1. Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, Zürich, CH-8092 Zürich, Switzerland.
2. Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK.
3. Department of Biological Sciences, Imperial College of Science, Technology and Medicine, London SW7 2AY, UK.
4. M-SCAN Mass Spectrometry Research and Training Centre, Silwood Park, Ascot SL5 7PZ, UK.