1. Department of Microbiology, GBF-National Research Centre for Biotechnology,D-38124 Braunschweig, Germany2
2. Department of Microbiology and Biotechnology, University of Ulm, D-89069 Ulm, Germany1
3. Bayer AG, PH Research Antiinfectives I, D-42096 Wuppertal, Germany3
4. Institute for Organic Chemistry, University of Tübingen, D-72070 Tübingen, Germany4