Harmful cyanobacteria and its toxic metabolites microcystin and saxitoxin in freshwater lakes of Southeast Norway.
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Harmful cyanobacteria are a globally growing concern due to global warming and eutrophication. Cyanobacteria are capable of producing a variety of cyanotoxins, which could be harmful to animals and human health. In this study, the presence of cyanobacteria and its toxic metabolites microcystin and saxitoxin were investigated in six freshwater lakes in Vestfold, Southeast Norway, by using microscopic- , immunological- (ELISA) and molecular techniques (PCR). Cyanobacteria were detected in 11 out of 12 samples. Dolichospermum was the most frequently occurring genera, while Microcystis was the most abundant. Even though one lake showed N-limitation, which could favour the growth of N-fixing cyanobacteria, the lake was dominated by Microcystis, probably due to the high total concentrations of N and P. Microcystin and saxitoxin were detected in 8 and 4 samples, respectively, concentrations of microcystins ranging from 0,7-32,2 µg/L and saxitoxin from 0,05 to 0,146 µg/L. The mcyE gene was detected in five samples, while the sxtA gene was detected in only one sample. In all samples where mcyE and sxtA were detected, microcystin and saxitoxin were also detected. Even though microcystin and saxotoxin were detected in samples without mcyE/sxtA as well, there seemed to be a positive correlation between toxin concentration and gene detection. Based on microscopic findings and toxin- and gene-detection, there is a strong indication that the likely candidates responsible for microcystin and saxitoxin production in the samples belonged to the genera Microcystis and Dolichospermum, respectively.