1. Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9751 NN Haren, The Netherlands
2. Department of Biology, University of Bergen, Jahnebakken 5, Box 7800, N-5020 Bergen, Norway
3. Institute of Biochemistry, Biozentrum Frankfurt, Johann Wolfgang Goethe University, Marie-Curie-Strasse 9, 60439 Frankfurt am Main, Germany
4. Institute for Microbiology and Genetics, Darmstadt University of Technology, Schnittspahnstr. 10, 64287 Darmstadt, Germany