1. Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany
2. CNRS and Université Montpellier II UMR 5119, Case 093, Place Eugène Bataillon, F-34095 Montpellier Cedex 05, France
3. Delft University of Technology, Postbox 5048, NL-2600 GA Delft, The Netherlands