''Cystovirus'' is a genus of

double-stranded RNA viruses Double-stranded RNA viruses (dsRNA viruses) are a Polyphyly, polyphyletic group of viruses that have Nucleic acid double helix, double-stranded genomes made of ribonucleic acid. The double-stranded genome is used to transcribe a Sense (molecular ...

which infects

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. It is the only genus in the family ''Cystoviridae.'' The name of the group c''ysto'' derives from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''kystis'' which means bladder or sack. There are seven species in this genus.

Discovery

'' Pseudomonas virus phi6'' was the first virus in this family to be discovered and was initially characterized in 1973 by Anne Vidaver at the

University of Nebraska A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, ...

. She found that when she cultured the bacterial strain '' Pseudomonas phaseolicola'' HB1OY with halo blight infected bean straw, cytopathic effects were detected in cultured lawns, indicating that there was a lytic microbe or bacteriophage present. In 1999, phi7–14 were identified by the laboratory of Leonard Mindich at the Public Health Research Institute associated with

New York University New York University (NYU) is a private research university in New York City. Chartered in 1831 by the New York State Legislature, NYU was founded by a group of New Yorkers led by then- Secretary of the Treasury Albert Gallatin. In 1832, th ...

. They did this by culturing various leaves in

Lysogeny Broth Lysogeny broth (LB) is a nutritionally rich medium primarily used for the growth of bacteria. Its creator, Giuseppe Bertani, intended LB to stand for lysogeny broth, but LB has also come to colloquially mean Luria broth, Lennox broth, life br ...

and then plating the broth on lawns of '' Pseudomonas syringae pv phaseolicola''. They were able to identify

viral plaque A viral plaque is a visible structure formed after introducing a viral sample to a cell culture grown on some nutrient medium. The virus will replicate and spread, generating regions of cell destruction known as plaques. For example, Vero cell or ...

s from this and then subsequently sequence their genomes.

Microbiology

Structure

Cystovirus particles are enveloped, with

icosahedral In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...

and spherical geometries, and T=13, T=2 symmetry. The virion diameter is around 85 nm. Cystoviruses are distinguished by their outer layer

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

and

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...

envelope. No other bacteriophage has any lipid in its outer coat, though the '' Tectiviridae'' and the '' Corticoviridae'' have lipids within their

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 ...

Genome

Cystoviruses have a tripartite double-stranded RNA genome which is approximately 14 kbp in total length. The genome is linear and segmented, and labeled as large (L) 6.4 kbp, medium (M) 4 kbp, and small (S) 2.9 kb in length. The genome codes for twelve proteins.

Life cycle

Cytoviruses enter the bacteria by adsorption on its

pilus A pilus (Latin for 'hair'; plural: ''pili'') is a hair-like appendage found on the surface of many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some r ...

and then membrane fusion. Viral replication is cytoplasmic. Replication follows the double-stranded RNA virus replication model. Double-stranded RNA virus transcription is the method of transcription. The progeny viruses are released from the cell by lysis. Most identified cystoviruses infect ''

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able t ...

'' species, but this is likely biased due to the method of screening and enrichment. There are many proposed members of this family. Pseudomonas viruses φ7, φ8, φ9, φ10, φ11, φ12, and φ13 have been identified and named, but other cystovirus-like viruses have also been isolated. These seven putative relatives are classified as either close (φ7, φ9, φ10, φ11) or distant (φ8, φ12, φ13) relatives to φ6, with the distant relatives thought to infect via the LPS rather than the pili. However, cystoviruses do not only infect ''Pseudomonas''. But also bacteria of the genera '' Streptomyces'',Siddharth R. Krishnamurthy, Andrew B. Janowski,Guoyan Zhao, Dan Barouch, David Wang (2016)
Hyperexpansion of RNA Bacteriophage Diversity
PlosOne. '' Microvirgula'',Xiaoyao Cai, Fengjuan Tian, Li Teng, Hongmei Liu, Yigang Tong Tong, Shuai Le, Tingting Zhang (2021)
Cultivation of a Lytic Double-Stranded RNA Bacteriophage Infecting Microvirgula aerodenitrificans Reveals a Mutualistic Parasitic Lifestyle
American Society for Microbiology. ''

Acinetobacter ''Acinetobacter'' is a genus of gram-negative bacteria belonging to the wider class of Gammaproteobacteria. ''Acinetobacter'' species are oxidase-negative, exhibit twitching motility, and occur in pairs under magnification. They are importan ...

'',Clay S. Crippen, Bibi Zhou, and Christine M. Szymanski (2021)
RNA and Sugars, Unique Properties of Bacteriophages Infecting Multidrug Resistant Acinetobacter radioresistens Strain LH6
NCBI. ''

Lactococcus ''Lactococcus'' is a genus of lactic acid bacteria that were formerly included in the genus ''Streptococcus'' Group N1. They are known as homofermenters meaning that they produce a single product, lactic acid in this case, as the major or only pr ...

'', '' Pectobacterium'',Cystoviridae
NCBI Taxonomy. and possibly other bacterial genera.

Taxonomy

Members of the ''Cystoviridae'' appear to be most closely related to the ''

Reoviridae ''Reoviridae'' is a family of double-stranded RNA viruses. Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi. They lack lipid envelopes and package their segmented genome within multi-layere ...

'', but also share homology with the ''

Totiviridae ''Totiviridae'' is a family of double-stranded RNA viruses. Giardia lamblia, leishmania, trichomonas vaginalis, and fungi serve as natural hosts. The name of the group derives from Latin ''toti'' which means undivided or whole. There are 28 spec ...

''. In particular, the structural genes of cystoviruses are highly-similar to those used by a number of dsRNA viruses that infect eukaryotes. The genus ''Cystovirus'' has seven species: * '' Pseudomonas virus phi6'' * '' Pseudomonas virus phi8'' * '' Pseudomonas virus phi12'' * '' Pseudomonas virus phi13'' * '' Pseudomonas virus phi2954'' * '' Pseudomonas virus phiNN'' * '' Pseudomonas virus phiYY'' Other unassigned phages: * '' Microvirgula virus phiNY'' * '' Streptomyces virus phi0'' * '' Lactococcus virus phi7-4'' * '' Pectobacterium virus MA14'' * '' Acinetobacter virus CAP3'' * '' Acinetobacter virus CAP4'' * '' Acinetobacter virus CAP5'' * '' Acinetobacter virus CAP6'' * '' Acinetobacter virus CAP7''

References

External links

ICTV Online Report: ''Cystoviridae''

{{Authority control Cystoviridae Riboviria Virus genera