Conidial trap formation of nematode-trapping fungi in soil and soil extracts

Abstract

Conidial traps (CT) in nematode‐trapping fungi are trapping structures formed directly on germination of conidia, without an intermediate hyphal phase. Most of the nine fungi tested were able to form CT on water agar surfaces in the vicinity of soil, but the ability varied between species. Generally, the ability to form CT was greatest in Arthrobotrys dactyloides and Monacrosporium gephyropagum followed by Arthrobotrys superba and Arthrobotrys oligospora. The mechanism behind CT formation was further studied in soil extracts using a microwell plate assay. Preincubation of soil or soil extracts at room temperature before inoculation with conidia increased the incidence of CT. Reduction of the number of microorganisms in soil extracts by sterile filtration, dilution or heating decreased CT formation, as did the addition of nutrients. The results suggest that a certain level of competition for nutrients by microorganisms is necessary for CT formation. In contrast, we were unable to induce CT when conidia were allowed to germinate in pure culture on hyphal trap‐inducing or non‐inducing agar media with or without cell wall affecting compounds.

Morphogenesis in the nematode-trapping fungus Arthrobotrys oligospora - an extensive plasticity of infection structures

“…This result indicates competition for nutrients by microorganisms as being one of the reasons for conidia germinating directly into traps, thus overcoming fungistatic conditions in soil. Furthermore, rhizosphere soil was more efficient than root-free soil (Persmark & Nordbring-Hertz, 1997). It remains to be shown whether conidial traps develop in the vicinity of living roots.…”

“…Alternatively, traps may be formed directly upon germination without an intermediate hyphal phase to form so-called conidial traps (CTs). These structures were found in natural environments such as cow dung (Dackman & Nordbring-Hertz, 1992) and rhizosphere soil (Persmark & Nordbring-Hertz, 1997). In these environments CTs were detected not only in A. oligospora but also in several other nematode-trapping fungi (Barron, 1977;Dowe, 1987;Persmark & Nordbring-Hertz, 1997).…”

“…Conidial traps were observed in all but one species but the ability varied between species, with A. dactyloides and Monacrosporium gephyropagum being more efficient than A. superba and A. oligospora (Fig 6;Persmark & Nordbring-Hertz, 1997).…”

How carnivorous fungi use three-celled constricting rings to trap nematodes

“…Traps are usually produced from hyphae but can also be produced by germinating conidia, especially in the case of fungi that produce constricting rings (Persmark and Nordbring-Hertz, 1997). The production of traps by germinating conidia presumably minimizes the resources and time required by the fungus to begin to compete for nitrogen (Dackman and Nordbring-Hertz, 1992).…”

Trap Induction and Trapping in Eight Nematode-trapping Fungi (Orbiliaceae) as Affected by Juvenile Stage of Caenorhabditis elegans

“…The nematodetrapping fungi can be induced to form traps by substances such as sterile filtrate of nematode cultures, human blood serum, extracts from earthworms, CO 2 , cellophane, small peptides, lectins, cow feces, soil, and soil extracts [4,[9][10][11][12][13][14]. Nordbring-Hertz [15] showed that the direct contact of living nematodes with hyphae was very effective at inducing traps and was more effective than peptides.…”