1. Department of Fundamental Microbiology, University of Lausanne, CH-1015 Lausanne, Switzerland
2. INRA-INAPG, 78850 Thiverval Grignon, France
3. Department of Genetics, Faculty of Biology, Bielefeld University, D-33594 Bielefeld, Germany
4. Swiss Federal Institute of Aquatic Science and Technology (Eawag), CH-8600 Dübendorf, Switzerland