik uses the helper virus's machinery for reproduction and inhibits replication of the helper virus.
Viruses like Sputnik that depend on co-infection of the host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
cell by helper viruses are known as satellite viruses
Satellite (biology)
A satellite is a subviral agent composed of nucleic acid that depends on the co-infection of a host cell with a helper or master virus for its multiplication. When a satellite encodes the coat protein in which its nucleic acid is encapsidated it is referred to as a satellite virus...
. At its discovery in a Paris water-cooling tower in 2008 Sputnik was the first known satellite virus that inhibited replication of its helper virus and thus acted as a parasite of that virus. In analogy to the term bacteriophage
Bacteriophage
A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...
it was called a virophage.
Virology
Sputnik virophage is icosahedralIcosahedron
In geometry, an icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is one of the five Platonic solids....
in shape and 50 nanometre
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
s in size. It has been found to multiply inside of Acanthamoeba
Acanthamoeba
Acanthamoeba is a genus of amoebae, one of the most common protozoa in soil, and also frequently found in fresh water and other habitats. The cells are small, usually 15 to 35 μm in length and oval to triangular in shape when moving. The pseudopods form a clear hemispherical lobe at the anterior,...
species, but only if that amoeba is infected with the large mamavirus
Mamavirus
Mamavirus is one of the most complex viruses discovered. It is a virus belonging to the family mimiviridae, which includes mimivirus, mamavirus, and marseillevirus The mimiviridae also belong to the family of the nucleocytoplasmic large DNA viruses , which includes the Poxviridae, the...
. Sputnik harnesses the mamavirus proteins to rapidly produce new copies of itself.
Mamavirus is formally known as Acanthamoeba polyphaga
Acanthamoeba
Acanthamoeba is a genus of amoebae, one of the most common protozoa in soil, and also frequently found in fresh water and other habitats. The cells are small, usually 15 to 35 μm in length and oval to triangular in shape when moving. The pseudopods form a clear hemispherical lobe at the anterior,...
mimivirus (APMV) and is a close relative of the previously known mimivirus
Mimivirus
Mimivirus is a viral genus containing a single identified species named Acanthamoeba polyphaga mimivirus , or is a group of phylogenetically related large viruses . In colloquial speech, APMV is more commonly referred to as just “mimivirus”...
. The mimivirus is a giant in the viral world; it has more genes than many bacteria and performs functions that normally occur only in cellular organisms. The mamavirus is even larger than the mimivirus, but the two are very similar in that they form large viral factories and complex viral particles. Virophage growth is deleterious to APMV and results in the production of abortive forms and abnormal capsid assembly of APMV. In one of the experiments done by inoculating Acanthamoeba polyphaga
Acanthamoeba
Acanthamoeba is a genus of amoebae, one of the most common protozoa in soil, and also frequently found in fresh water and other habitats. The cells are small, usually 15 to 35 μm in length and oval to triangular in shape when moving. The pseudopods form a clear hemispherical lobe at the anterior,...
with water containing an original strain of APMV, it was discovered that several capsid layers accumulate unsymmetrically on one side of the viral particle causing the virus to become ineffective. Sputnik decreased the yield of infective viral particle by 70% and also reduced the amoeba lysis by threefold at 24h.
Sputnik has a circular double stranded DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
consisting of 18,343 base pairs. It contains genes able to infect all three domains of life: Eukarya, Archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
and Bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
.
Of the twenty-one predicted protein-coding genes, three are apparently derived from APMV itself, one is a homologue of an archaeal virus, and four others are homologues of proteins in bacteriophages and eukaryotic viruses. Thirteen are ORFans
Orphan gene
An orphan gene is a gene that has limited phylogenetic distribution. In other words, there is no detectable homolog in other organisms or the homologous genes are restricted to closely related organisms....
, that is they do not have any detectable homologues in current sequence databases. The Sputnik genome has a high A + T content (73%) similar to that of APMV.
Several other homologues such as those of a primase–helicase, a packaging ATPase, an insertion sequence transposase DNA-binding subunit, and a Zn-ribbon protein, were detected in the Global Ocean Survey
Global Ocean Sampling Expedition
The Global Ocean Sampling Expedition is an ocean exploration genome project with the goal of assessing the genetic diversity in marine microbial communities and to understand their role in nature's fundamental processes. Begun as a Sargasso Sea pilot sampling project in August 2003, Craig Venter...
environmental data set, suggesting that virophages could be a currently unknown family of viruses.
Sputnik was found to contain genes that were shared by APMV. These genes could have been acquired by Sputnik after the association of APMV with the host and then interaction between the virophage and the viral host. Recombination within the viral factory might have resulted in the exchange of genes. Sputnik is one of the most convincing pieces of evidence for gene mixing and matching between viruses.
The presence of these genes homologous to the mimivirus in Sputnik suggests that gene transfer between Sputnik and the mimivirus can occur during the infection of Acanthamoeba. Therefore, it is hypothesized that the virophage could be a source of vehicle mediating lateral gene transfer between giant viruses, which constitute a significant part of the DNA virus
DNA virus
A DNA virus is a virus that has DNA as its genetic material and replicates using a DNA-dependent DNA polymerase. The nucleic acid is usually double-stranded DNA but may also be single-stranded DNA . DNA viruses belong to either Group I or Group II of the Baltimore classification system for viruses...
population in the marine environments. Moreover, the presence of three APMV genes in Sputnik implies that gene transfer between a virophage and a giant virus is crucial to viral evolution.
Other viruses
In March 2011, two additional virophages were described: the Mavirus virophageMavirus virophage
Mavirus virophage is a double stranded DNA virus that infects the marine phagotropic flagellate Cafeteria roenbergensis in the presence of a second virus - Cafeteria roenbergensis virus.The name is derived from Maverick virus....
which preys on the giant Cafeteria roenbergensis virus
Cafeteria roenbergensis virus
Cafeteria roenbergensis virus is a giant virus that infects the marine zooplankton Cafeteria roenbergensis . CroV has the largest genome of any known marine virus, consisting of ~730,000 base pairs of double-stranded DNA...
, and the Organic Lake virophage
Organic Lake virophage
Organic Lake virophage is a double stranded DNA virophage...
, found in the salty Organic Lake
Organic Lake
Organic Lake is a lake in the Vestfold Hills in eastern Antarctica. It was formed 6,000 years ago when sea levels were higher; it is isolated, rather shallow , meromictic, a few hundred meters in diameter and has extremely salty water...
in Antarctica, and which preys on viruses that attack algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
. All host viruses of the known virophages belong to the group of nucleocytoplasmic large DNA viruses
Nucleocytoplasmic large DNA viruses
The nucleocytoplasmic large DNA viruses or NCLDV refers to a number of families of large eukaryotic DNA viruses:# Asfarviridae# Iridoviridae# Marseilleviridae# Megaviridae# Mimiviridae# Phycodnaviridae# Poxviridae...
.