Isolation structure elucidation and characterization of bacterial siderophores In this thesis a genome mining approach including bioinformatic predictions of natural product biosynthesis gene clusters was used to detect and isolate putative siderophores (small molecule iron transporters) from underexplored ß proteobacteria. In the first part of this study the novel iron chelating lipopeptides cupriachelin from Cupriavidus necator and taiwachelin from Cupriavidus taiwanensis were discovered and chemically analyzed. Both natural products showed iron dependent photoreactivity when exposed to sunlight. In course of the photodissociation Fe(III) is reduced to highly soluble Fe(II). A reaction which might be important for the ecological iron cycling in aqueous habitats. The second part of this study is focused on the biosynthesis of the antimycoplasma agent micacocidin from the plant pathogen Ralstonia solanacearum. Dissection of an unusual polyketide synthase module helped identifying the assembly process of the aromatic starter unit 6 pentylsalicylic acid. Moreover it could be shown that the iterative type I polyketide synthase is tolerant towards incorporation of unnatural starter units. A precursor directed biosynthesis led to the isolation of numerous micacocidin derivatives with promising