The genes for the synthesis of natural products in Aspergillus nidulans are localized in specific gene clusters. The regulation depends mainly on their environmental conditions e.g. competing microorganisms and availability of different nutritional sources. In this respect the natural environment differs strongly from the conditions in biotechnological fermentation processes, which can lead to a partially silence of interesting gene clusters. In this respect the project is directed to the investigation of the regulation of specific gene clusters of secondary metabolites in dependence on interactions with competing microorganisms.