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Virus classification
Group: Group I (dsDNA)
Order: Unassigned
Family: Phycodnaviridae

Phycodnaviridae is a family of 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: 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.[1]

Molecular biology[edit]

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.


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.[2]


Phycodnaviruses of viruses evolved from the Iridoviridae family of viruses.[3]


  1. ^ Anonymous (2012) Virus Taxonomy: IXth report of the international committee on taxonomy of viruses. Amsterdam: Academic Press p261
  2. ^ 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]
  3. ^ 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

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