Adaption to environmental stresses is vital for the survival of all organisms living in any environment. Two of the major environmental factors in the deep sea environment are high hydrostatic pressure and high salt concentration. Hydrostatic pressure and osmotic pressure share similarities in their effects on organisms living in the deep sea but this overlap has been little explored. Major studies from Japan and California over the last 40 years have shown the effects of hydrostatic pressure on bacteria from the deep sea (see [1] for a review). These are complemented by work by Yancey et al. [2] showing that specific solutes accumulated in response to osmotic pressure in fish have the ability to enhance resistance to hydrostatic pressure. However, this work has been done in vitro or with larger organisms and not much is known about the overlap of osmotic and hydrostatic pressure in bacteria. In this study I investigated the effects of osmotic and hydrostatic pressure on two model organisms: Photobacterium profundum and Escherichia coli. In order to accomplish this task I developed novel imaging equipment which allows for high resolution imaging of bacteria at pressure. I also developed a new method of growing bacteria in 96-well plates at high pressure, which lead to the identification of a hierarchy of genes essential for the growth of E. coli at pressure. I used the same 96-well plate technique to monitor the growth of P. profundum at differing osmotic and hydrostatic pressures. Furthermore I also attempted to analyse the solutes accumulated by different strains of P. profundum in response to osmotic and hydrostatic pressures.