Chemical defence by mono-prenyl hydroquinone in a freshwater ciliate, Spirostomum ambiguum

Several species of ciliates produce and accumulate low molecular weight toxic compounds in specialised membrane-bound ejectable organelles: extrusomes. These compounds can be used in predator–prey interaction for killing prey as well as for chemical defence. Here, we describe the isolation and characterisation of 2-(3-methylbut-2-enyl)benzene-1,4-diol(mono-prenyl hydroquinone), the extrusomal defensive toxin of the freshwater heterotrich ciliate Spirostomum ambiguum. The toxin was purified at homogeneity by RP-HPLC, and its structural characterisation was carried out through NMR and MS measurements. In vivo experiments involving S. ambiguum and Climacostomum virens in predator–prey interaction, and the analysis of cytotoxic activity of mono-prenyl hydroquinone on a panel of free-living freshwater ciliates, indicated that the toxin is very effective in S. ambiguum’s chemical defence.