Secondary metabolites with nematicidal and antimicrobial activity from nematophagous fungi and Ascomycetes

Abstract

Screening of nematode-trapping fungi for antimicrobial and nematicidal activities gave three new antimicrobial metabolites from cultures of five Arthrobotrys strains. The compounds exhibited no nematicidal activities towards Caenorhabditis elegans and Meloidogyne incognita. From trap-forming submerged cultures of Arthrobotrys conoides, linoleic acid was isolated as a nematicidal principle. Its production increased with the number of traps formed in both Arthrobotrys oligospora and Arthrobotrys conoides. Nematoctonus robustus and Nematoctonus concurrens produced pleurotin, dihydropleurotinic acid, and leucopleurotin, metabolites previously isolated from cultures of Hohenbuehelia species, suggesting that the same biosynthetic pathways function in both the teleomorph and anamorph. Several strains of Ascomycetes had nematicidal activities; linoleic acid was responsible for the activity in cultures of a Chlorosplenium species, 14-epicochlioquinone B in cultures of Neobulgaria pura, and two naphthalenes derived from the melanin biosynthetic pathway in Daldinia concentrica. 5-Pentyl-2-furaldehyde, previously known as a metabolite from a Basidiomycete, was produced by an unidentified Australian Ascomycete. More than 30 mostly new metabolites have been isolated from cultures of Lachnum papyraceum, many being chlorinated. Under different conditions the fungus incorporated bromine instead of chlorine. Key words: nematophagous fungi, natural nematicides, linoleic acid, chlorinated secondary metabolites.