1. CEA/Cadarache, DSV-DEVM, Laboratoire d'Ecologie Microbienne de la Rhizosphère, UMR 163 CNRS-CEA, F-13108 Saint-Paul-lez-Durance, France,1 and
2. Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, 3584 CH Utrecht, The Netherlands2