1. Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, 9000 Gent, Belgium, Department of Environmental Engineering, Technical University of Denmark (DTU), Miljoevej, Building 113, 2800 Kgs. Lyngby, Denmark, and Department of Chemical Engineering, School of Engineering, University of Santiago de Compostela, Rúa Lope Gómez de Marzoa s/n, 15782 Santiago de Compostela, Spain