Viruses of the Archaea


Viruses infecting members of Archaea, the third domain of life, constitute an integral, yet unique part of the virosphere. Many of these viruses, specifically the species that infect hyperthermophilic hosts, display morphotypes – for example, bottle shaped, spindle shaped, droplet shaped, coil shaped, bacilliform – not known to be associated with the other two cellular domains, Bacteria and Eukarya. The distinctiveness of the hyperthermophilic archaeal viruses extends to their genome sequences: a large majority of the predicted genes yield no sequence matches in public databases and encode proteins with exceptional structures and unknown functions. Moreover, the ways in which these viruses interact with their hosts are also unique, as indicated by a unique virion egress mechanism, which involves formation of pyramidal portals on the cell surface. Some viruses that infect extremely halophilic Archaea are morphologically highly similar to head‐tail bacterial viruses of the order Caudovirales and apparently share an ancestry with them. Identified archaeal viruses almost exclusively carry double‐stranded deoxyribonucleic acid (DNA) genomes and only a few species have single‐stranded DNA genomes.

Key Concepts

  • Archaea, the third domain of life, same as the two other domains, Bacteria and Eukarya, is parasitised by viruses.
  • Known species of archaeal viruses have been isolated from environments with extreme conditions – extremely high temperatures, exceeding 80 °C, or extremely high salinity.
  • Known archaeal viruses have DNA genomes, most of which are double stranded.
  • Morphological diversity of archaeal viruses exceeds that of bacterial viruses (bacteriophages).
  • Archaeal viruses from extreme thermal environments are enveloped and have diverse unusual morphologies, indicative of multiple independent origins.
  • Most known viruses from highly saline waters resemble bacteriophages and share an ancestry with them.
  • Most of the genes of hyperthermophilic archaeal viruses have no homologues in other known viruses.
  • The knowledge on viruses of Archaea contributes to the understanding of the origin and evolution of viruses and virus–host interactions.

Keywords: Archaea; DNA virus; viru; virion structure; hyperthermophile; extreme halophiel; virus evolution; biodiversity

Figure 1. Electron micrographs of viruses of the Archaea. (a) Sulfolobus islandicus rod‐shaped virus 1, SIRV1. (b) Acidianus filamentous virus 1, AFV1; in insets claw‐like structures are shown in ‘open’ and ‘closed’ conformation; white arrow indicates a ‘claw’ clamped around host pili and separated from the virion body, and black arrow indicates pili‐like appendices of the host cell. (c) Sulfolobus shibatae virus 1, SSV1. (d) Acidianus two‐tailed virus, ATV. (e) Sulfolobus neozealandicus droplet‐shaped virus, SNDV. (f) Acidianus bottle‐shaped virus, ABV. (g) Pyrobaculum spherical virus, PSV and (h) Haloarchaeal virus phiH. Scale bars represent 200 nm except in (g), (h), (i) and insets where it represents 100 nm. Figures (a), (c), (e) and (i) are courtesy of the late Wolfram Zillig. (b) Reproduced from Bettstetter et al.2003, Virology 315, 68–79 © Elsevier. (f) Reproduced from Haring et al. 2005a © the American Society for Microbiology. (g) Reproduced from Haring et al.2004 © Elsevier.
Figure 2. Proportions of different sets of genes in genomes of archaeal viruses. Viral + Cell, genes with homologues in other viruses and cellular life forms; viral only, genes with homologues detectable only in other viruses; cellular, genes with homologues detectable only in cellular life forms; unique, genes without detectable homologues. Reproduced from Prangishvili et al.2006 © Elsevier.


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Further Reading

Atanasova NS, Bamford DH and Oksanen H (2015a) Haloarchaeaal virus morphotypes. Biochimie 118: 333–343.

Atanasova NS, Senčilo A, Pietilä MK, et al. (2015b) Comparison of lipid‐containing bacterial and archaeal viruses. Advances in Virus Research 92: 1–61.

Dellas N, Snyder JC, Bolduc B and Young MJ (2014) Archaeal viruses: diversity, replication, and structure. Annual Review of Virology 1: 399–425.

Dyall‐Smith M and Porter K (2015) A strange family, or how a new pleolipovirus reveals its friends and relatives. Molecular Microbiology 98: 995–997.

Krupovic M, White MF, Forterre P and Prangishvili D (2012) Postcards from the edge: structural genomics of Archaeal viruses. Advances in Virus Research 82: 51–81.

Prangishvili D (2013) The wonderful world of archaeal viruses. Annual Review of Microbiology 67: 565–585.

Prangishvili D (2015) Living fossils of the ancient virosphere? Annals of the New York Academy of Sciences 1341: 35–40.

Stedman KM, DeYoung M, Saha M, et al. (2015) Structural insights into the architecture of the hyperthermophilic fusellovirus SSV1. Virology 474: 105–109.

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Prangishvili, David, Basta, Tamara, Garrett, Roger A, and Krupovic, Mart(Aug 2016) Viruses of the Archaea. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000774.pub3]