Cyanotoxins are a global problem due to the increasing frequency of cyanobacterial blooms. They are also present in Slovenian waters. Compared to their impact on human and animal health, their impact on other small primary producers such as microalgae is not well studied. During the MSc thesis, we have tried to evaluate the effect of selected cyanotoxins, microcystin (MC), cylindrospermopsin (CYN), saxitoxin (STX) and anatoxin (ATX) on the growth of the microalga Chlamydomonas reinhardtii. After 3-day exposure to different concentrations of toxins (MC 10-10.000 μg/L, CYN 100-900 μg/L, STX 100-1025 μg/L, ATX 100-400 μg/L), growth inhibition was determined based on the colour of the cultures, the differences in growth rate, and the percentage of inhibition. In addition, changes in cell morphology were observed by microscopy and the effect on chlorophyll autofluorescence intensity was examined. The effects of cyanotoxins were compared with the effects of the positive control, atrazine. MC inhibited the growth of C. reinhardtii at the highest concentration used, while CYN, STX and ATX showed no growth inhibition at any concentrations tested. Morphological changes were also detected at the highest concentration of MC, but no changes in fluorescence intensity were noticed. The results show that cyanotoxins do not inhibit the growth of C. reinhardtii at concentrations common in freshwater, although they may affect other microalgae in aquatic ecosystems, which show different resistance to cyanotoxins. Additionally, cyanotoxins may act synergistically with each other or with other substances in nature.
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