Adaptation to extreme environments: macromolecular dynamics in complex systems.

What we previously thought of as insurmountable physical and chemical barriers to life, we now see as yet another niche harbouring 'extremophiles'. Extremophiles and their macromolecules had to develop molecular mechanisms of adaptation to extreme physico-chemical conditions. Using neutron spectroscopy, we have demonstrated that molecular dynamics represents one of these molecular mechanisms of adaptation. To which extent do hyper-saline conditions and extreme temperatures influence molecular dynamics? First, molecular dynamics were analysed for halophilic malate dehydrogenase from Haloarcula marismortui (Hm MalDH) under different molar solvent salt concentration conditions influencing its stability. Secondly, mean macromolecular motions were measured in-vivo in psychrophile (Aquaspirillum arcticum), mesophile (Escherichia coli and Proteus mirabilis), thermophile (Thermus thermophilus), and hyperthermophile (Aquifex pyrofilus) bacteria. The mean constant force of Hm MalDH increases progessively with increasing stability. The results show that the molecular adaptation of Hm MalDH to hyper-saline conditions is achieved through an increasing resilience of its structure dominated by enthalpic mechanisms. The study of bacteria has provided tools to quantify the macromolecular adaptation to extreme temperatures in the naturally crowded environment of the cell. The macromolecular resilience of bacteria increases with adaptation to high temperatures.