1. Istituto Zooprofilattico Sperimentale delle Venezie Department of Chemistry Legnaro (PD) Italy
2. Istituto Zooprofilattico Sperimentale delle Venezie Microbial Ecology Unit Legnaro (PD) Italy
3. Present address: European Molecular Biology Laboratory Structural and Computational Biology Unit Heidelberg Germany
4. Istituto Zooprofilattico Sperimentale del Piemonte, Liguria e Valle d'Aosta CIBA Torino Italy