1. Institute of Physiology and Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Winterthurerstrasse 190, Zürich, Switzerland.
2. Department of Biology, University of Konstanz, Universitätsstrasse 10, M647, D-78457 Konstanz, Germany.
3. Institute of Microbiology, Swiss Federal Institute of Technology (ETH), Zürich, Switzerland.