Interference between bacterial feeding nematodes and amoebae relies on innate and inducible mutual toxicity

Abstract

P>1. Protozoa and nematodes are important microfauna predators in soil and compete for the same food resource, bacteria. Therefore, inhibition of competitors may enhance food acquisition and fitness of individual predator species. 2. We investigated chemical based interference between the nematode Caenorhabditis elegans and the amoeba Acanthamoeba castellanii in a bacteria-free gnotobiotic system. 3. Exoproducts of amoebae exhibited marked nematostatic activity, and repelled the worms. However, nematodes were able to reduce the activity of proteases and glycosidases, two enzymes playing an important role in the toxicity of A. castellanii. Exoproducts of nematodes also detrimentally affected amoebae by reducing growth and increasing encystation. 4. The results indicate that both protozoa and nematodes can inhibit each other, and that nematodes are also able to counteract the attack by protist competitors. Non-trophic interactions appear thus as a new factor affecting the structure of predator communities in soil.