Wilson Tarpey, “Comparing Toxicity of Buoyant and Non-Buoyant Microcystis Populations”
Mentors: Ryan Newton & Todd Miller, Freshwater Sciences & Public Health
Microcystins are a class of toxic compounds naturally produced from certain species of cyanobacteria, and in particular Microcystis species. These cyanobacteria populations experience an exponential growth phase during the summer months, known as a ‘bloom’. These blooms happen readily in eutrophic systems during the warm summer months when photoactive radiation duration and intensity peaks. The environmental drivers of microcystin production are still unknown. Microcystis regulates its position in the water column with a air-filled vacuoles, giving it a unique environmental advantage. Here, we examined how the buoyant state of Microcystis cells affects toxin production in an urban freshwater lagoon along the Lake Michigan coast in Milwaukee, WI, that is persistently affected by toxic Microcystis blooms. From a homogenous mixture, we allowed buoyant Microcystis cells to separate from the rest of the population, and then took a surface sample before re-homogenizing for a second mixed sample. The two samples were analyzed for eleven microcystins and a suite of related peptides including nodularin, anabaenopeptins, cyanopeptolins, and micoginin-690 via liquid chromatography tandem mass spectrometry. Algal pigments chlorophyll a and phycocyanin were measured spectrophotometrically alongside 16s cell counts and toxin producing genes via qPCR. We show that toxin dynamics vary over time, space and under some scenarios between buoyant and non-buoyant populations.
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