Choanovirus
| "Choanovirus" | ||||||||||||||||||
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| Scientific name | ||||||||||||||||||
| "Choanovirus" | ||||||||||||||||||
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| ChoanoV |
" Choanovirus " refers to a genus of giant viruses from the phylum Nucleocytoviricota (formerly Nucleocytoplasmic large DNA viruses , NCLDV ) with double-stranded DNA - genome (dsDNA) as in September 2019 from David M. Needhal, Alexandra Z. Worden (from GEOMAR Helmholtz - Center for Ocean Research in Kiel ) and colleagues based on metagenomic analyzes of samples from the Northeast Pacific . Giant viruses are nucleocytoplasmic large DNA viruses with more than approx. 300 kilobase pairs . According to the analyzes, the choanoviruses parasitize marine unicellular organisms from the group of collar flagellates ( choanoflagellates - hence the name). These are widespread unicellular predators ( protists ) and are close to multicellular animals ( metazoa ). Although only known from a metagenomic analysis , there are clear indications that " Choanovirus 1 " (ChoanoV1) actually parasitized the choanoflagellates as its hosts , and was not accidentally snatched up with prey or directly ingested by them as prey. Among the choanoflagellates, the first authors probably suspect the species Bicosta minor ( Acanthoecidae , Choanoflagellida ) as the host species .
The results suggest that light-dependent energy transfer systems could often be components of giant viruses in both photoautotrophic (photosynthetic) and phagotrophic (predatory) unicellular marine eukaryotes .
Genome
ChoanoV1
A virus genome of 875 kbp was initially compiled by the first authors using metagenome sequencing ( Choanovirus 1 , ChoanoV1). This represented the largest marine virus genome ever sequenced. The GC content was determined to be a low 21%, only comparable with the non-marine hokovirus (HokV: 21.4%) and cafeteria roenbergensis virus (CroV: 23%).
According to the analyzes, the genome of ChoanoV1 encodes an estimated 862 proteins , a new record for pelagic (marine) ecosystems to date . No homologues in other species could currently be found for almost 442 of these proteins .
In addition, there are three proteins from the class of type 1 rhodopsin (visual pigment rhodopsin , channelrhodopsin ), which is why they are called VirR (viral rhodopsin). When exposed to light, these rhodopsins pump protons ( hydrogen cations ) and thus, like cellular rhodopsins, generate a proton-moving force (potential). One of them, VirR DTS , resembles another putative virus rhodopsin found in the giant virus " Phaeocystis globosa virus 16 " (PgV-16T). The viruses labeled PgV all parasitize the marine alga Phaeocystis globosa ( Haptophyta ). Unlike the algae virus PgV-16T, choanoviruses encode the entire biosynthetic pathway of the pigment. Both virus rhodopsins are more similar in crystal structure to each other than to any known rhodopsin of cellular organisms. The VirR proteins of the choanoviruses do not appear to be derived from today's opistho accounts. Rather, they could have already acquired ancestors of today's viruses before they expanded their host spectrum to include various algae and heterotrophs (such as the choanoflagellates).
ChoanoV2
Another sample from the Northeast Pacific, taken seven years earlier, was examined by the first authors, as this also indicated a low GC content and rRNA of B. minor . The result brought a genetic match of 89% with ChoanoV1 (with even 94% match of the coded amino acids ) and was therefore designated as "Choanovirus 2" (ChoanoV2). Unfortunately, the genome of this sample was more fragmented than that of the first (ChoanoV1).
Proteome
Most of the choanovirus proteins in agreement with eukaryotic proteins were opisthocaccount -like, suggesting that the coding genes were previously acquired by the hosts ( host-to-virus horizontal gene transfer , H2V HGT).
Chitinase
One of the proteins with known counterparts (in addition to rhodopsins) belongs to the group of chitinases ( chitin- degrading enzymes). The polysaccharide chitin is the main component of the exoskeleton of insects and crustaceans (collectively Pancrustacea ); it occurs in zooplankton , some algae and many other organisms and is therefore often found in oceans. Chitinases break down this structural substance into saccharides , which can then be easily absorbed and processed by marine microbes , for example.
Viral chitinases were previously only known from insect viruses (in particular from butterflies including moths, for example the Autographa californica nucleopolyhedrovirus , Baculoviridae ) and from viruses of the freshwater alga Chlorella ( Chlorovirus species, Phycodnaviridae ). The results support the assumption that the chitinases of the three virus groups (the insect viruses, chlorella viruses and choanoviruses) were acquired by the respective hosts in independent events.
There are currently (autumn 2019) two ways in which the chitinases could use the choanoviruses:
- It could help the hosts, potentially weakened by the virus, to digest (metabolize) their food (prey) better, for the common benefit of the host and virus.
- there is a still unknown chitin-containing cell structure in the choanoflagellates ( e.g. Theca ), which the virus would break down in the course of a lysis for its sole benefit.
In any case, the chitinases should ensure that, after the virus-induced lysis of the unicellular organism, its remains (in the form of easily usable monosaccharides) are available to the marine biological cycle more quickly, with corresponding effects on the entire marine ecosystem .
tRNAs
The choanoviruses also encode 22 tRNAs . The number of encoded tRNA increases roughly with the total size of the genome, the larger Tupan virus from deep-sea sediments codes 48, the smaller pelagic giant viruses - " Tetraselmis virus " (TetV), Cafeteria roenbergensis virus (CroV), " Phaeocystis globosa virus 16 " ( PgV-16T) and “ Chrysochromulina ericina virus ” (alias “ Haptolina ericina virus ”, CeV) - encode 18 to 22 tRNAs. The choanovirus tRNAs correspond to the most commonly used amino acids - apparently exactly those most important for the virus are retained by it.
Systematics
About 20% of the ChoanoV1 proteins and 23% of the more fragmented ChoanoV2 proteins showed agreement with known proteins from representatives of the nucleocytoplasmic large DNA viruses (NCLDV), which suggests that they belong to the Choanoviruses. The NCLDV are a diverse family group of eukaryotic dsDNA viruses that has not yet been confirmed by the International Committee on Taxonomy of Viruses (ICTV) - as of March 2019 - by suggestion of the rank of an order (then also called " Megavirales ") or higher. All known giant viruses (genome with more than 300 bases or base pairs) belong to this group so far (September 2019), as well as the smaller smallpox viruses .
The reconstruction of the phylogenetic relationships further showed that the choanoviruses belong to the extended Mimiviridae and, compared to the established 'classic' Mimiviridae ( mimiviruses , Tupan viruses , toilet new viruses and cafeteria viruses ) represent a branching branch (i.e. a new clade ). Metagenome sequences from the Pacific Ocean , Atlantic Ocean and Southern Ocean indicate a broad marine group of viruses, even if their hosts are generally unknown.
A close comparison of orthologous protein groups of the choanoviruses and the NCLDVs places ChoanoV1 next to the only other sequenced marine pelagic virus, the host of which is also a heterotrophic predator, the Cafeteria roenbergensis virus (CroV, parasitizes Cafeteria roenbergensis ). In detail, according to Needham, Worden and colleagues (2019), the systematics of the Mimiviridae (supplemented by common names in this family) roughly give the following picture:
| " Imitervirales " (extended Mimiviridae ) |
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literature
- Jean-Michel Claverie, Chantal Abergel: Mimiviridae : An Expanding Family of Highly Diverse Large dsDNA Viruses Infecting a Wide Phylogenetic Range of Aquatic Eukaryotes]. In: Viruses . 2018 Sep; 10 (9), September 18, 2018, p. 506, doi: 10.3390 / v10090506 , PMC 6163669 (free full text), PMID 30231528 , Tab. 2
Individual evidence
- ↑ a b c d e ICTV: ICTV Master Species List 2019.v1 , New MSL including all taxa updates since the 2018b release, March 2020 (MSL # 35)
- ↑ a b Jonathan Filée: Giant viruses and their mobile genetic elements: the molecular symbiosis hypothesis , in: Current Opinion in Virology, Volume 33, December 2018, pp. 81-88; bioRxiv : 2018/04/11/299784 ( preprint full text)
- ↑ a b c d e f g h i j k l m n o p q r David M. Needham, Susumu Yoshizawa, Toshiaki Hosaka, Camille Poirier, Chang Jae Choi, Elisabeth Hehenberger, Nicholas AT Irwin, Susanne Wilken, Cheuk-Man Yung, Charles Bachy, Rika Kurihara, Yu Nakajima, Keiichi Kojima, Tomomi Kimura-Someya, Guy Leonard, Rex R. Malmstrom, Daniel R. Mende, Daniel K. Olson, Yuki Sudo, Sebastian Sudek, Thomas A. Richards, Edward F. . DeLong, Patrick J. Keeling, Alyson E. Santoro, Mikako Shirouzu, Wataru Iwasaki, Alexandra Z. Worden: A distinct lineage of giant viruses brings a rhodopsin photosystem to unicellular marine predators , in: PNAS, 23 September 2019, doi: 10.1073 / pnas.1907517116 , ISSN 0027-8424 , PDF , including Supplement 1 (xlsx)
- ↑ a b c d e Jan Osterkamp: Biggest giant virus with mysterious additional features , on: Spektrum.de from 23 September 2019
- ↑ Frederik Schulz, Natalya Yutin, Natalia N. Ivanova, Davi R. Ortega, Tae Kwon Lee, Julia Vierheilig, Holger Daims, Matthias Horn, Michael Wagner: Giant viruses with an expanded complement of translation system components . In: Science . 356, No. 6333, April 7, 2017, ISSN 0036-8075 , pp. 82-85. doi : 10.1126 / science.aal4657 .
- ↑ a b c The virus species proposed as " Phaeocystis globosa virus " (PgV) apparently consists of various, not closely related viruses. While PgV-01T could still remain in the genus Prymnesiovirus , family Phycodnaviridae , PgV-16T seems to belong to the OLPG group, which is now part of the extended Mimiviridae (Claverie et al. , 2018) The authors Needham, Worden et al. (2019) only give the acronym PgV in the main part of the work . In supplement S1, however, they designate the virus PgV-16T precisely with PgV, and in FIG. 2a they locate the phylogenetic virus, which they merely refer to as PgV, among the extended Mimiviridae (now order Imitervirales ). Therefore it is clearly always PgV-16T.
- ↑ Aare Abroi, Julian Gough: Are viruses a source of new protein folds for organisms? - Virosphere structure space and evolution , in: Bioessays, Volume 33, No. 8, June 1, 2011, pp. 626-635, doi: 10.1002 / bies.201000126
- ↑ Carole J. Thomas, Helen L. Brown, Chris R. Hawes, Bum Yong Lee, Mi-Kyung Min, Linda A. King, Robert D. Possee1: Localization of a baculovirus-induced chitinase in the insect cell endoplasmic reticulum , in : J. Virol. 72, 1998, pp. 10207-10212, PMC 110568 (free full text), PMID 9811762
- ↑ Guillaume Blanc, Garry Duncan, Irina Agarkova, Mark Borodovsky, James Gurnon, Alan Kuo, Erika Lindquist, Susan Lucas, Jasmyn Pangilinan, Juergen Polle, Asaf Salamov, Astrid Terry, Takashi Yamada, David D. Dunigan, Igor V. Grigoriev, Jean-Michel Claverie, James L. Van Etten: The Chlorella variabilis NC64A genome reveals adaptation to photosymbiosis, coevolution with viruses, and cryptic sex , in: Plant Cell 22, 2010, pp. 2943-2955, doi: 10.1105 / tpc.110.076406
- ↑ a b c Christopher R. Schvarcz, Grieg F. Steward: A giant virus infecting green algae encodes key fermentation genes , in: Virology, Volume 518, May 2018, pp. 423–433, doi: 10.1016 / j.virol.2018.03 .010
- ↑ a b c d e f Lucie Gallot-Lavallee, Guillaume Blanc, Jean-Michel Claverie: Comparative genomics of Chrysochromulina Ericina Virus (CeV) and other microalgae-infecting large DNA viruses highlight their intricate evolutionary relationship with the established Mimiviridae family , in: J. Virol., April 26, 2017, doi: 10.1128 / JVI.00230-17
- ↑ Koonin EV, Dolja VV, Krupovic M, Varsani A, Wolf YI, Yutin N, Zerbini M, Kuhn JH: Create a megataxonomic framework for DNA viruses encoding vertical jelly roll-type major capsid proteins filling all principal taxonomic ranks . ICTV Proposal 2019.003G, April – July 2019
- ↑ Jônatas Abrahão, Lorena Silva, Ludmila Santos Silva, Jacques Yaacoub Bou Khalil, Rodrigo Rodrigues, Thalita Arantes, Felipe Assis, Paulo Boratto, Miguel Andrade, Erna Geessien Kroon, Bergmann Ribeiro, Ivan Bergier, Herve Seligmann, Eric Ghigo, Philippe Colson, Anthony Levasseur, Guido Kroemer, Didier Raoult, Bernard La Scola: Tailed giant Tupanvirus possesses the most complete translational apparatus of the known virosphere . In: Nature Communications . 9, No. 1, February 27, 2018. doi : 10.1038 / s41467-018-03168-1 .
- ↑ M. Moniruzzaman, ER Gann, SW Wilhelm: Infection by a Giant Virus (AaV) Induces Widespread Physiological Reprogramming in Aureococcus anophagefferens CCMP1984 - A Harmful Bloom Algae , in: Front Microbiol. 9, April 19, 2018, p. 752, doi: 10.3389 / fmicb.2018.0075
- ↑ Mohammad Moniruzzaman, Gary R. LeCleir, Christopher M. Brown, Christopher J. Gobler, Kay D. Bidle, William H. Wilson, Steven W. Wilhelm: Genome of brown tide virus (AaV), the little giant of the Megaviridae, elucidates NCLDV genome expansion and host – virus coevolution , in: Virology, Volume 466–467, October 2014, online July 14, 29134, pp. 60–70, doi: 10.1016 / j.virol.2014.06.031
- ↑ Virginia Tech: Viral Dark Matter: Giant Viruses Have Metabolic Genes - Even Though Viruses Don't Have a Metabolism , on: SciTechDaily from April 6, 2020 (photo)
- ↑ a b 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
- ↑ New giant virus discovered - virus detected off Hawaii is the largest cell parasite of plant organisms to date, on: scinexx from May 4, 2018