The HP Fiedler Group

The HP Fiedler Group has been disbanded due to the retirement of Professor Hans-Peter Fiedler, the leader of the research group, at 1st August 2012. Nevertheless, the homepage is kept still active to acknowledge the essential contributions of his post-docs, doctoral and diplome students, and the technical staff during the fruitful period of 24 years. Thanks, the same to his colleagues from various universities and chemical-pharmaceutical companies which contributed within national and international collaborations mainly to the success in screening of microbial strains, determining biological activities and structure elucidation of the isolated microbial metabolites.

The main interest of the group was focused to the discovery 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 herbicides. Following topics were investigated:

Isolation of new actinomycetes and taxonomic characterization

Various selective and non-selective methods were applied to isolate actinomycetes from soils and sediments from various habitats. Marine sources were 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 were isolated for screening purposes. The new isolates were determined by morphological and chemotaxonomical methods and 16S rDNA sequencing to the genus level. The actinomycete collection of the group contained 1100 terrestrial and 800 marine actinomycete strains.

Rhodococcus spec.Nocardia spec. nov.Verrucosispora maris

Rhodococcus spec. | Nocardia spec. nov. | Verrucosispora maris

HPLC-DAD screening for novel secondary metabolites

Extracts from new isolated actinomycete strains were cultivated in the shake flask scale and extracts were prepared from biomasses and culture filtrates to determine the chemical diversity by means of our HPLC-UV-Vis-Database. The equipment of the group consisted of four fully automated HP 1090 liquid chromatographs with diode array monitoring and rapid ChemStations. The group had access to HPLC-DAD-ESI-MS analysis with an Agilent 1200 series and LC/MSD Ultra Trap 6330.

Left: HP 1090 liquid chromatograph (HPLC-DAD), right: Agilent 1200 LC-MS

HP 1090 Liquid chromatograph (HPLC-DAD) | Agilent 1200 LC-MS

Scale-up fermentation and metabolite isolation

The group was equipped with eight fermentors in the scale 1-8 litres, and seven fermentors in the scale 10-20 litres. All reactors could be used in the batch or fed-batch mode. A 100 litre stirred tank fermentor (P-100, BioEngineering) was available for the production scale.

Left: Home made 500-ml mini-fermentor, middle: 10-liter fermentor Biostat E, right: 100 liter fermentor P-100
Home made 500-ml mini-fermentor | 10-liter fermentor Biostat E | 100 liter fermentor P-100

Metabolite isolation from the biomass was done by solvent extraction and from the culture filtrate by polystyrene resin chromatography (Amberlite XAD, Diaion Sepabeads). A specific purification protocol was developed in the case of each metabolite dependent on its hydrophilic or lipophilic properties. Polar metabolites were 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 were 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 were applied for determination of biological activity spectra, and micro-titer plate based assays for determining minimal inhibition concentrations. Investigations in mode of action were done in the case of promising drug candidates.