Labyrinthulomycetes (ICNafp) or Labyrinthulea
Characteristics
Although they are outside the cells, the filaments of Labyrinthulomycetes are surrounded by a
cell membrane. They are formed and connected with the cytoplasm by a unique organelle called a sagenogen or bothrosome. The cells are
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
within the
Stramenopiles. They belong to the phylum
Bigyra, which contains other heterotrophic microorganisms such as the
. 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
secondary loss 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 . The zoospores of 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.
Classification
Labyrinthulomycetes or Labyrinthulea used to compose the defunct fungal
phylum Labyrinthulomycota.
They were originally considered unusual
, 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
, 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.
Genetic code
The labyrinthulomycete
Thraustochytrium aureum is notable for the alternative genetic code of its
mitochondria which use as a
stop codon instead of coding for
Leucine.
This code is represented by NCBI translation table 23,
Thraustochytrium mitochondrial code.
== Gallery ==
, Russian botanist who in 1867 described
Labyrinthula, the first genus of the group
[Cienkowski, L. (1867). Ueber den Bau und die Entwicklung der Labyrinthuleen. Arch. mikr. Anat., 3:274, [1].]]]
External links
