1. Department of Ecology and Evolution, University of Lausanne, Lausanne CH-1015, Switzerland
2. Department of Biology, Stanford University, Stanford, California 94305-5020
3. School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland
4. Genomic Medicine, The J. Craig Venter Institute, 4120 Capricorn Lane, La Jolla, California 92037
5. Institute of Microbiology, University Hospital and University of Lausanne, Lausanne CH-1011, Switzerland