1. Research Group of Industrial Microbiology, Fermentation Technology and Downstream Processing, Department of Applied Biological Sciences, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium1
2. Laboratory of Microbial Gene Technology, Department of Biotechnological Sciences, Agricultural University of Norway, Post Box 5051, N-1432 Ås, Norway2
3. Laboratory of Protein Biochemistry and Protein Engineering, Faculty of Sciences, Universiteit Gent, K. L. Ledeganckstraat 35, B-9000 Gent, Belgium3