Microorganisms in extreme pressure (Piezophiles/ Barophiles)

Piezophile Definition and Characteristics

• Barophiles are defined as organisms that grow and thrive optimally at pressures greater than atmospheric pressure.
• The term piezophile is used as a replacement to barophile as piezo means pressure in Greek.
• Barophilic bacteria have been isolated from various deep-sea environments throughout the world and have been grown rapidly at low temperatures and high pressures.
• Bacteria living in the deep-sea display several unusual features that allow them to thrive in their extreme environment.
• Most barophilic organisms tend to be psychrophilic and thus cannot be cultured at a temperature above 20°C.
• Similarly, many barophiles tend to be obligate barophiles with few archaea acting as moderately barophilic.
• It has been seen that the pressure needed for the maximal rate of reproduction at 2°C may reflect the true habitat depth of an isolate.
• High pressure affects the survival of microorganisms, where it influences the membrane structure and functioning of the cell.
• High pressure and low temperature in deep-sea environments decrease the fluidity of lipids and even depress the functions of biological membranes.

Piezophile Mode of adaptation

Membrane

• High pressure might cause the formation of a gel-like membrane which then decreases nutrient uptake and processing.
• Barophiles produce increased levels of unsaturated fatty acids in the lipids and increasing the extent of fatty acid unsaturation can maintain the membrane in a functional liquid crystalline state at high pressures, low temperatures, or both.
• The reduced fluidity gives a defined structure to the membrane, which supports the normal functioning of the cell.

Proteins

• The high-pressure condition suitable for barophiles results in conformational changes in the proteins that inhibit their function.
• In order to prevent such changes, barophilic proteins usually have lower concentrations of proline residues and a higher concentration of glycine residues.
• The proline residues have cyclic side chains that disrupt alpha-helices, whereas the glycine residues have small side chains with high conformational flexibility.
• The increased flexibility prevents the disruption of alpha helices and protects the function of such proteins.

Piezophile Examples

• Some common examples of barophilic microorganisms are Shewanella benthica, Moritella yayanosii, Shewanella violacea, Photobacterium profundum, Moritella japonica, Sporosarcina spp, etc.