1. Department of Marine Microbiology, University of Bremen, Leobener Strasse, 28359 Bremen, Germany, Unit of Bioengineering, Catholic University of Louvain, Place Croix du Sud, 2 Bt 19, 1348 Louvain-la-Neuve, Belgium, and Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands