|Group:||Group I (dsDNA)|
Phycodnaviruses (members of the family Phycodnaviridae) are large (160 to 560 thousand base pairs), double stranded DNA viruses that infect marine or freshwater eukaryotic algae. They belong to a super-group of large viruses known as nucleocytoplasmic large DNA viruses (NCLDVs).
Phycodnaviruses have icosahedral morphology, an internal lipid membrane and replicate, completely or partly, in the cytoplasm of their host cells. The genomes range in size from 100 kilobases (kb) to >550 kb with G+C content between 40% and 50%.
The taxonomy of this family was initially based on the host range: Chlorovirus infect chlorella-like green algae from terrestrial waters, whereas members of the other five genera (Coccolithovirus, Phaeovirus, Prasinovirus, Prymnesiovirus and Raphidovirus) infect marine green and brown algae. This was subsequently confirmed by analysis of their DNA polymerases.
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 of the Phycodnaviruses encode a number of proteins involved in DNA replication or recombination, including a DNA-directed DNA polymerase. It is unclear if any of the Phycodnaviruses encode a fully functional replication machinery, however. They are thought to rely on host enzymes at least partially.
Until recently Phycodnaviruses were believed to infect algal species exclusively. Recently, DNA homologous to Chlorovirus Acanthocystis turfacea virus 1 (ATCV-1) was isolated from human nasopharyngeal mucosal surfaces. The presence of ATCV-1 in the human microbiome was associated with diminished performance on cognitive assessments. Innoculation 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.
- Anonymous (2012) Virus Taxonomy: IXth report of the international committee on taxonomy of viruses. Amsterdam: Academic Press p261
- 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. 2014 Oct 27. pii: 201418895. [Epub ahead of print]
- Wilson WH, Van Etten JL, Allen MJ (2009) The Phycodnaviridae: the story of how tiny giants rule the world. Curr Top Microbiol Immunol 328:1-42
- Van Etten JL. Unusual life style of giant chlorella viruses. Annu Rev Genet. 2003;37:153-95. Review. PMID 14616059 Open Access version
- Van Etten JL, Meints RH. Giant viruses infecting algae. Annu Rev Microbiol. 1999;53:447-94. Review. PMID 10547698 Open Access version
- Iyer LM, Balaji S, Koonin EV, Aravind L. Evolutionary genomics of nucleo-cytoplasmic large DNA viruses. Virus Reseearch. 2006 Apr;117(1):156-84. PMID 16494962
- Raoult D, Audic S, Robert C, Abergel C, Renesto P, Ogata H, La Scola B, Suzan M, Claverie JM. The 1.2-megabase genome sequence of Mimivirus. Science. 2004 Nov 19;306(5700):1344-50. doi:10.1126/science.1101485 PMID 15486256
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