Bidensovirus Explained

Bidensovirus is a genus of single stranded DNA viruses that infect invertebrates. The species in this genus were originally classified in the family Parvoviridae (subfamily Densovirinae) but were moved to a new genus because of significant differences in the genomes.^[1]

Taxonomy

There is one species in this genus currently recognised: Bombyx mori bidensovirus.

Host

As the name suggests this virus infects Bombyx mori, the silkworm.^[2]

Virology

The virions are icosahedral, non enveloped and ~25 nanometers in diameter. They contain two structural proteins.

The genome is bipartite, unique among ssDNA viruses, with two linear segments of ~6 and 6.5 kilobases (kb). These segments and the complementary strands are that are packaged separately giving rise to 4 different types of full particles.

Both segments have an ambisense organization, coding for a structural protein in one sense and the non-structural proteins on the complementary strand.

• DNA1 (also known as VD1) — the larger segment of 6.5 kb — encodes the capsid protein VP1 (128 kDa — kilodaltons) on one strand and three non-structural proteins — NS1 of 14 kDa, NS2 of 37 kDa and NS3 of 55 kDa — on the complementary strand.
• DNA2 (also known as VD2) — the smaller segment of 6 kb — encodes the capsid protein VP2 (133 kDa) on one strand and the non-structural protein NS4 (27 kDa) on the complementary strand.

The open reading frame 4 (VD1-ORF4) is 3318 nucleotides (bases) in length and encodes a predicted 1105 amino acid protein which has a conserved DNA polymerase motif. It appears to encode at least 2 other proteins including one of ~53 kDa that forms part of the virion.^[3]

Evolution

Comprehensive analysis of bidnavirus genes has shown that these viruses have evolved from a parvovirus ancestor from which they inherit a jelly-roll capsid protein and a superfamily 3 helicase.^[4] It has been further suggested that the key event that led to the separation of the bidnaviruses from parvoviruses was the acquisition of the PolB gene. A likely scenario has been proposed under which the ancestral parvovirus genome was integrated into a large virus-derived DNA transposon of the Polinton/Maverick family (polintoviruses) ^[5] resulting in the acquisition of the polintovirus PolB gene along with terminal inverted repeats. Bidnavirus genes for a minor structural protein (putative receptor-binding protein) and a potential novel antiviral defense modulator were derived from dsRNA viruses (Reoviridae) and dsDNA viruses (Baculoviridae), respectively.

External links

• Bidensovirus ~ ViralZone page. The top image erraneously shows a monopartite genome, text and genome map are right (March 30, 2021).

Notes and References

1. Virus Taxonomy: Ninth Report of the International Committee on Taxonomy of Viruses (2011)
2. Web site: Bidensovirus ~ ViralZone page .
3. 10.1007/s00284-013-0306-9 . Li G, Hu Z, Guo X, Li G, Tang Q, Wang P, Chen K, Yao Q Identification of Bombyx mori Bidensovirus VD1-ORF4 Reveals a Novel Protein Associated with Viral Structural Component. Curr Microbiol 66, 527–534 (2013). . Current Microbiology . June 2013 . 66 . 6 . 527–534 . Li . Guohui . Hu . Zhaoyang . Guo . Xuli . Li . Guangtian . Tang . Qi . Wang . Peng . Chen . Keping . Yao . Qin . 23328902 . 15920465 .
4. Krupovic M, Koonin EV. Evolution of eukaryotic single-stranded DNA viruses of the Bidnaviridae family from genes of four other groups of widely different viruses. Sci Rep. 2014. 4. 5347. 10.1038/srep05347. 24939392. 4061559.
5. Krupovic M, Bamford DH, Koonin EV. Conservation of major and minor jelly-roll capsid proteins in Polinton (Maverick) transposons suggests that they are bona fide viruses. Biol Direct. 2014. 9. 1. 6. 10.1186/1745-6150-9-6. 24773695. 4028283 . free .