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Summary
In recent decades, nutrient over-enrichment (eutrophication) and climate-change effects have led to a rise in toxin-producing cyanobacterial harmful algal blooms (CyanoHABs) in freshwater systems worldwide (1). Microcystin, the most ubiquitous cyanotoxin, is a serious drinking water threat due to its potent liver toxicity and carcinogenic potential (2). The distribution of microcystin synthetase (mcy) genes across many genera suggests that production of this metabolite was a widely shared trait early in cyanobacterial evolution (3). However, not all cyanobacterial strains have retained this pathway. There is growing evidence that oxidative stressors in high-irradiance surface waters, where blooms accumulate, select for toxigenic strains over their nontoxic counterparts.
