In the 1970s, biophysicists took up the challenge of studying life under high stress after biologists isolated and characterised organisms that thrived in extremes of salinity, temperature, or pressure. The main methods and results of early experiments through to the latest discoveries regarding the molecular mechanisms of adaptation, as well as their significance in the search for extraterrestrial life, are reviewed here. The presence of liquid water is vital for life's processes, and a section on water describes its biologically relevant dynamic diffusion in extreme environments and inside microbial and human tissue cells. Research on halophilic proteins in solution permitted quantification of interactions with solvent involved in protein solubility, stability, and dynamics. Crystallographic studies on halophilic and hyperthermophilic proteins identified the features of adaptation to high salinity and temperature. The discovery of bacteriorhodopsin, a retinal-binding protein, in the membrane of an extreme halophile unlocked the structural study of membrane proteins in general. The study of a lactate dehydrogenase-like malate dehydrogenase in an extreme halophile opened up the exploration of evolutionary relationships and allostery in the malate/lactate dehydrogenase superfamily. The study of hyperthermophilic protease complexes provided important information on this functional group across domains. Adaptation via molecular dynamics measured in vivo by neutron spectroscopy in bacterial and archaeal cells is also discussed. In the conclusion, future research directions are outlined on microbial extremophiles in the deep sea and underground, in particular with respect to their global importance in climate change biology.
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