Platanovirus
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| "Platanovirus" |
" Platanovirus saccamoebae " is a proposed virus species of giant viruses ( NCLDVs ) with double-stranded DNA (dsDNA) in the family Mimiviridae . Amoeba of the species Saccamoeba lacustris ( Tubulinea : Euamoebida / Tubulinida : Hartmannellidae ) serve as hosts . These were isolated from the bark of a plane tree ( Platanus occidentalis , English plane tree, sycamore tree ), hence the name. The isolate KSL-5 (also written KSL5) that was initially found is the first giant virus reported in amoebas of the Saccamoeba genus . Another isolate, KSL-5x (or KSL5x), has since been found. As of April 2019, the platanoviruses have not yet been confirmed by the International Committee on Taxonomy of Viruses (ICTV).
construction
The virus particles ( virions ) of " Platanovirus saccamoebae " KSL-5 are polyhedral (with a fluidized English vortex ) on one side and a neck or stem-like projection at the opposite end. Like Acanthamoeba polyphaga mimivirus (APMV, wild type M1), they are covered by fibrils (protein filaments). In general , they show many similarities in their ultrastructure to other giant viruses of the Mimiviridae family . The average size of their capsids is 290 nm , the length of the fibrils is about 140 nm, which leads to a mean virion size of 430-450 nm. Their virus capsids are smaller than those of other Mimiviridae (especially of the genus Mimivirus ), but the fibrils are longer.
Genome
The genome of the platanoviruses consists of double-stranded DNA. A preliminary sequence analysis showed that KSL-5 is very similar to “ Megavirus chilensis ” (~ 75%).
Propagation cycle
Replication of KSL-5 started after a long delay of at least 12 hours. After 18 hours, first virus particles and a developing were virus factory ( English virus factory ) was detected, at a maximum after 30 hours. The virus factory was comparable in appearance to the virus factory at Acanthamoeba (examples: infections of A. polyphaga by APMV or A. castellanii by Acanthamoeba castellanii mamavirus , ACMV). Virus factory development began after a much longer lag period (12 to 18 hours) compared to other Mimiviridae (only 4 to 5 hours there) and the virus factory was smaller. The formation (assembly) of the virus particles was observed mainly at the periphery of the virus factory, beginning with the formation and assembly of precursor membranes. However, viable host cells were still present 96 hours after infection.
Hosts
Only two S. lacustris lines could be infected as hosts: SL-5 as well as SL-elo. Virus factories were also created in SL-elo, but at 1–2 μm they were smaller than in the original host SL-5 (3.5–6 μm there). The infection was self-limiting and resolved after a few cycles of transmission.
All attempts to transfer KLS-5 to other amoeba , including several Acanthamoeba species, have failed. The fact that only Saccamoeba lacustris strains are susceptible to the KLS-5 virus indicates a highly specific virus system.
Satellite virus
Satellite viruses were also found when SL-5 was infected with KSL-5 viruses : 24 hours after infection, the first small icosahedral virions with a diameter of 50-60 nm were visible in the virus factory, where they apparently replicated. Small virus capsids were detected in empty capsids of the giant virus, which resulted in defective giant virus particles. If the giant virus was missing, Saccamoeba lacustris SL5-5 showed no signs of infection with the small satellite virus, so the giant virus is a necessary helper virus for them . The co-infection with the small virus led to a reduction in the production of the KSL-5 capsids by 70%. The small satellite virus therefore appears to significantly disrupt the replication of KSL-5 in favor of the host cell. In this respect it behaves like the virophage Sputnik , and not like Zamilon . Assuming that it is actually a new virophage, the name " Comedo Virophage " or " Comedo virus " was proposed for the platanovirus saccamoebae virophage of the KSL-5 virus (from Latin comedere , 'eat', 'devour' ).
No associated satellite viruses could be observed in saccamoeba of the strain SL-elo.
Another isolate
In a further experiment, a virus-free strain of the host amoeba SL-5 was mixed with crushed material from the same plane tree, which led to the isolation of a second giant virus KLS-5x (alias KSL5x). This second isolate KSL-5x infects the host cells even more than the first KSL-5. The virus factory is of star shape with long extensions (stem, English Projections ). Within two days, the entire host cell was completely filled with virus particles, which ultimately caused the cells to burst. The virions have very long necks or stems, comparable to those of some bacteriophages (examples: phage T4 , phage lambda ). Opposite the stem is a five-pointed star structure similar to the 'Stargate' of other Mimiviridae . the match in the genome between KSL-5 and KSL-5x is 99%.
In nature, no infection of KSL-5x by the satellite viruses was observed; it was only possible to reproduce isolated satellite viruses in KSL-5x and suitable saccamoeba under laboratory conditions. This also indicates a highly specialized host-virus-virophage system.
Systematics
" Platanovirus saccamoebae " is currently (as of April 2019) not yet officially recognized by the International Committee on Taxonomy of Viruses (ICTV), so all names are still proposed. " Platanovirus " is with the Mimiviridae s. s. (conventional Mimiviridae , without extension by representatives previously assigned to the Phycodnaviridae ) more closely related than with other giant viruses, so belongs in particular to the Phylum Nucleocytoviricota (formerly Nucleocytoplasmic large DNA viruses , NCLDV ). Among these, there is the greatest relationship to the recently discovered, also not yet ICTB-confirmed " Tupan virus " (from an alternative point of view also " Megavirus chiliensis "). Together with “ Tupan virus ” and the other “ satyr virus ” proposed after metagenomic analyzes of soil samples , “ Platanovirus ” is not assigned to any of the conventional Mimivirus lines ( clades ) A, B or C, but one of them together with a separate line.
Individual evidence
- ↑ a b c d e ICTV: ICTV Taxonomy history: Acanthamoeba polyphaga mimivirus , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
- ↑ Christoph M. Deeg, Cheryl-Emiliane T. Chow, Curtis A. Suttle: The kinetoplastid-infecting Bodo saltans virus (BsV), a window into the most abundant giant viruses in the sea ... , in: eLife Sciences 7, March 2018 , doi: 10.7554 / eLife.33014
- ↑ Center national de la recherche scientifique: List of the main “giant” viruses known as of today (March 2019) , Université Aix Marseille, March 2019.
- ↑ a b c Frederik Schulz, Lauren Alteio, Danielle Goudeau, Elizabeth M. Ryan, Feiqiao B. Yu, Rex R. Malmstrom, Jeffrey Blanchard, Tanja Woyke: Hidden diversity of soil giant viruses . In: Nature Communications , volume 9, November 19, 2018, Article number: 4881, doi: 10.1038 / s41467-018-07335-2
- ↑ Platanovirus is not to be confused with the species Banana bunchy top virus , Spanish Plátano virus bunchy top , in the genus Babuvirus of the family Nanoviridae .
- ↑ a b c d e Bärbel Hauröder, Liane Junglas, Silke Loch, Rolf Michel, Karl-Dieter Müller, Claudia Wylezich: Experimental co-infection of Saccamoeba lacustris with Mimivirus-like Giant virus and a small Satellite virus , in: Open Agrar, 15th May 2018
- ↑ a b c d e f g h i j k Bärbel Hauröder, Claudia Wylezich, Liane Junglas, Silke Loch, Jenny Eisenkolb, Rolf Michel: New Giant Virus in Free-Living Amoeba , in: Imaging & Microscopy from July 20, 2018, Central Hospital of the Deutsche Bundeswehr Medical Services, Koblenz
- ↑ Other infested giant viruses amoebae genera are Vermamoeba ( Kaumoebavirus , Faustovirus , Orpheovirus ) and Acanthamoeba ( Mimivirus with Acanthamoeba polyphaga Mimivirus and " Mama Virus ", " Moumouvirus " with Amov, " Pacman Virus ", " Medusa Virus ", " Pithovirus ", " Molli virus ," " Cedratvirus "), while in others such as Entamoeba as well as Thecamoeba and Stenamoeba no such parasites are apparently known.
- ↑ ICTV: ICTV Master Species List 2018b.v2 MSL # 34v
- ↑ a b c d e Said Mougari, Dehia Sahmi-Bounsiar, Anthony Levasseur, Philippe Colson, Bernard La Scola: Virophages of Giant Viruses: An Update at Eleven , in: Viruses 11 (8), July / August 2019, 733, doi : 10.3390 / v11080733
- ↑ Claudia Wylezich, Bärbel Hauröder, Dirk Höper, Martin Beer: A new giant virus isolated from its natural host Saccamoeba sp. together with its virophage shows a narrow host range , in: Conference: 38th meeting of the german Society for Protozoology (DGP), At Vienna / Austria, February 2019
- ↑ Said Mougari, Dehia Sahmi-Bounsiar, Anthony Levasseur, Philippe Colson, Bernard La Scola: Virophages of Giant Viruses: An Update at Eleven , in: Viruses 11 (8), August 8, 2019, p. 733, doi: 10.3390 / v11080733 , PMC 6723459 (free full text), PMID 31398856 , section 3.1.5
- ↑ List of the main “giant” viruses known as of today (PDF) Université Aix Marseille, Center national de la recherche scientifique, April 18, 2018.