1. Institute of Microbiology, Eidgenössische Technische Hochschule (ETH), Zürich, Vladimir-Prelog-Weg 4, 8093 Zürich, Switzerland
2. Department of Molecular Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 7, 9747, AG Groningen, The Netherlands