Mechanical and chemical interactions in offense-defense strategies of freshwater ciliates.

In the past 30 years a number of studies have been devoted to analyzing the morphological and molecular basis of predator–prey interactions in ciliates, and particular attention was focused on the important role of specialized ejectable membrane-bound organelles, generally called extrusomes, in the immobilization and capture of prey, and in defense from predators. There are, essentially, two types of strategies adopted in predator–prey interactions among ciliates: 1) the first mediated by mechanical mechanisms involving trichocysts, the subpellicular non-toxic extrusive organelles, used for defense by some ciliates such as Paramecium, Frontonia or Pseudomicrotorax; 2) the second mediated by secondary metabolites (contained in different kinds of chemical extrusomes) used for offense or defense by other ciliates (such as Bepharisma, Climacostomum or Spirostomum). These interactions are, until now, mainly studied in unicellular predators-prey models. Here we report the defensive function of trichocysts in Paramecium tetraurelia against three metazoan predators and we compare the defensive efficiency of these mechanical extrusomes with that of chemical extrusomes in two toxic ciliates (Climacostomum virens and Spirostomum ambiguum). The results prove the defensive function of trichocysts against two of these metazoan predators (Cephalodella sp., Rotifera and Eucypris sp., Arthropoda) while they seems ineffective against S. sphagnetorum (Platyhelminthes). In addition, with regards of chemical extrusomes in ciliates, we analyze the content of the cortical granules of the heterotrich ciliate S. ambiguum, represented by mono-prenyl hydroquinone, and for the first time, the content of the toxicysts (offensive extrusomes) of a predatory ciliate, the protostomatid Coleps hirtus. The data collected for this ciliate show the chemical composition of the toxicysts content as a free fatty acid mixture mainly represented by PUFAs, together with the presence of two diterpenes.