Self-recognition as the original function of an amoeban defense-inducing kairomone

A 4.5 kg/mol peptide released by an amoeban predator, Amoeba proteus, induc ed defensive behavioral changes in ciliates of the genus Euplotes. The inte rspecific signaling molecule named "A-factor" was present in amoebae cultur e medium at a concentration of 0.01 mu g peptide/L, corresponding to 2 x 10 (-12) mol/L. Amoebae released similar to 3 x 10(5) molecules of A-factor pe r individual per hour. Prey ciliates added to solutions containing A-factor exhibited predator-avoidance behavior after a few hours. The discovery of a second function for this peptide-kairomone indicated why the predator bet rays its presence to the prey and thereby unintentionally protects it. Inhi bition of phagocytosis by particle-bound kairomone revealed that it also fu nctions as a self-recognition signal in the predator. Phagocytosis of parti cles by amoebae depended on the amount of A-factor on the particle surface and decreased in linear correlation to the logarithm of peptide amount. Sel f-recognition prevents a mutual consumption of amoebae, leading to increase d survival of these asexually reproducing organisms. The importance of self -recognition apparently outweighs the disadvantages of defense induction, s ince only few prey species of the omnivorous predator respond in this manne r.