1. Department of Civil Engineering, Northwestern University, Evanston, Illinois 60208-31091;
2. Max-Planck-Institute for Marine Microbiology, D-28359 Bremen, Germany2;
3. The Moshe Shilo Center for Marine Biogeochemistry, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel3; and
4. Technische Universität München, Lehrstuhl für Mikrobiologie, D-80290 Munich, Germany4