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Virus classification
Group: Group III (dsRNA)
Family: Cystoviridae
Genus: Cystovirus

Cystovirus is a genus of dsRNA virus that infect certain Gram-negative bacteria.


All cystoviruses are distinguished by their three strands (analogous to chromosomes) of dsRNA, totalling ~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.[1] The type species is Pseudomonas phage Φ6, but there are many other members of this family. Φ7, Φ8, Φ9, Φ10, Φ11, Φ12, and Φ13 have been identified and named,[2] but other cystoviruses have also been isolated.[1]

Members of the Cystoviridae appear to be most closely related to the Reoviridae,[3] but also share homology with the Totiviridae. Cystoviruses are the only bacteriophage that are more closely related to viruses of eukaryotes than to other phage.


Φ6 was the first virus in this family to be discovered and was initially characterized in 1973 in James Van Etten's laboratory in the Department of Plant Pathology at the University of Nebraska. They found that when they cultured the bacterial strain Pseudomonas phaseolicola HB1OY with wild Pseudomonas phaseolicola from infected bean straw, there was cytopathic effect, implying that there was a lytic bacteriophage present in their wild Pseudomonas. [4]

In 1999, Φ7-14 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.[2]


  1. ^ 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. doi:10.1073/pnas.0503074102. PMC 1323146. PMID 16365305. 
  2. ^ a b 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. 
  3. ^ 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. 
  4. ^ 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. 

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