SECONDARY FUNGAL METABOLITES AND THEIR BIOLOGICAL-ACTIVITIES, .5. 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 to xic 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 toxi ns which are synthesized already in monocultures in very low concentra tions. After excretion and diffusion into the media, the fungi thus re cognize the proximity of the antagonist in dualcultures. As a conseque nce, the enormous stimulation of toxin synthesis takes place. The incr easing 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 to xin synthesis is achieved by an enhanced de novo synthesis of enzymes of the corresponding secondary pathways.