Keeping up with virus taxonomy: rod-shaped viruses, cancer-associated viruses and viruses that infect archaea
Posted on October 15, 2019 by Laura Cox
Continuing the ‘Keeping up with virus taxonomy’ blog series, in this post we look at the viruses that infect archaea that thrive in some of the most hostile environments on Earth, viruses that keep crop pest populations under control and a virus that has been linked to cancer in raccoons.
Clavaviridae
Viruses in the family Clavaviridae replicate in hyperthermophilic archaea from the Aeropryum genus. There is currently only one species in the Clavaviridae family, called Aeropyrum pernix bacilliform virus 1. The archaeon this virus infects is usually found near underwater thermal vents and thrives in salty conditions and temperatures of 90–95°C. The virus infects Aeropyrum pernix chronically, using its cellular machinery to reproduce but leaving the cell intact.
The virus is not only unique genetically, but also in shape. Aeropyrum pernix bacilliform virus 1 are rod-shaped, narrow and long (just 16 nanometres wide and 143 nanometres in length) with one pointed end and a rounded tip.
3D model of Aeropyrum pernic bacilliform virus 1
Guttaviridae
Geothermal fields near
Steaming Hill, New Zealand
Clavaviruses
aren’t the only family of virus that infect heat-loving archaea. Viruses in the Guttaviridae family infect hyperthermophiles in the phylum Crenarchaeota. Unlike the long and narrow Aeropyrum pernix bacilliform virus 1, viruses in Guttaviridae are droplet-shaped or round structures, that are unprecedented in viruses that infect bacteria and eukaryotes.
There are two species within Guttaviridae, both within a distinct genus: Sulfolobus newzealandicus droplet-shaped virus (SNDV) and Aeropyrum pernix ovoid virus 1 (APOV1). Both viruses were found in archaea that thrive in extremely hot, sulphuric environments. APOV1 was discovered embedded within the genome of an archaea living near to a volcanic vent in Japan and SNDV was found in a field sample collected from Steaming Hill, New Zealand.
Ascoviridae
Viruses in the Ascoviridae family infect the larvae of certain insects, including butterflies and moths. These viruses are ecologically important as they keep populations of many insect pests low. This family of virus contains two genera; Ascovirus and Toursvirus. Ascoviruses are spread by wasps to caterpillars and Toursviruses infect the tropical ermine moth, which is a minor agriculture pest.
Polyomaviridae
Polyomaviruses are small, round and have been found to cause diseases in mammals, birds and fish. The Polyomaviridae family is large, containing four genera – Alpha-, Beta-, Gamma- and Deltapolyomavirus – within which there are over 70 different species:
- Viruses in the Alphapolyomavirus genus – of which there are over thirty – infect mammals, including people. Two alphapolyomaviruses cause cancer: Merkel cell polyomavirus, which causes skin cancer in people and raccoon polyomavirus, which affects raccoons.
- The twenty-plus viruses in the genus Betapolyomavirus also infect mammals, and can cause severe diseases, including kidney disease and damage to the white matter of the brain, called leukoencephalopathy.
- Gammapolyomaviruses infect birds and cause often fatal infections. There are fewer than ten polyomaviruses in this genus.
- Some of the viruses in the genus Deltapolyomavirus exist as part of the normal skin and gut microflora in humans, but in people who are immunocompromised, these viruses can cause a rash.
The International Committee on Taxonomy of Viruses (ICTV) is responsible for developing and maintaining a universal virus taxonomy. Known viruses are categorised into a classification scheme, taking into consideration their physical and biological properties in combination with their phylogenetic relationships.
Thanks to funding from the Wellcome Trust, two-page summaries of each chapter of the ICTV report (a free resource published by the ICTV which provides an up-to-date description of virus taxonomy) are available for free in the Journal of General Virology. These summaries are known as ICTV Virus Taxonomy Profiles and describe the structure, replication and taxonomy of each virus order and family.