Survival of bacteria in the natural environment is dependent on the ability of the cell to adapt to extremes of pH, temperature and osmotic stress. Mechanosensitive channels are large non-selective channels found in the cytoplasmic membrane of.bacterial cells that are required for the survival of hypoosmotic shock. E. coli cells lacking both MscL and MscS are unable to survive hypoosmotic shock (Levina et a/., 1999), however they exhibit functional redundancy in that reintroduction of either of these two channels is sufficient to restore survival. The overall objective o(this study was to examine the structure and function ofMscS, the mechanosensitive channel of small conductance in E. coli. A crystal structure for MscS was published by Bass and co-workers in 2002, which has driven much of the research into the gating mechanism of this channel. The work presented in this thesis aimed to address the structural requirements for maintenance of a sealed channel pore under normal physiological conditions and the conformational changes that occur during gating. This study has demonstrated two residues, Leul05 and Leu109, to be critical in the formation of a hydrophobic seal at the base of the pore. Further mutational . analysis has demonstrated that conserved Gly and Ala residues, which form the packing interface of the pore-lining helices, are crucial for the gating transition. In addition to the structural analysis of MscS, the relationship between mechanosensitive channels and membrane active food preservative compounds was investigated as previous studies had demonstrated that cells lacking mechanosensitive channels were more resistant to paraben food preservatives. Finally, to assay the function of MscS and MscS mutants, a fluorescence-based method for determination of cell viability following hypoosmotic shock was developed.