# Giant Viruses #### Yağmur ilayda DEMİR #### 1605A051 ---- ## CONTENTS ### Common Features of Giant Viruses ### Giant Virus Families ### *Mimiviridae* Family ### *Pithoviridae* Family ### *Pandoraviridae* Family ### *Phycodnaviridae* Family ### *Marseilleviridae* Family ### Uncharacterized Family ------ ### Common Features of Giant Viruses Although giant viruses are divided into different virus families, there are some common features between them: - All giant viruses have double-stranded DNA (dsDNA). - All giant viruses NCLDVs (Nucleocytoplasmic Large DNA Viruses) are superpositions. - The genome of giant viruses is larger than 288 Kbps. - Giant viruses enter the cell by phagocytosis.[1] ---- ### Giant Virus Families While giant viruses were newly discovered, they currently consist of five virus families: - *Mimiviridae* family - *Pithoviridae* family - *Pandoraviridae* family - *Phycodnaviridae* family - *Marseilleviridae* family - Uncharacterized family [1] ![](https://i.imgur.com/IDiTzBM.png) Table 1:Giant viruses.[1] ---- ### *Mimiviridae* Family - Group 1: dsDNA - The most well-known examples of this virus are Mamavirus and Mimivirus. - Virophage was discovered for the first time in this virus. - There are 8 types of virophages detected in this virus family. - 26 species belonging to this family. - They are transmitted by passive diffusion.[2] ![1](https://i.imgur.com/mAPpAZD.png) Mimivirus Star-Shaped Structures (A) TEM image of cryo-fixed sectioned and stained extracellular Mimivirus particles revealing a star-shaped structure at a unique vertex. (B) Cryo-TEM image of a whole vitrified fiber-less Mimivirus. (C) SEM image of the star-shaped structure in a mature extracellular Mimivirus particle. (D) Cryo-SEM of an immature, fiber-less particle. (E) Tomographic slice of a mature intracellular Mimivirus particle captured at a late (12 h post infection) infection stage. As shown in Video S1, at this late stage the host cell is packed with mature viral particles. (F and G) Volume reconstruction of the particle shown in (E), revealing the presence of an outer (red) and inner (orange) capsid shells. The star-shaped structure is present in both shells but adopts partially open (dark, star-like region), and completely sealed configurations in the outer and inner shells, respectively. (H) Superposition of the two shells in (F) and (G). Scale bars, 100 nm in (A, B, D, and E), and 200 nm in (C).[4] ---- ### *Pithoviridae* Family - Group 1: dsDNA - Two species belonging to this family have been identified. - The first specimen was found in the 30,000-year-old Siberian permafrost. - The capsid size they have is quite large compared to the genome size. - It has stripes consisting of an inner and an outer membrane with 15 nm spacing. - It enters the cell through phagocytosis.[2] ![2](https://i.imgur.com/4h4kU8D.jpg) J. BARTOLI and C. ABERGEL, The new mega-virus, Pithovirus sibericum (surrounded by a dark outer coating and viewed with two different methods) rests within the single-celled amoeba that it infected.[5] --- ### *Pandoraviridae* Family - Group 1: dsDNA - There are 3 identified species belonging to this virus family. - Pandoravirus salinus, which has the largest genome size (2450-2470 Kbp genome size), belongs to this family. - Capsid dimensions are large enough to be seen in a light microscope (500×1000 nm). - It enters the cell through phagocytosis. - After releasing its genetic material into the cell, it is distinguished from other families by disorganizing the nucleus of amoeba.[2] ![3](https://i.imgur.com/fCWwtpH.jpg) IGS CNRS-AMU, Pandoravirus salinus. --- ### *Phycodnaviridae* Family - Group 1: dsDNA - Members of this virus family are divided into genera according to the organism they infect. - They mostly infect eukaryotic algae and seaweeds. - They are transmitted by passive diffusion.[3] ![4](https://i.imgur.com/wIqpQgT.jpg) Phycodnaviridae. 2018.[7] --- ### *Marseilleviridae* Family - Group 1: dsDNA - 11 species belonging to this virus family have been identified. - No virophage species are belonging to this virus family. - They are transmitted through Diffusion in Water.[2] ![5](https://i.imgur.com/K06pAdz.jpg) Images of cryo-frozen Marseilleviridae particles (left and center) and enlarged diagram of structure near a vertex. Black arrows indicate Large Dense Bodies. White arrows indicate lipid bilayer.[8] --- ### Uncharacterized family (Mollivirus genus) - Group 1: dsDNA - 1 species of this virus genus has been identified. (Mollivirus sibericum) - It was first detected in the permafrost of Siberia. - Capsid size is 500-600nm while it has 2 layers of different thickness. - Its genome is linear dsDNA containing 6.51,000 base pairs. - A wide variety of gene structures indicate horizontal gene exchange with the host. - It enters the cell through phagocytosis.[2] ![6](https://i.imgur.com/yWkqeEX.jpg) M. Legendre, Mollivirus sibericum particle at a late assembly stage.[9] --- ### Uncharacterized family (Faustovirus genus) - Group 1: dsDNA - There are 9 species of this virus genus. - Genome size is around 467,592 base pairs. - There are genetic similarities with the African swine fever virus of the Asfarviridae family. - Although Vermamoeba vermiformis, which is generally an amoeba, infects species, it is predicted that they can also colonize mice and cattle. - It enters the cell through phagocytosis.[2] ![7](https://i.imgur.com/qhvKIKf.gif) Trisymmetrons and pentasymmetrons in faustovirus. (A) High defocus micrograph of mature faustovirus particles. A pentasymmetron from a destroyed virus particle that is visible in the background is marked with an arrow. (B) Schematic representation of the arrangement of trisymmetrons and pentasymmetrons in faustovirus. The pentasymmetron at one fivefold axis is shown in green, and the central pentamer is highlighted in purple. The trisymmetrons surrounding the pentasymmetron are shown in cyan, and one trisymmetron is highlighted. (Scale bars, 50 nm.)[10] --- {%youtube GxCo5PcVAOc%} This video describes giant viruses and virophages discovered with giant viruses. ---- ### References [1]N. Brandes and M. Linial, "Giant Viruses—Big Surprises", Viruses, vol. 11, no. 5, p. 404, 2019. Available: 10.3390/v11050404. [2]B. Tokarz-Deptuła, P. Niedźwiedzka-Rystwej, P. Czupryńska and W. Deptuła, "Protozoal giant viruses: agents potentially infectious to humans and animals", Virus Genes, vol. 55, no. 5, pp. 574-591, 2019. Available: 10.1007/s11262-019-01684-w. [3]J. Van Etten et al., "Phycodnaviruses (Phycodnaviridae)", 2021. Image Reference: [4]N. Zauberman et al., "Distinct DNA Exit and Packaging Portals in the Virus Acanthamoeba polyphaga mimivirus", PLoS Biology, vol. 6, no. 5, p. e114, 2008. Available: 10.1371/journal.pbio.0060114. [5]"Return of the giant zombie virus", Science News for Students,2014. [Online]. Available: https://www.sciencenewsforstudents.org/article/return-giant-zombie-virus. [Accessed: 02- Jun- 2021]. [6]2013. [Online]. Available: http://www.sci-news.com/biology/science-pandoravirus-giant-01253.html. [Accessed: 02- Jun- 2021]. [7]"Phycodnaviridae - Alchetron, The Free Social Encyclopedia", Alchetron.com, 2018. [Online]. Available: https://alchetron.com/Phycodnaviridae. [Accessed: 02- Jun- 2021]. [8]"Marseilleviridae | Wikiwand", Wikiwand. [Online]. Available: https://www.wikiwand.com/en/Marseilleviridae. [Accessed: 02- Jun- 2021]. [9]2015. [Online]. Available: http://www.sci-news.com/biology/science-mollivirus-sibericum-giant-virus-03221.html. [Accessed: 02- Jun- 2021]. [10]T. Klose et al., "Structure of faustovirus, a large dsDNA virus", Proceedings of the National Academy of Sciences, vol. 113, no. 22, pp. 6206-6211, 2016. Available: 10.1073/pnas.1523999113 [Accessed 2 June 2021].