has a mean temperature around 1 to 3 °C, and it is dominated by psychropiezophiles. In contrast, deep subsurface and hydrothermal vents in the seafloor are dominated by thermopiezophiles that prosper in temperatures above 45 °C (113 °F). Although the study of nutrient acquisition and metabolism within the piezosphere is still in its infancy, it is understood that most of the organic matter present are refractory complex polymers from the eutrophic zone. Both heterotrophic metabolism and autotrophic fixation are present within the piezosphere and additional research suggests significant metabolism of iron-bearing minerals and carbon monoxide. Additional research is required to fully understand and characterize piezosphere metabolism. Piezophilic adaptations High pressure has several effects on biological systems. The application of pressure results in equilibrium shifting towards state occupying small volume and it changes intermolecular distances and affects conformations. This also has an effect on the functionality of the cells. Piezophiles employ several mechanisms to adapt themselves to these high hydrostatic pressures. They regulate gene expression according to pressure and also adapt their biomolecules to differences in pressure. Nucleic acids High pressure stabilizes hydrogen bonds and stacking interactions of the DNA. Thus it favours the double stranded duplex structure of the DNA. However, to carry out several processes like DNA replication, transcription and translation, the transition to single-strand structure is necessary, which becomes difficult as high pressure increases the melting temperature, Tm. Thus, these processes may face difficulties. Cell membranes When pressure increases, the fluidity of the cell membrane is decreased as due to restrictions in volume they change their conformation and packing. This decreases the permeability of the cell membrane to water and different molecules. In response to flucatuation in environment, they change their membrane structures. Piezophilic bacteria do so by varying their acyl chain length, by accumulating unsaturated fatty acids, accumulating specific polar headgroups and branched fatty acids. Piezophilic archaea synthesize archaeol and cadarchaeol-based polar lipids, bipolar tetraether lipids, incorporate cyclopentane rings and increase in unsaturation. Proteins The macromolecules bearing the largest effect of pressure are proteins. Just like lipids, they change their conformation and packing to accommodate changes in pressure. This affects their multimeric conformation, stability and also the structure of their catalytic sites, which changes their functionality. In pressure-intolerant species, proteins tend to compact and unfold under high pressures as overall volume is reduced. Piezophilic proteins, however, tend to have less void space and smaller void spaces overall