1. Microbial Physiology Research Group, Division of Biosphere Sciences, University of London, Kensington Campus, Campden Hill Road, London W8 7AH, U.K.
2. Metals in Biology and Medicine Centre, Division of Biomolecular Sciences, King's College, University of London, Kensington Campus, Campden Hill Road, London W8 7AH, U.K.