''Phikzvirus'' (synonym: ''PhiKZ-like viruses'', ''Phikzlikevirus'' before 2015) is a genus of viruses in the order '' Caudovirales'', in the family '' Myoviridae''. Bacteria serve as natural hosts. There are three species in this genus. Phages in this genus are considered large or "jumbo" phages. Three phages in this genus (φKZ, φPA3, and 201φ2-1) are known to assemble a "phage nucleus" structure similar in function to the eukaryotic

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

that encloses DNA as well as replication and transcription machinery. These structures are built from a tubulin-like ''PhuZ'' protein and a ''gp105'' shell protein. It provides immunity to host defenses like restriction enzymes and

CRISPR CRISPR () (an acronym for clustered regularly interspaced short palindromic repeats) is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea. These sequences are derived from DNA fragments of bacte ...

-Cas systems.

Taxonomy

The following three species are assigned to the genus: * ''

Pseudomonas virus PA7 ''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 ...

'' * ''

Pseudomonas virus phiKZ ''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 ...

'' * ''

Pseudomonas virus SL2 ''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 ...

Structure

Phikzviruses are

nonenveloped A viral envelope is the outermost layer of many types of viruses. It protects the genetic material in their life cycle when traveling between host cells. Not all viruses have envelopes. Numerous human pathogenic viruses in circulation are encase ...

, with a head and tail. The head has icosahedral symmetry (T=27), with a relatively large diameter of about 140 nm. The tail is around 160 nm long, 35 nm wide.

Genome

Genomes are circular, around 280kb in length. Two of the three species have been fully sequenced and are available from ICTV. They range between 211k and 280k nucleotides, with 201 to 306 proteins. The complete genomes, along with one other similar but unclassified genome, are availabl
here

Life cycle

Viral replication is cytoplasmic. The virus attaches to the host cell using its terminal fibers, and ejects the viral DNA into the host cytoplasm via contraction of its tail sheath. DNA-templated transcription is the method of transcription. Once the viral genes have been replicated, the procapsid is assembled and packed. The tail is then assembled and the mature virions are released via lysis. Bacteria serve as the natural host. Transmission routes are passive diffusion.

History

According to the ICTV's 2009 report, the genus ''PhiKZ-like viruses'' was first accepted as a new genus, at the same time as all three of its contained species. This proposal is availabl
here
In 2012, the name was changed to ''Phikzlikevirus''. This proposal is availabl
here
The genus was later renamed ''Phikzvirus''.

References

External links

ICTV
{{Use dmy dates, date=April 2017 Myoviridae Virus genera