Interfakultäres Institut für Mikrobiologie und Infektionsmedizin

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Research Areas

The Fiedler Group consists of the project leader apl. Prof. Dr. Hans-Peter Fiedler, the fermentation engineer Dipl. Ing. Andreas Kulik, diplome and doctoral students, and non-permanent additional scientific and technical staff sponsored by various national and international grants. The main interest of the group is focused to the detection of novel bioactive secondary metabolites produced by new isolated actinomycete strains with the aim for clinical use as antiinfective or anticancer drugs, and for agricultural use as fungicides, insecticides or hebicides. Following topics are under investigation:

Isolation of new actinomycetes strains and taxonomic characterization

Various selective and non-selevtive methods are applied to isolate actinomycetes from soils and sediments from various habitats. Marine sources are of special interest, such as sediments from deep sea trenches from the Pacific and Atlantic Ocean. Besides the well known families Streptomycetaceae and Micromonosporaceae, members of rare actinomycete genera are isolated for screening purposes. The new isolates are determined by morphological and chemotaxonomical methods and 16S rDNA sequencing to the genus level. The actinomycete collection of the group contains 1100 terrestrial and 800 marine actinomycete strains.

HPLC-DAD screening for novel secondary metabolites

Extracts from new isolated actinomycete strains are cultivated in the shake flask scale and extracts are prepared from biomasses and culture filtrates to determine the chemical diversity by means of our HPLC-UV-Vis-Database. The equipment of the group consists of three fully automated HP 1090 liquid chromatographs with diode array monitoring and rapid ChemStations.

Scale-up fermentation and metabolite isolation

The group is equipped with eight fermenters in the scale 1-8 litres, eleven fermenters in the scale 10-20 litres, one airlift fermenter with 3.5 litre working volume, and one dialysis fermenter. All reactors can be used in the batch or fed-batch mode. One 100 litre stirred tank fermenter (P-100, BioEngineering) and one 200 litre intensor fermenter (b200, Giovanola) are availabel for the production scale.

Metabolite isolation from the biomass is done by solvent extraction and from the culture filtrate by polystyrene resin chromatography (Amberlite XAD, Diaion Sepabeads). A specific purification protocol is developed in case of each metabolite dependent on its hydrophilic or lipophilic properties. Polar metabolites are purified by subsequent ion-exchange chromatographic steps (anion/cation exchange) followed by aqueous size exclusion chromatography. Lipophilic metabolites are purified by adsorption chromatography (silica gel, diol modified silica gel), size exclusion chromatography (Sephadex, Toyopearl) and preparative reversed-phase HPLC. The isolation steps are evaluated by HPLC-DAD analysis and biological assays.

Biological evaluation

A set of antibacterial, antifungal, herbicidal and phytotoxic tests based on agar-plate diffusion assays are applied for determination of biological activity spectra, and micro-titer plate based assays for determining minimal inhibition concentrations. Investigations in mode of action are done in case of promising drug candidates.