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Labyrinthulomycetes

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Labyrinthulomycetes (ICBN) or Labyrinthulea[2] (ICZN) is a class of protists that produce a network of filaments or tubes,[3] which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the labyrinthulids (or slime nets) and thraustochytrids. They are mostly marine, commonly found as parasites on algae and seagrasses or as decomposers on dead plant material. They also include some parasites of marine invertebrates and mixotrophic species that live in a symbiotic relationship with zoochlorella.[4][5][6]

Labyrinthulomycetes
Cell with network of ectoplasmic filaments (Aplanochytrium sp.)
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Bigyra
Subphylum: Sagenista
Class: Labyrinthulomycetes
Arx, 1970, Dick, 2001
Orders[1]
Synonyms
  • Labyrinthulomycota Whittaker, 1969
  • Labyrinthomorpha Page in Levine et al., 1980
  • Labyrinthulea Olive, 1975
    ex Cavalier-Smith, 1989

Characteristics

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Although they are outside the cells, the filaments of Labyrinthulomycetes are surrounded by a membrane. They are formed and connected with the cytoplasm by a unique organelle called a sagenogen or bothrosome. The cells are uninucleated and typically ovoid, and move back and forth along the amorphous network at speeds varying from 5-150 μm per minute. Among the labyrinthulids, the cells are enclosed within the tubes, and among the thraustochytrids, they are attached to their sides.

Evolution

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Evolutionary origin

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Labyrinthulomycetes are not fungi, but a monophyletic group of eukaryotes within the Stramenopiles. They belong to the phylum Bigyra, which contains other heterotrophic microorganisms such as the bicosoecids. Considering that the plastids from Stramenopiles are possibly the result of an event of endosymbiosis in their last common ancestor, the bicosoecids and the labyrinthulomycetes could have originated from a mixotrophic algal common ancestor that secondarily lost their plastids.[3]

Some characteristics of the labyrinthulomycetes can be explained by their origin from ancestral plastids. They produce omega-3 poly-unsaturated fatty acids using a desaturase usually present in chloroplasts. The zoospores of labyrinthulids have an eyespot composed of membrane-bound granules that resembles eyespots of photosynthetic stramenopiles, which are either within a plastid or believed to be derived from a plastid.[3]

Within Bigyra, the labyrinthulomycetes are the sister group to Eogyrea, a class containing the species Pseudophyllomitus vesiculosus and the environmental clade called MAST-4. Together they compose the subphylum Sagenista.[7][8]

Stramenopiles

Classification

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Labyrinthulomycetes or Labyrinthulea used to compose the defunct fungal phylum Labyrinthulomycota.[9] They were originally considered unusual slime moulds, although they are not very similar to the other sorts. The structure of their zoospores and genetic studies show them to be a primitive group of heterokonts, but their classification and treatment remains somewhat unsettled.

This class usually contained two orders, Labyrinthulales and Thraustochytriales (ICBN), or Labyrinthulida and Thraustochytrida (ICZN), but a different classification has recently been proposed.[6][10][11][1][9]

Genetic code

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The labyrinthulomycete Thraustochytrium aureum is notable for the alternative genetic code of its mitochondria which use TTA as a stop codon instead of coding for Leucine.[13] This code is represented by NCBI translation table 23, Thraustochytrium mitochondrial code.[14]

Genetic code Translation
table		 DNA codon RNA codon Translation
with this code		 Standard code
(Translation table 1)
Thraustochytrium mitochondrial 23 TTA UUA STOP = Ter (*) Leu (L)
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References

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  1. ^ a b c Adl SM, Bass D, Lane CE, Lukeš J, Schoch CL, Smirnov A, Agatha S, Berney C, Brown MW, Burki F, Cárdenas P, Čepička I, Chistyakova L, del Campo J, Dunthorn M, Edvardsen B, Eglit Y, Guillou L, Hampl V, Heiss AA, Hoppenrath M, James TY, Karnkowska A, Karpov S, Kim E, Kolisko M, Kudryavtsev A, Lahr DJG, Lara E, Le Gall L, Lynn DH, Mann DG, Massana R, Mitchell EAD, Morrow C, Park JS, Pawlowski JW, Powell MJ, Richter DJ, Rueckert S, Shadwick L, Shimano S, Spiegel FW, Torruella G, Youssef N, Zlatogursky V, Zhang Q (2019). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/jeu.12691. PMC 6492006. PMID 30257078.
  2. ^ Cavalier-Smith, T. (1997). "Sagenista and bigyra, two phyla of heterotrophic heterokont chromists". Archiv für Protistenkunde. 148 (3): 253–267. doi:10.1016/S0003-9365(97)80006-1.
  3. ^ a b c Tsui, Clement K M; Marshall, Wyth; Yokoyama, Rinka; Honda, Daiske; Lippmeier, J Casey; Craven, Kelly D; Peterson, Paul D; Berbee, Mary L (January 2009). "Labyrinthulomycetes phylogeny and its implications for the evolutionary loss of chloroplasts and gain of ectoplasmic gliding". Molecular Phylogenetics and Evolution. 50 (1): 129–40. doi:10.1016/j.ympev.2008.09.027. PMID 18977305.
  4. ^ Schärer, L.; Knoflach, D.; Vizoso, D. B.; Rieger, G.; Peintner, U. (2007). "Thraustochytrids as novel parasitic protists of marine free-living flatworms: Thraustochytrium caudivorum sp. nov. Parasitizes Macrostomum lignano" (PDF). Marine Biology. 152 (5): 1095. doi:10.1007/s00227-007-0755-4. S2CID 4836350.
  5. ^ Pan, Jingwen (2016). Labyrinthulomycetes diversity meta-analysis (MSc). University of British Columbia. doi:10.14288/1.0223199.
  6. ^ a b Gomaa, Fatma; Mitchell, Edward A. D.; Lara, Enrique (2013). "Amphitremida (poche, 1913) is a new major, ubiquitous labyrinthulomycete clade". PLoS One. 8 (1): e53046. Bibcode:2013PLoSO...853046G. doi:10.1371/journal.pone.0053046. PMC 3544814. PMID 23341921.
  7. ^ Cavalier-Smith, Thomas (2017). "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences". Protoplasma. 255 (1): 297–357. doi:10.1007/s00709-017-1147-3. PMC 5756292. PMID 28875267.
  8. ^ Thakur, Rabindra; Shiratori, Takashi; Ishida, Ken-ichiro (2019). "Taxon-rich Multigene Phylogenetic Analyses Resolve the Phylogenetic Relationship Among Deep-branching Stramenopiles". Protist. 170 (5): 125682. doi:10.1016/j.protis.2019.125682. ISSN 1434-4610. PMID 31568885. S2CID 202865459.
  9. ^ a b c Bennett, Reuel M.; Honda, D.; Beakes, Gordon W.; Thines, Marco (2017). "Chapter 14. Labyrinthulomycota". In Archibald, John M.; Simpson, Alastair G.B.; Slamovits, Claudio H. (eds.). Handbook of the Protists. Springer. pp. 507–542. doi:10.1007/978-3-319-28149-0_25. ISBN 978-3-319-28147-6.
  10. ^ Anderson, O. Roger; Cavalier-Smith, Thomas (2012). "Ultrastructure of Diplophrys parva, a New Small Freshwater Species, and a Revised Analysis of Labyrinthulea (Heterokonta)". Acta Protozoologica. 8 (1): 291–304. doi:10.4467/16890027AP.12.023.0783.
  11. ^ a b FioRito, Rebecca; Leander, Celeste; Leander, Brian (2016). "Characterization of three novel species of Labyrinthulomycota isolated from ochre sea stars (Pisaster ochraceus)". Marine Biology. 163 (8): 170. doi:10.1007/s00227-016-2944-5. S2CID 43399688.
  12. ^ Hassett, Brandon T.; Gradinger, Rolf (2018). "New Species of Saprobic Labyrinthulea (=Labyrinthulomycota) and the Erection of a gen. nov. to Resolve Molecular Polyphyly within the Aplanochytrids". Journal of Eukaryotic Microbiology. 65 (4): 475–483. doi:10.1111/jeu.12494. hdl:10037/13570. ISSN 1550-7408. PMID 29265676. S2CID 46820836.
  13. ^ Wideman, Jeremy G.; Monier, Adam; Rodríguez-Martínez, Raquel; Leonard, Guy; Cook, Emily; Poirier, Camille; Maguire, Finlay; Milner, David S.; Irwin, Nicholas A. T.; Moore, Karen; Santoro, Alyson E. (2019-11-25). "Unexpected mitochondrial genome diversity revealed by targeted single-cell genomics of heterotrophic flagellated protists". Nature Microbiology. 5 (1): 154–165. doi:10.1038/s41564-019-0605-4. hdl:10871/39819. ISSN 2058-5276. PMID 31768028. S2CID 208279678.
  14. ^ Elzanowski A, Ostell J, Leipe D, Soussov V. "The Genetic Codes". Taxonomy browser. National Center for Biotechnology Information (NCBI), U.S. National Library of Medicine. Retrieved 11 August 2016.
  15. ^ Cienkowski, L. (1867). Ueber den Bau und die Entwicklung der Labyrinthuleen. Arch. mikr. Anat., 3:274, [1].
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Wikisource has the text of the 1911 Encyclopædia Britannica article "Labyrinthulidea".
 
Wikispecies has information related to Labyrinthulomycetes.
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