1. Department of Biology, Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Schafmattstrasse 20, CH-8093 Zürich, Switzerland
2. Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
3. Institute of Microbiology, Eidgenössische Technische Hochschule (ETH), CH-8093 Zürich, Switzerland