Factors responsible for transition of the Duddingtonia flagrans carnivorous fungus from the saprotrophic to the zootrophic nutrition type

Quantitative investigation of the factors responsible for trap formation in the nematophagous fungus Duddingtonia flagrans F-882 in submerged liquid culture was carried out. The data obtained suggest a complex program for the regulation of zootrophic nutrition in D. flagrans. Optimal concentrations of such carbon and nitrogen sources as sucrose (0.4%), ammonium ions (0.2%), and tryptone (0.2%) promote trap formation in the case of contact with the nematodes Panagrellus redivivus. Increased concentrations of these compounds, however, inhibit trap formation. The sensitivity of the mycelium to nematode excreta depends on the state of the culture and is increased under limitation by certain nutrient components or in the course of prolonged starvation. A direct correlation was found between the number of caught nematodes and the number of chlamydospores formed on the mycelium. The nutrients obtained from the nematode biomass are used for formation of additional chlamydospores (on average, about 20 chlamydospores per nematode). Environmental and evolutionary aspects of the role of zootrophic nutrition in carnivorous fungi are discussed.