The RNA-packaged procapsid (protein shell) of "Pseudomonas phage phi6"
The RNA-packaged procapsid (protein shell) of Pseudomonas phage phi6
Virus classification e
(unranked): Virus
Realm: Riboviria
Phylum: incertae sedis
Family: Cystoviridae
Genus: Cystovirus

Cystovirus is a genus of viruses, in the family Cystoviridae.[1] Pseudomonas syringae pathovar phaseolicola bacteria serve as natural hosts. There is currently only one species in this genus: the type species Pseudomonas phage phi6.[1][2][3]


Group: dsRNA



Cystoviruses[1] are distinguished by their tripartite dsRNA genome, totaling ~14 kb in length and their protein and lipid outer layer. No other bacteriophage has any lipid in its outer coat, though the Tectiviridae and the Corticoviridae have lipids within their capsids.

Most identified cystoviruses infect Pseudomonas species, but this is likely biased due to the method of screening and enrichment.[4] The type species is Pseudomonas phage phi6, but there are many other proposed members of this family. Pseudomonas phage φ7, φ8, φ9, φ10, φ11, φ12, and φ13 have been identified and named,[5] but other cystovirus-like viruses have also been isolated.[4] These seven putative relatives are classified as either close (φ7, φ9, φ10, φ11) or distant (φ8, φ12, φ13) relatives to φ6,[5] with the distant relatives thought to infect via the LPS rather than the pili.[6]

Members of the Cystoviridae appear to be most closely related to the Reoviridae,[7] but also share homology with the Totiviridae. In particular, the structural genes of cystoviruses are highly-similar to those used by a number of dsRNA viruses that infect eukaryotes.[8]


Viruses included in the genus Cystovirus are enveloped, with icosahedral and Spherical geometries, and T=13, T=2 symmetry. The diameter is around 85 nm. Genomes are linear and segmented, and labeled as large (L) 6.4kb, Medium (M) 4 kb and Small (S) 2.9 kb in length. The genome codes for 12 proteins.[1][2]

Genus Structure Symmetry Capsid Genomic arrangement Genomic segmentation
Cystovirus Icosahedral T=13 laevo, T=2 Enveloped Linear Segmented

Life cycle[edit]

Viral replication is cytoplasmic. Replication follows the double-stranded RNA virus replication model. Double-stranded rna virus transcription is the method of transcription. Pseudomonas bacteria serve as the natural host.[1][2]

Genus Host details Tissue tropism Entry details Release details Replication site Assembly site Transmission
Cystovirus Bacteria: Pseudomonas None Pilus adsorption; membrane fusion Cell division; sporogenesis; cell fusion Cytoplasm Cytoplasm Unknown


Pseudomonas phage phi6 was the first virus in this family to be discovered and was initially characterized in 1973 by Anne K. Vidaver in the Department of Plant Pathology at the University of Nebraska. 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.[9]

In 1999, phi7-14 were identified by the laboratory of Leonard Mindich in the Department of Microbiology at the Public Health Research Institute associated with New York University. They did this by culturing various leaves in Lysogeny Broth and then plating the broth on lawns of Pseudomonas syringae pv phaseolicola. They were able to identify viral plaques from this and then subsequently sequence their genomes.[5]


  1. ^ a b c d e f "ICTV Report Cystoviridae".
  2. ^ a b c "Viral Zone". ExPASy. Retrieved 15 June 2015.
  3. ^ "NCBI Taxonomy Browser: Cystoviridae". NCBI. Retrieved 19 June 2016.
  4. ^ a b Silander OK, Weinreich DM, Wright KM, et al. (December 2005). "Widespread genetic exchange among terrestrial bacteriophages". Proc. Natl. Acad. Sci. U.S.A. 102 (52): 19009–14. Bibcode:2005PNAS..10219009S. doi:10.1073/pnas.0503074102. PMC 1323146. PMID 16365305.
  5. ^ a b c Mindich L, Qiao X, Qiao J, Onodera S, Romantschuk M, Hoogstraten D (August 1999). "Isolation of additional bacteriophages with genomes of segmented double-stranded RNA". J. Bacteriol. 181 (15): 4505–8. PMC 103579. PMID 10419946.
  6. ^ Gottlieb P, Potgieter C, Wei H, and Toporovsky I (2002). "Characterization of φ12, a Bacteriophage Related to φ6: Nucleotide Sequence of the Large Double-Stranded RNA". Virology. 295 (2): 266–271. doi:10.1006/viro.2002.1436. PMID 12033785.
  7. ^ Butcher SJ, Dokland T, Ojala PM, Bamford DH, Fuller SD (July 1997). "Intermediates in the assembly pathway of the double-stranded RNA virus phi6". EMBO J. 16 (14): 4477–87. doi:10.1093/emboj/16.14.4477. PMC 1170074. PMID 9250692.
  8. ^ Koonin, Eugene V.; Dolja, Valerian V.; Krupovic, Mart (2015). "Origins and evolution of viruses of eukaryotes: The ultimate modularity". Virology. 479-480: 2–25. doi:10.1016/j.virol.2015.02.039. PMC 5898234. PMID 25771806.
  9. ^ Vidaver AK, Koski RK, Van Etten JL (May 1973). "Bacteriophage Φ6 a Lipid-Containing Virus of Pseudomonas phaseolicola". Journal of Virology. 11 (15): 799–805.

External links[edit]