\Chapterstar{Declaration}
The work in this thesis was undertaken at the University of Oxford; in the Microbiology Unit, Department of Biochemistry and in the Clarendon Laboratory, Department of Physics.  Work was performed from October 2005 to October 2008 under the supervision of Prof. J.P. Armitage.  All the work in this thesis is my own unless stated and has not been submitted for a degree at this or any other university.