Effect of fractions of toxic cyanobacterium, Nodularia spumingena KAC 66 and its purified nodularin and nodulopeptin 901 on inhibition of colorimetric protein phosphatase 1 assay and lethality against two species of Daphnia

The strains of Nodularia are known to produce potent hepatotoxic nodularins (NOD) and other bioactive metabolites i.e. nodulopeptins and spumigins. Contemporary, three new nodulopeptins were also isolated from N. spumigena KAC 66 collected from the Baltic Sea. The wide distribution and toxicological effects of N. spumigena on food chain, has caused significant attention towards the effects of the species. In the present investigation the toxicity of NOD and nodulopeptin 901, produced by N. spumigena, was fractionated by Reversed Phase Flash Chromatography (RPFC) and their toxicity was determined by their lethality to water fleas, Daphnia pulex and D. magna along with inhibition of protein phosphatase 1 assay (PP1; eukaryotic threonine phosphatase/protein serine). All fractions showed lethality to Daphnids and inhibitory activity against PP1, the toxicity was due to additional compounds as NOD and nodulopeptin 901 were only detected in 7 fractions. The pure NOD was lethal to D. pulex and D. magna LC50=8.4 µg. ml-1 and 5.0 µg .ml-1, respectively. The newly characterized nodulopeptin 901 was also tested against D. magna (LC50=>100 µg .ml-1). NOD and nodulopeptin 901 inhibited PP1 with weak IC500.038 μg .ml-1 and 25 µg .ml-1, respectively. The anabaenopeptin A (ANA) and anabaenopeptin B (ANAB) were used as reference peptides as they have similarity in structure with newly characterized nodulopeptin 901. The ANA, ANB and linear nodularin (LNOD) inhibited PP1 with IC5070μg .ml-1,100μg .ml-1 and20μg .ml-1, correspondingly. This is the first study that indicates the toxic and inhibitory activities of nodulopeptin 901 and fractions of N. spumigena KAC 66 against daphnids and PP1.