Thraustochytrids

Thraustochytrids are single-celled saprotrophic eukaryotes (decomposers) that are widely distributed in marine ecosystems, and which secrete enzymes including, but not limited to amylases, proteases, phosphatases.^{[1][2][3][4][5][6]} They are most abundant in regions with high amounts of detritus and decaying plant material.^[1] They play an important ecological role in mangroves, where they aid in nutrient cycling by decomposing decaying matter.^{[7][8][9][10]} Additionally, they contribute significantly to the synthesis of omega-3 polyunsaturated fatty acids (PUFAs): docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), which are essential fatty acids for the growth and reproduction of crustaceans.^[11][12][13] Thraustochytrids are members of the class Labyrinthulea, a group of protists that had previously been incorrectly categorized as fungi due to their similar appearance and lifestyle.^[14] With the advent of DNA sequencing technology, labyrinthulomycetes were appropriately placed with other stramenopiles and subsequently categorized as a group of Labyrinthulomycetes.

There are several characteristics which are unique to Thraustochytrids, including their cell wall made of extracellular non-cellulosic scales, zoospores with characteristic heterokont flagella, and a bothrosome-produced ectoplasmic net, which is used for extracellular digestion.^{[15][16][17][18][19][20][21][22][23]} Thraustochytrids are morphologically variable throughout their life cycle. They have a main vegetative asexual cycle, which can vary depending on the genus.^[24][10] While sexual reproduction has been observed in this group, it remains poorly understood.^[25]

Thraustochytrids are of particular biotechnical interest due to their high concentrations of docosahexaenoic acid (DHA), palmitic acid, carotenoids, and sterols, all of which have beneficial effects to human health.^{[10][17][26][27][28][29][30][31][32]} Thraustochytrids rely on a plethora of resources such as various sources of organic carbon (vitamins and sugars), and inorganic salts throughout their life cycle.^{[33][34][35][36][37][38][39][40][41]} Scientists have devised several potential uses for thraustochytrids stemming around increasing DHA, fatty acids, and squalene concentrations in vivo by either changing the genetic makeup or medium composition/conditioning.^{[42][43][44][45][46][47][48]} There have also been some breakthroughs which have resulted in gene transfers to plant species in order to make isolation of certain oils easier and cost effective.^[49][50] Thraustochytrids are currently cultured for use in fish feed and production of dietary supplements for humans and animals.^[51][52][53] In addition, scientists are currently researching new methodologies to convert waste water into useful products like squalene, which can then be utilized for the production of biofuel.^{[54][55][56][57][58]}