1. Laboratory of Microbiology, Wageningen University, Stippeneng 4, Building 124, 6708 WE Wageningen, the Netherlands
2. VIB Lab for Bioinformatics and (Eco-)systems Biology, KU Leuven, Campus Gasthuisberg, 3000 Leuven, Belgium
3. Department of Mathematics and Statistics, University of Turku, 20014 Turku, Finland
4. Research Programme Unit Immunobiology, Department of Bacteriology and Immunology, Helsinki University, P.O. Box 21, 00014 Helsinki, Finland