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Updated: Aug 16, 2025

A Fish-feeding Laboratory Bioassay to Assess the Antipredatory Activity of Secondary Metabolites from the Tissues of Marine Organisms
Published on: January 11, 2015
Chemical Defence by Sterols in the Freshwater Ciliate Stentor polymorphus
Federico Buonanno1, Francesco Trenti2, Gabriele Achille1
1Laboratory of Protistology and Biology Education, Department of Education, Cultural Heritage, Tourism (ECHT), University of Macerata, 62100 Macerata, Italy.
Abstract:
Heterotrich ciliates typically retain toxic substances in specialized ejectable organelles, called extrusomes, which are used in predator-prey interactions. In this study, we analysed the chemical defence strategy of the freshwater heterotrich ciliate Stentor polymorphus against the predatory ciliate Coleps hirtus, and the microturbellarian flatworm Stenostomum sphagnetorum. The results showed that S. polymorphus is able to defend itself against these two predators by deploying a mix of bioactive sterols contained in its extrusomes. Sterols were isolated in vivo and characterized by liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR), as ergosterol, 7-dehydroporiferasterol, and their two peroxidized analogues. The assessment of the toxicity of ergosterol and ergosterol peroxide against various organisms, indicated that these sterols are essential for the effectiveness of the chemical defence in S. polymorphus.
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