1. Unit of Bioengineering, Université Catholique de Louvain, Place Croix du Sud 2/19, B-1348 Louvain-la-Neuve, Belgium, Laboratory of Microbial Ecology, University of Ghent, Coupure Links 653, B-9000 Ghent, Belgium, and Laboratory of Microbial Genetics, Université Catholique de Louvain, Place Croix du Sud 5/12, B-1348, Louvain-la-Neuve, Belgium