Bracovirus

Bracovirus is a genus of viruses, in the family Polydnaviridae. Bracoviruses are an ancient symbiotic virus contained in parasitic braconid wasps that evolved off of the nudivirus about 190 million years ago and has been evolving at least 100 million years.^[1] It is one of two genera belonging to the Polydnaviridae family, Ichnovirus being the other genus. There are currently 32 species in this genus including the type species Cotesia melanoscela bracovirus.^[2][3]

Symbiosis

Parasitoid wasps are the natural hosts for Bracoviruses, though the virus does not cause disease in these wasps. Instead, the wasps are themselves parasites of lepidoptera. The wasp injects one or more eggs into its lepidoptera host along with a quantity of virus. The virus does not replicate inside the wasp's host, but expression of viral genes prevents its immune system from killing the wasp's egg and causes other physiological alterations that ultimately cause the parasitized host to die.^[2] Studies conducted on Cotesia congregata have shown that male wasps do contain proviral sequences of DNA, but the females are the ones responsible for the amplification of the viral DNA.^[4]

Taxonomy

Group: dsDNA

^[3]

Structure

Viruses in Bracovirus are enveloped, with prolate ellipsoid and Cylindrical geometries. Genomes are circular and segmented, around 2.0-31kb in length. The genome of the virus is enveloped with 35 double stranded DNA (dsDNA) all of which are circular.^[2][4]

Life cycle

Viral replication is nuclear. DNA templated transcription is the method of transcription. The virus exits the host cell by nuclear pore export. Transmission routes are parental.^[2]

The replication of the Bracovirus occurs within the ovaries of a parasitic wasps in calyx cells and is maintained by vertical transmission and to go into further detail the packaged genome of dsDNA is replicated inside of the wasp ovaries by development of the sequences of the virus from proviral segments in the tandem arrays in the wasp genome. The development of the sequences of bracovirus shows head-to-head and tail-to-tail sequences, which is unexpected, given that it has evolved from the nudivirus ^[4] The research conducted on Cortesia congregata shows that the viral genome contains one to three proviral segments.^[4]

The virus is transmitted into a lepidopteran host (a caterpillar) and infects and manipulates the physiology of the caterpillar so that it can be used as a living incubator for wasp larvae. When this happens the virus disrupts the caterpillar's immune system causing paralysis and inhibting the pupating of the host. The arresting of the host increases the chance of success of the wasp larva developing successfully.^[1]

^[2]

References

External links

• Viralzone: Bracovirus
• ICTV