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

Abstract

Summary1. 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.

Pack hunting by a common soil amoeba on nematodes

“…More sophisticated evidence for intraguild interactions between protists and nematodes has recently been reported (Bjørnlund and Rønn, ; Neidig et al ., ). Neidig and colleagues () showed that exoproducts of amoebae repelled nematodes and exhibited marked nematostatic activity, while exoproducts of nematodes increased encystation and reduced growth of their bacterivore competitors.…”

“…More sophisticated evidence for intraguild interactions between protists and nematodes has recently been reported (Bjørnlund and Rønn, ; Neidig et al ., ). Neidig and colleagues () showed that exoproducts of amoebae repelled nematodes and exhibited marked nematostatic activity, while exoproducts of nematodes increased encystation and reduced growth of their bacterivore competitors. Likewise Bjørnlund and Rønn () found flagellates that killed nematodes at high flagellate abundance, whereas nematodes consumed flagellates at lower densities; however, neither flagellates nor nematodes benefited from this trophic interaction under any of the experimental conditions.…”

“…In contrast, direct feeding of more abundant smaller‐sized protists (body < 20 μm in diameter) on larger‐sized nematodes (body > 250 μm in length) is not yet known. However, evidence obtained in liquid microcosm studies similar to those used in our approach revealed that unclassified tiny protists might affect nematode behaviour (Bjørnlund and Rønn, ; Neidig et al ., ). All these studies suggest that the trophic positions of protists cannot be restricted into a single role like ‘bacterivores’ and even feeding on larger organisms such as nematodes might be common among soil protists.…”

Ecological importance of soil bacterivores for ecosystem functions

“…Recent studies indicate that intraguild-predation between 'bacterivores', especially antagonistic interactions between protists and nematodes are quite common and not unidirectional (Geisen et al 2014;Geisen et al 2015). Bacterivore nematodes are known to prey on protists Bonkowski et al 2000;Neidig et al 2010;Rønn et al 2012) and vice-versa (Bjornlund and Rønn 2008;Neidig et al 2010). The population density of one bacterivore taxon can thus increase on the cost of other another bacterivore (Anderson and Coleman 1981).…”

Phagotrophic Protists and Their Associates: Evidence for Preferential Grazing in an Abiotically Driven Soil Ecosystem

“…Phagotrophic protists are an integral component of virtually all soil communities and possess a diverse suite of cell morphologies and functional traits that allow species to consume a variety of prey from a range of soil pore sizes [ 3 , 4 , 5 ]. They are especially known for promoting bacterial diversity and mobilizing nutrients (as prey) to higher trophic tiers [ 6 , 7 , 8 , 9 ], as well as regulating the populations of fungi, some metazoa, and other protists through predation and competition [ 10 , 11 , 12 ]. Currently, soil phagotrophic protist functions are generalized from studies of in vitro systems involving only a few, easily cultured taxa and artificially depauperate microbial communities [ 13 , 14 , 15 ].…”