Capture of nematodes by Arthrobotrys oligospora, an electron microscope study

Abstract

The capture of nematodes by Arthrobotrys oligospora consists of (1) firm adhesion of the nematode to the capture organ, (2) penetration of the nematode cuticle by a penetration hypha, and (3) digestion of the nematode. Penetration of the nematode cuticle by a penetration hypha originating from the trap took place within 1 h after addition of nematodes to a fungal culture and occurred at any point on the nematode surface. Vegetative hyphae were able to invade an immobilized nematode only through the body orifices (8–12 h after addition of nematodes to fungal cultures lacking traps). The presence of prey caused an increased secretion of adhesive from the trap. Scanning electron microscope micrographs show a captured nematode covered by a mucilaginous coat. In transmission electron microscope micrographs of thin sections, a distinct osmiophilic layer between trap and nematode is always present. Since penetration occurred at the point of deposit of these substances, it is suggested that the osmiophilic layer also has enzymatic activity. An osmiophilic layer was never seen around vegetative hyphae, indicating the lack of both adhesive and similar enzymes.The traps contained numerous membranous electron-dense vesicles (150–300 nm) not present in hyphae. Large osmiophilic inclusions (1–2 μm) were more common in traps at certain stages of development than in hyphae. The results indicate that the adhesive and the digestive enzymes originate from either or both of these organelles.