Chemical Defence by Sterols in the Freshwater Ciliate Stentor polymorphus

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.

Editorial for the Special Issue, ‘Secondary Metabolites from Microorganisms or Microorganism–Host Interaction?’

“…The chemical defense strategy of the sterol Stentor polymorphus against Coleps hirtus has been reported. The isolated and identified sterols are essential for chemical defense in S. polymorphus [4]. Motility, stress, and virulence from Escherichia coli associated with tomato fruits have been investigated; this paper provides new information on the physiological adaptation of bacteria colonizing the tomato fruit pericarp [5].…”