Giant virus

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As a giant Virus ( English virus giant , GM, or shortly Girus ) are very big referred viruses. Although the exact criteria vary in the scientific literature, viruses with a large capsid of at least 200 to 400  nm , typically surrounded by a thick layer of filamentous protein fibers (thickness approx. 100 nm) , are generally referred to as giant viruses . This means that many giant viruses are larger than the average bacteria.

Electron microscope image of a virus particle of mimivirus (en. Mimicking microbe virus ) with clearly visible filamentous cover
Size comparison of some giant viruses with HIV and a bacterium ( E. Coli )

The lower limit for the genome size is usually set at 300  kbp (kilobase pairs; pairs , since all known giant viruses have a double- stranded DNA genome). However, Yutin and Koonin (2019) set a slightly higher limit of 500 kbp, as did Brandes and Linial (2019).

At the upper end, genomes with 1000 kbp and more were found, for example with “ Tupan virus ” with 1,516 kbp.

The genome of the giant virus encompasses an order of magnitude of around 1000 coding genes (instead of hardly a dozen otherwise). This is extremely extensive compared to other virus genomes.

The late discovery of most giant viruses (numerous not until around 2003) was due to the fact that they got stuck in the filters (with a typical pore size of 0.2 μm) during the search for viruses, which were supposed to separate bacteria and protists from viruses easily visible clumps aggregate and also multiply more slowly.

The known giant viruses belong to the dsDNA virus Phylum Nucleocytoviricota (obsolete Nucleocytoplasmic large DNA viruses , NCLDV), and although the classes Megaviricetes (u. A. The families mimiviridae and phycodnaviridae ) or the order Asfuvirales from the class Pokkesviricetes (with the genus Asfivirus , the causative agent of African swine fever ). The hosts of the giant viruses are complex-cellular organisms ( eukaryotes ).

Laurie O'Keefe gave a graphic representation of the proportions.

Giant phages

For large viruses from prokaryotes ( bacteria or archaea : phages ), separate size criteria have been created, since their hosts naturally do not offer that much space. Here, too, all known representatives are dsDNA viruses. For details, see giant phages, megaphages and jumbo phages .

Individual evidence

  1. ↑ Kelly A. Reynolds: Mysterious Microbe in Water Challenges the Very Definition of a Virus . In: Water Conditioning & Purification . 2010. (via web archive from March 19, 2014)
  2. ↑ Ogata H, Toyoda K, Tomaru Y, Nakayama N, Shirai Y, Claverie JM, Nagasaki K: Remarkable sequence similarity between the dinoflagellate-infecting marine girus and the terrestrial pathogen African swine fever virus . In: Virology Journal . 6, No. 178, 2009-2010, p. 178. doi : 10.1186 / 1743-422X-6-178 . PMID 19860921 . PMC 2777158 (free full text).
  3. ↑ Eugene V. Koonin, Natalya Yutin: Evolution of the Large Nucleocytoplasmatic DNA Viruses of Eukaryotes and Convergent Origins of Viral Gigantism , in: Advances in Virus research, Volume 103, AP January 21, 2019, doi: 10.1016 / bs.aivir.2018.09 .002 , pp. 167-202. The toilet viruses are partially missed as toilet viruses.
  4. ↑ Nadav Brandes, Michal Linial: Giant Viruses - Big Surprises , in: Viruses 11 (5); 404 of April 30, 2019, doi: 10.3390 / v11050404 , PMC 6563228 (free full text), PMID 31052218
  5. ↑ a b James L. Van Etten, Leslie C. Lane, David D. Dunigan: DNA Viruses: The Really Big Ones (Giruses) . Annu. Rev. Microbiol. 64, 2010, pp. 83-99, doi: 10.1146 / annurev.micro.112408.134338 ( full text free for personal use ).
  6. ↑ James L. Van Etten: Giant Viruses . In: American Scientist . 99, No. 4, July-August 2011, pp. 304-311. doi : 10.1511 / 2011.91.304 . (via web archive from June 11, 2011)
  7. ↑ Legendre M, Arslan D, Abergel C, Claverie JM: Genomics of Megavirus and the elusive fourth domain of Life . In: Communicative & Integrative Biology . 5, No. 1, January 2012, pp. 102-106. doi : 10.4161 / cib.18624 . PMID 22482024 . PMC 3291303 (free full text).
  8. ↑ Laurie O'Keefe: Sizing Up Viruses , on: The Scientist. Illustration for Didier Raoult: Viruses Reconsidered , ibid 28 February 2014

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