New Bioactive Secondary Metabolites From Nematode-associated Fungi

Biological pest control is becoming increasingly important because agrochemical pesticides and soil fumigants are being banned for their negative influence on biodiversity. Invertebrate pathogens that are attacking the roots or living underground, have always been difficult to control with pesticides, anyway. We have studied new candidate strains that were isolated from nematode eggs and cysts for their taxonomy and secondary metabolite production. These ascomycetes were isolated from diseased eggs and cysts of nematodes that parasitize the rhizosphere of agricultural crops. Aside from known nematode antagonists like Pochonia spp., several new species of other hypocrealean genera (e.g. Ijuhya, Niesslia) were encountered. In addition, several strains were found that have affinities to the “dark septate root endophytes”. The new genera Polydomus (Phaeosphaericeae, Dothideomycetes) and Polyphilus (Helotiales, Leotiomycetes) were erected to accommodate those strains, and another species was placed in the pleosporealean genus Laburnicola.

In parallel, these ecologically and biotechnologically interesting fungi were subjected to an in-depth study of their secondary metabolites. Numerous compounds were isolated by preparative chromatography and identified by spectral methods from their cultures. We have obtained over 20 new natural products, including some new carbon skeletons. The pure compounds were studied for their antimicrobial, cytotoxic, nematicidal and other biological effects. 

The outcome of this project shows that ecologically interesting fungi are an extremely rich source of innovative chemistry. Moreover, it is essential for the registration of new biocontrol agents that the candidate strains do not produce dangerous mycotoxins. Hence, our work is part of the risk assessment.