Labyrinthulomycetes
{{short description|Class of protists that produce a filamentous network}}
{{Automatic taxobox
| image = Aplanonet3.jpg
| image_caption = Cell with network of ectoplasmic filaments (Aplanochytrium sp.)
| image_alt =
| taxon = Labyrinthulomycetes
| authority = Arx, 1970, Dick, 2001
| subdivision =
| synonyms =
- Labyrinthulomycota Whittaker, 1969
- Labyrinthomorpha Page in Levine et al., 1980
- Labyrinthulea Olive, 1975
ex Cavalier-Smith, 1989
}}
Labyrinthulomycetes (ICNafp) or Labyrinthulea (ICZN) is a class of protists that produce a network of filaments or tubes, 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.
Characteristics
{{unreferenced section|date=August 2023}}
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
= Evolutionary origin =
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.
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.
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.
{{clade|style=font-size:90%;|label1=Stramenopiles|1={{clade|2=Platysulcea|1={{clade|sublabel2=plastid loss|label2=Bigyra|2={{clade|label1=Opalozoa|1={{clade|1=Placidozoa 50px|2=Bicosoecida 50px}}|label2=Sagenista|2={{clade|1=Labyrinthulomycetes 50px|2=Eogyrea}}}}|label1=Gyrista|1={{clade|1=Ochrophyta 50px|sublabel2=plastid loss|2=Pseudofungi 50px}}}}}}}}
Classification
Labyrinthulomycetes or Labyrinthulea used to compose the defunct fungal phylum Labyrinthulomycota. 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.
- Order Labyrinthulales/Labyrinthulida {{au|E. A. Bessey 1950/Doffein 1901}}
- Family Aplanochytriaceae/Aplanochytriidae {{au|Leander ex Cavalier-Smith 2012}}
- Aplanochytrium {{au|Bahnweg & Sparrow 1972}} [=Labyrinthuloides {{au|Perkins 1973}}]
- Family Labyrinthulaceae/Labyrinthulidae {{au|Haeckel 1868/Cinekowksa 1867}}
- Labyrinthomyxa {{au|Duboscq 1921}}
- Pseudoplasmodium {{au|Molisch 1925}}
- Labyrinthula {{au|Cienkowski 1864}} [=Labyrinthodictyon {{au|Valkanov 1969}}; Labyrinthorhiza {{au|Chadefaud 1956}}]
- Family-level clade "Stellarchytriaceae/Stellarchytriidae" – this group is provisionally placed in Labyrinthulida but, according to phylogenetic analyses, diverges before the rest of labyrinthulean clades.
- Stellarchytrium {{au|FioRito & Leander 2016}}
- Order Oblongichytriales/Oblongichytrida
- Family Oblongichytriaceae/Oblongichytriidae {{au|Cavalier-Smith 2012}}
- Oblongichytrium {{au|Yokoyama & Honda 2007}}
- Order Thraustochytriales/Thraustochytrida {{au|Sparrow 1973}}
- Pyrrhosorus Juel 1901
- Thanatostrea Franc & Arvy 1969
- Family Althornidiaceae/Althorniidae {{au|Jones & Alderman 1972}}
- Althornia {{au|Jones & Alderman 1972}}
- Family Thraustochytriacae/Thraustochytriidae {{au|Sparrow ex Cejp 1959}}
- Japanochytrium Kobayasi & Ôkubo 1953
- Monorhizochytrium Doi & Honda 2017
- Sicyoidochytrium Yokoy., Salleh & Honda 2007
- Aurantiochytrium Yokoy. & Honda 2007
- Ulkenia Gaertn. 1977
- Parietichytrium Yokoy., Salleh & Honda 2007
- Botryochytrium Yokoy., Salleh & Honda 2007
- Schizochytrium Goldst. & Belsky emend. Booth & Mill.
- Thraustochytrium Sparrow 1936
- Hondaea Amato & Cagnac 2018
- Labyrinthulochytrium Hassett & Gradinger 2018''
- Order "Amphitremidales"/Amphitremida {{au|Gomaa et al. 2013}}
- Family "Amphitremidiaceae"/Amphitremidae {{au|Poch 1913}}
- Paramphitrema {{au|Valkanov 1970}}
- Archerella {{au|Loeblich & Tappan 1961}}
- Amphitrema {{au|Archer 1867}}
- Family "Diplophrydaceae"/Diplophryidae {{au|Cavalier-Smith 2012}}
- Diplophrys {{au|Barker 1868}}
- Order "Amphifilales"/Amphifilida {{au|Cavalier Smith 2012}}
- Family Sorodiplophryidae Cavalier-Smith 2012
- Sorodiplophrys Olive & Dykstra 1975
- Fibrophrys Takahashi et al. 2016
- Family Amphifilidae Cavalier-Smith 2012
- Genus Amphifila Cavalier-Smith 2012
Genetic code
The labyrinthulomycete Thraustochytrium aureum is notable for the alternative genetic code of its mitochondria which use {{mono|TTA}} as a stop codon instead of coding for Leucine. This code is represented by NCBI translation table 23, Thraustochytrium mitochondrial code.
| class="wikitable" style="border: none; text-align: center;"
|+ | ||||||
| style="width: 250px;" | Genetic code | style="width: 25px;" | Translation table | style="width: 50px;" | DNA codon | style="width: 50px;" | RNA codon | colspan="3" style="width: 150px;" | Translation with this code | style="border: none; width: 1px;" | | style="width: 150px;" | Standard code (Translation table 1) |
|---|---|---|---|---|---|---|
| rowspan="1" | Thraustochytrium mitochondrial | rowspan="1" | 23 | {{mono|TTA}} | {{mono|UUA}} | colspan="3" style="background-color:#B0B0B0;" | {{mono|STOP {{=}} Ter}} {{mono|(*)}} | style="border: none; width: 1px;" | | style="background-color:#ffe75f;" | {{mono|Leu}} {{mono|(L)}} |
Gallery
File:Aplanolm.jpg|Aplanochytrium sp. under light microscope
File:Aplanosem.png|Aplanochytrium sp. under SEM
File:Aurantiochytrium limacinum SR21.jpg|Aurantiochytrium sp.
File:Collection Penard MHNG Specimen 48-2-4 Amphitrema stenostoma.tif|Test of Amphitrema, a testate amoeba recently included in the group
File:Tsenkovsky Lev Semyonovich.jpg|Leon Cienkowski, Russian botanist who in 1867 described Labyrinthula, the first genus of the groupCienkowski, L. (1867). Ueber den Bau und die Entwicklung der Labyrinthuleen. Arch. mikr. Anat., 3:274, [https://www.biodiversitylibrary.org/item/110292#page/288/mode/1up].
References
{{Reflist|refs=
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External links
{{EB1911 Poster|Labyrinthulidea}}
- [https://web.archive.org/web/20070417091256/http://www.botany.uga.edu/zoosporicfungi/labyrint.htm Labyrinthulomycota]
{{wikispecies}}
{{Heterokont}}
{{Taxonbar|from1=Q1148791|from2=Q16653009|from3=Q131275915}}