Bracovirus is a genus of viruses, in the family Polydnaviridae. Bracoviruses are an ancient symbiotic virus contained in parasitic braconid wasps that evolved from the nudivirus approximately 190 million years ago and has been evolving for at least 100 million years. It is one of two genera belonging to the Polydnaviridae family, with Ichnovirus being the other genus. There are 32 species in this genus.
Symbiosis Parasitoid wasps in the subfamilies Microgastrinae, Miracinae, Cheloninae, Cardiochilinae, Khoikhoiinae, and Mendesellinae 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. 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.
Taxonomy The genus Bracovirus contained the 32 species in ICTV versions 1999a-2020 The genus Bracoviriform contains the following 31 species starting ICTV version 2021 The species Ichnoviriform rostralis, previously known as Tranosema rostrale bracovirus was moved to Ichnoviriform (Ichnovirus) from Bracoviriform (Bracovirus) in 2021. Species Previous name,Virus name Abbreviation Bracoviriform altitudinis Chelonus altitudinis bracovirus CalBV Bracoviriform argentifrontis Ascogaster argentifrons bracovirus AaBV Bracoviriform blackburni Chelonus blackburni bracovirus CbBV Bracoviriform canadense Hypomicrogaster canadensis bracovirus HcBV Bracoviriform congregatae Cotesia congregata bracovirus CcBV Bracoviriform crassicornis Apanteles crassicornis bracovirus AcBV Bracoviriform croceipedis Microplitis croceipes bracovirus McBV Bracoviriform curvimaculati Chelonus nr. curvimaculatus bracovirus CcBV Bracoviriform demolitoris Microplitis demolitor bracovirus MdBV Bracoviriform ectdytolophae Hypomicrogaster ectdytolophae bracovirus HcEV Bracoviriform facetosae Diolcogaster facetosa bracovirus DfBV Bracoviriform flavicoxis Glyptapanteles flavicoxis bracovirus GflBV Bracoviriform flavipedis Cotesia flavipes bracovirus CfBV Bracoviriform flavitestaceae Phanerotoma flavitestacea bracovirus PfBV Bracoviriform fumiferanae Apanteles fumiferanae bracovirus AfBV Bracoviriform glomeratae Cotesia glomerata bracovirus CgBV Bracoviriform hyphantriae Cotesia hyphantriae bracovirus ChBV Bracoviriform inaniti Chelonus inanitus bracovirus CinaBV Bracoviriform indiense Glyptapanteles indiensis bracovirus GiBV Bracoviriform insularis Chelonus insularis bracovirus CinsBV Bracoviriform kariyai Cotesia kariyai bracovirus CkBV Bracoviriform liparidis Glyptapanteles liparidis bracovirus GlBV Bracoviriform marginiventris Cotesia marginiventris bracovirus CmaBV Bracoviriform melanoscelae Cotesia melanoscela bracovirus CmeBV Bracoviriform nigricipitis Cardiochiles nigriceps bracovirus CnBV Bracoviriform ornigis Pholetesor ornigis bracovirus PoBV Bracoviriform paleacritae Protapanteles paleacritae bracovirus PpBV Bracoviriform quadridentatae Ascogaster quadridentata bracovirus AqBV Bracoviriform rubeculae Cotesia rubecula bracovirus CrBV Bracoviriform schaeferi Cotesia schaeferi bracovirus CsBV Bracoviriform texani Chelonus texanus bracovirus CtBV
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.
Genus Structure Symmetry Capsid Genomic arrangement Genomic segmentationBracovirusProlate ellipsoidEnvelopedCircularSegmented
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.
The replication of the Bracoviriform 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 Bracoviriform shows head-to-head and tail-to-tail sequences, which is unexpected, given that it has evolved from the nudivirus The research conducted on Cotesia congregata shows that the viral genome contains one to three proviral segments.
The virus like particle 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 inhibiting the pupating of the host. The arresting of the host increases the chance of success of the wasp larva developing successfully.
Genus Host details Tissue tropism Entry details Release details Replication site Assembly site TransmissionBracoviriformParasitoid wasps (Braconidae)Hemocytes; fat bodiesUnknownLysis; buddingNucleusNucleusUnknown
References
External links Viralzone: Bracovirus ICTV