1. Division of Molecular Microbiology, School of Life Sciences; University of Dundee; Dundee DD1 4HN UK
2. James Clerk Maxwell Building, School of Physics, and Astronomy; University of Edinburgh, The Kings Buildings, Peter Guthrie Tait Road; Edinburgh EH9 3FD UK
3. School of Life Sciences; University of Sussex; Falmer BN1 9QG UK