PREDACIOUS ACTIVITY OF THE NEMATODE-DESTROYING FUNGUS ARTHROBOTRYS-OLIGOSPORA IN DEPENDENCE OF THE MEDIUM COMPOSITION

The nematophagous fungus Arthrobotrys oligospora Fres. can live saprop hytically as well as predatorily. As a predator it forms sticky reticu late traps in the presence of living nematodes which enable it to kill and consume the animals. In laboratory experiments the nutrient acqui sition of the fungus was tested on agar media with various N- and C-so urces in different concentrations. The intensity of predacious respons e was determined by counting the traps formed on the agar surface afte r induction by nematodes. Predacious activity (PA) served as a unit of the strength of nematophagous response. PA was defined as the number of traps/100 mm2. In contrast to carnivorous higher plants, which cons ume insects in order to compensate their N-deficit, the fungus seems t o kill nematodes to get both, N as well as C. If the agar substrate co ntains a certain concentration of N and C, the fungus does not form tr aps and lives as a saprophyte. The level which determines the switch t owards pure saprophytism under laboratory conditions ranges around 0.1 2 M C at a N-concentration of 0.05 M. If no nitrogen is added to the m edium the fungus forms nematode-induced traps even in the most concent rated C- media. On N-media without any carbon source the fungus shows a much stronger PA compared with N-free media. Furthermore, more chlam ydospores were formed on N media.