1. Manchester Institute of Biotechnology, School of Chemistry, Faculty of Science and Engineering, The University of Manchester, Manchester M1 7DN, UK
2. Biomolecular Analysis Core Facility, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, UK
3. Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA 92697-025, USA