1. Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen (GBB), Kerklaan 30, 9751 NN Haren, The Netherlands
2. Netherlands Institute of Ecology (NIOO-KNAW), Postbus 140, 4400 AC Yerseke, The Netherlands
3. Laboratory of Microbiology, Wageningen University, Hesselink van Suchtelenweg 4, 6703 CT Wageningen, The Netherlands