Chromera velia. Credit: Gert Hanson
Most corals from shallow tropical reefs rely heavily upon an intracellular alga, Symbiodinium, to meet their nutritional demands. This hugely important symbiosis is the foundation on which a coral reef’s biodiversity is built, but, as it turns out, this is not the only algal symbiosis to be found. Over the last twenty years, researchers have been slowly piecing together clues to a startling discovery—a mysterious protozoan with close ties to some of mankind’s worst parasites. To appreciate the importance of this find, we first need to take a stroll through the evolutionary history of these organisms. Symbiodinium is a photosynthetic genus of dinoflagellate, a phylum of protozoa which is defined morphologically by the presence of two flagella and (usually) an armor-like covering called a theca. The group is familiar to aquarists for their occasional tendency to form stubborn blooms on aquarium substrates—similar blooms in coastal habitats can cause the toxic phenomenon known as a “red tide”.
Symbiodinium. Credit: Todd DeJeunesse/Penn State University
Researchers working with Symbiodinium often must physically separate them from their coral host. This requires the maceration and centrifugation of coral tissue to isolate the individual algal cells, followed by growing the algae in a new medium. The technique had been performed for decades, when, in 2001, a couple unusual contaminants were recorded for the first time in Australian samples of Plesiastrea and Leptastrea.These contaminants would eventually be described as new species—Chromera velia and Vitrella brassicaformis. Their discovery was doubly important, as not only had a new coral symbiont been found, but morphological and genetic study indicated that these algae represented an entirely novel phylum of single-celled organism allied closely to the Phylum Apicomplexa—a diverse and exclusively parasitic group that includes the causative agents of malaria, toxoplasmosis, cryptosporidiosis and many other unpleasant and economically important diseases that afflict our species (and our livestock).The apicomplexans are named for a unique type of cellular organelle called an apicoplast, which is situated at the apical end of the organism and used for various metabolic functions and to aid in entering their host’s cells. Because of its uniqueness, the apicoplast is a major focus for research into targeted malarial drugs, but culturing parasitic apicomplexans to allow for such study is no easy feat, as it requires both the host (e.g. human blood) and the vector (e.g.… More:
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