• Nematode-trapping fungus;
  • peptide-induced/amino acid-induced morphogenesis;
  • synchronous trap formation

Abstract The nematode-trapping fungus Arthrobotrys oligospora was grown in liquid culture in modified separatory funnels with vigorous air bubbling. The growth medium was a dilute soya peptone broth supplemented with a trap-inducing substance. The dipeptide l-phenylalanyl-l-valine or its constituents phenylalanine and valine were used as inducers of trap formation. Trap formation started within 2 days after inoculation and the traps increased in number and size during a 7-day period. The traps formed in liquid culture were fully functional in trapping nematodes. At the ultrastructural level they were characterized by the presence of many electron-dense microbodies similar to those in trap cells grown on solid media. Biomass increase, amounting to 6–7 mg dry weight · ml−1, and trap formation were highly synchronized. The mycelial mass was homogeneously dispersed in the growth vessel during the entire growth period. Heavy trap formation in liquid culture by this fungus has not been reported previously.