Labyrinthula
| Labyrinthula | |
|---|---|
| Scientific classification | |
| Domain: | Eukaryota |
| (unranked): | SAR |
| (unranked): | Heterokonta |
| Phylum: | Bigyra |
| Subphylum: | Sagenista |
| Class: | Labyrinthulae |
| Order: | Labyrinthulida |
| Family: | Labyrinthulidae |
| Genus: | Labyrinthula |
The genera Labyrinthula is part of the group Labyrinthulomycetes and contains thirteen species. The major feature of this genera is the formation of an endoplasmic net secreted by specialized organelles called bothrosomes which surrounds the colony, which is also used by Labyrinthula for moving. The protist reproduces by zoosporulation as it sets some flagellated spores free from a sporangium. Zoospores prove the belonging of Labyrinthula in the Heterokont phylum due to the distinct flagellar morphology, in which the anterior one is covered in mastigonemes.
The interest in Labyrinthula arose as it has been identified as the cause of the "wasting disease", which led to the death of more than 90\% of the seagrass population of the North Atlantic coast in the early 1930s.
A labyrinth is a synonym of a maze, reflecting the ectoplasmic net, which gives the protist a net-like shape which resembles a maze.
Cienkowski was the first person who published on Labyrinthula in 1867. He studied primarily the morphology, and he identified two species: Labyrinthula vitelli and Labyrinthula macrocystis.
In 1967, Pokorny published the first review over Labyrinthula and counted ten marine species, two freshwater species and one terrestrial species.
Before being considered as protists and Stramenopiles, Labyrinthula had been classified in the Mycetozoa, the slime molds and the Rhizopodia.
Interest in Labyrinthula started when it was defined as the cause of the "wasting disease". An epidemic happened in the 1930s in the North American and European coasts, killing over 90% of the seagrass (Zostera marina) population. The first description of similar symptoms in terrestrial grasses happened in 1995 in California. The target organism is turfgrass and the pathogen identified by the Koch's postulates is L. terrestris. Both seagrass and turfgrass can be infected by organisms of the Labyrinthula genera, but from different species, one marine and one terrestrial one, respectively.
The habitat of Labyrinthula is very diverse, they are found in marine and freshwater environments as well as in terrestrial environments all over the world. Labyrinthula have been found to live as pathogens, commensals or mutualists on several host organisms. One example is the endosymbiont Labyrinthula sp. inside Thecamoeba hilla, which seem to live as mutualists symbionts.
The morphology of a single cell of Labyrinthula is not unique and varies a lot between the different species. The cells can be spindle-shaped like L. macrocystis, spherical or ovoid to name only a few examples. The spindle shape is due to the microtubules of the cytoskeleton. There is no mean size of one cell, because of the diversity between the species. An approximation can still be made at 8-30 γm in length and 1.5-8 γm in width. The general morphology of the cell contain one central nucleus, the smooth endoplasmatic reticulum, mitochondria with tubular cristae, numerous lipid-composed granules and two large Golgi complexes. Labyrinthula are non-photosynthetic and are usually translucent white, but some yellow strains have been observed.
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