1. Laboratory of Microbial Ecology and Technology, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium, Laboratory of Non-Ferrous Metallurgy, Ghent University, Technologiepark Zwijnaarde 914, B-9052 Zwijnaarde, Belgium, and Environmental Technology Department, Wageningen University, Wageningen, NL-6700 EV, The Netherlands