The Biological Role of Water in Extreme Conditions

Despite exposure to extreme conditions, extremophilic organisms have developed a range of mechanisms to survive these detrimental perturbations to their solvent environment. In this thesis we study how extremes of pressure and salinity affect the aqueous environment with which extremophiles interact. To do this we employ a combination of neutron scattering with computational modelling to examine the perturbations to water structure, and nuclear magnetic resonance to examine the perturbations to water dynamics. We first examine perturbations to water structure and dynamics by simple monovalent model potassium halide salts and find that we can extract atom scale information which we can link to bulk measurable thermodynamic properties. We then use neutron diffraction to study the organic osmolyte TMAO in solution, which is used by high pressure adapted organisms to protect their biochemistry and find that it can preserve the structure of water against pressure induced perturbations. We then study aqueous magnesium perchlorate, a salt which is found in high concentrations in the Martian regolith, and likely in the surface lakes, and show that it induces a pressure-like effect on water structure. We then show that TMAO can also resist this pressure-like structural perturbation in the same way it can resist pressure induced structural perturbations. Finally, we investigate how magnesium perchlorate hinders biomolecular self-assembly by studying the amino acid glycine and the stability of the model protein I27. These fundamental insights help us to understand how observed adaptations in extremophilic organisms help them survive, with implications in medical and industrial settings.