Secondary fungal metabolites and their biological activities, V. Investigations concerning the induction of the biosynthesis of toxic secondary metabolites in basidiomycetes.

In cultures of the basidiomycetes Heterobasidion annosum, Gloeophyllum abietinum or Armillaria ostoyae, the biosynthesis of some of their toxic secondary metabolites is enhanced up to 400-fold when they grow in the presence of an antagonist. This stimulation is induced before any cell contact occurs. The "inducing signals" are not macromolecules, polypeptides or constituents of the cell membranes, but the same toxins which are synthesized already in monocultures in very low concentrations. After excretion and diffusion into the media, the fungi thus recognize the proximity of the antagonist in dualcultures. As a consequence, the enormous stimulation of toxin synthesis takes place. The increasing toxin concentrations in the fungal dual cultures finally cause the formation of mycel-free growth inhibition zones between the fungi, or sometimes one of the contrahents is killed. This stimulation of toxin synthesis is achieved by an enhanced de novo synthesis of enzymes of the corresponding secondary pathways.