Phycodnaviridae

Phycodnaviridae
Virus classification
Group: Group I (dsDNA)
Family: Phycodnaviridae
Genera

Phycodnaviridae is a family of large (100-560kb) double stranded DNA viruses that infect marine or freshwater eukaryotic algae. There are currently 33 species in this family, divided among 6 genera.[1][2] This family belongs to a super-group of large viruses known as nucleocytoplasmic large DNA viruses (NCLDVs).

Taxonomy

Group: dsDNA

[2]

The taxonomy of this family was initially based on the host range: chloroviruses infect chlorella-like green algae from terrestrial waters, whereas members of the other five genera infect marine green and brown algae. This was subsequently confirmed by analysis of their DNA polymerases.[3]

Structure

Viruses in Phycodnaviridae are enveloped, with icosahedral and round geometries, and T=169 symmetry. The diameter is around 100-220 nm.[1] They have an internal lipid membrane and replicate, completely or partly, in the cytoplasm of their host cells.

Genomes are linear, around 100-560kb in length. The genome has 700 open reading frames,[1] with G+C content between 40% and 50%.

Genus Structure Symmetry Capsid Genomic Arrangement Genomic Segmentation
RaphidovirusIcosahedralT=169EnvelopedLinearMonopartite
CoccolithovirusIcosahedralT=169EnvelopedLinearMonopartite
PhaeovirusIcosahedralT=169EnvelopedLinearMonopartite
ChlorovirusIcosahedralT=169EnvelopedLinearMonopartite
PrymnesiovirusIcosahedralT=169EnvelopedLinearMonopartite
PrasinovirusIcosahedralT=169EnvelopedLinearMonopartite

Life cycle

Viral replication is nucleo-cytoplasmic, and is lysogenic. Replication follows the DNA strand displacement model. DNA-templated transcription is the method of transcription. The virus exits the host cell by lysis via lytic phospholipids. Alga serve as the natural host. Transmission routes are passive diffusion.[1]

Genus Host Details Tissue Tropism Entry Details Release Details Replication Site Assembly Site Transmission
RaphidovirusAlgaNoneCell receptor endocytosisLysisNucleusCytoplasmPassive diffusion
CoccolithovirusAlgaNoneCell receptor endocytosisBuddingNucleusCytoplasmPassive diffusion
PhaeovirusAlgaNoneCell receptor endocytosisLysisNucleusCytoplasmPassive diffusion
ChlorovirusAlgaNoneCell receptor endocytosisLysisNucleusCytoplasmUnknown
PrymnesiovirusAlgaNoneCell receptor endocytosisLysisNucleusCytoplasmPassive diffusion
PrasinovirusAlgaNoneCell receptor endocytosisLysisNucleusCytoplasmPassive diffusion

Molecular biology

Recent studies have revealed features in Phycodnavirus genomes such as sophisticated replication and transcription machineries, a novel type of potassium channel protein, genes involved in inducing apoptosis in the host genome, a sophisticated signal transduction and gene regulation system and genes for glycosylation of viral proteins.

All phycodnaviruses encode a number of proteins involved in DNA replication or recombination, including a DNA-directed DNA polymerase. It is unclear if any phycodnaviruses encode a fully functional replication machinery, however. They are thought to rely on host enzymes at least partially.

Pathology

Until recently phycodnaviruses were believed to infect algal species exclusively. Recently, DNA homologous to Chlorovirus Acanthocystis turfacea virus 1 (ATCV-1) were isolated from human nasopharyngeal mucosal surfaces. The presence of ATCV-1 in the human microbiome was associated with diminished performance on cognitive assessments. Inoculation of ATCV-1 in experimental animals was associated with decreased performance in memory and sensory-motor gating, as well as altered expression of genes in the hippocampus related to synaptic plasticity, learning, memory formation, and the viral immune response.[4]

Evolution

Phycodnaviruses are a diverse collection of viruses with similar particles, which, although they have about 1000 genes, share only 13 of them between viruses in different genera.[5]

References

  1. 1 2 3 4 "Viral Zone". ExPASy. Retrieved 15 June 2015.
  2. 1 2 ICTV. "Virus Taxonomy: 2014 Release". Retrieved 15 June 2015.
  3. ↑ Anonymous (2012) Virus Taxonomy: IXth report of the international committee on taxonomy of viruses. Amsterdam: Academic Press p261
  4. ↑ Yolken, RH; et al. (2014). "Chlorovirus ATCV-1 is part of the human oropharyngeal virome and is associated with changes in cognitive functions in humans and mice". Proc Natl Acad Sci U S A. 111: 16106–16111. doi:10.1073/pnas.1418895111.
  5. ↑ genera

Additional reading

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