Trap formation in A. oligospora could be caused by bacterial metabolites that are released into the environment. To test whether diffusible low-molecular-weight signalling molecules triggered fungal trap formation, we treated the fungal culture with the supernatant of the bacterial culture as well as heat-inactivated bacteria. In no case was the fungal trap formation observed. Obviously, the induction of traps in fungi depends on the direct contact between the fungus and the bacterium. This assumption was unambiguously confirmed by SEM of fungal hyphae obtained from cocultivation. In soil, many bacteria and fungi will often occupy a shared microhabitat, called the bacterial–fungal interface (Johanssonet al.,2004). Traditional studies have shown the presence of bacterial cells at the interface, for example on top of fungal hyphae and spores, on mycorrhized roots and in association with fungal fruiting bodies (de Boeret al.,2005). Only one study showed some bacteria associated with A. oligospora ORS 18692 S7 and could enhance fungal activity against the nematode, but the mechanisms were unknown (Duponnoiset al.,1998). The mechanisms by which Chryseobacterium sp. TFB-induced traps in A. oligospora are being investigated.