1. Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
2. Max Planck Institute for Molecular Genetics, Berlin, Germany
3. Present address: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
4. Functional Genomics Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland
5. Institute of Food, Nutrition and Health, ETH Zurich, Zurich, Switzerland