Bidensovirus


Bidensovirus is a genus of single stranded DNA viruses that infect invertebrates. The species in this genus were originally classified in the family Parvoviridae but were moved to a new genus because of significant differences in the genomes.

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.

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. 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 — the larger segment of 6.5 kb — encodes the capsid protein VP1 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 — the smaller segment of 6 kb — encodes the capsid protein VP2 on one strand and the non-structural protein NS4 on the complementary strand.
The open reading frame 4 is 3318 nucleotides 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.

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. 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 resulting in the acquisition of the polintovirus PolB gene along with terminal inverted repeats. Bidnavirus genes for a minor structural protein and a potential novel antiviral defense modulator were derived from dsRNA viruses and dsDNA viruses, respectively.