Halophiles

Halophiles

The name "Halophiles" comes from the Greek word meaning salt-loving.

Halophiles live in ponds or salt lakes such as Great Salt Lake or Dead Sea.They thrive in highly salted environments inhibiting saline and hypersalinity.

There are extreme halophiles classified as mainly Archaea,  also bacterial halophiles and eukaryotic.

Examples of halophiles are Halobacterium salinarum,

Salinibacter ruber, Haloferux volcanii, Dunaliella salina.

Facultative halophiles survive and reproduce in high salty environment ( 2% salt) as well as in non - salted environments.

For example,  Staphylococcus aureus.

Obligate halophiles can survive only in high salt concentration (20% to 30 %) environments, such as, bacteria in Dead Sea, brine vats.

Halophiles use two different strategies for maintaining cell rigidity :

a) compatible strategy - most bacteria and eukarya.

b) Salt in strategy _ archaea.

Compatible  strategy

The compatible solutes strategy is used by most bacteria and eukarya to maintain turgor pressure. This method involves the continual synthesis of organic  solutes such as glycerol, sucrose and amino acids at a high energy expense.

These solutes balance osmotic pressure and allow the cell to function using normal enzymes and proteins at a high salinity.

Salt in strategy

Archaea of the halobacteriales use salt in strategy. This method uses active transport to pump selected external solutes for example,  potassium and chloride. The salt in strategy is much more efficient energetically,  but requires adaptation of enzymes and proteins to hypersaline environments.

Several species of halobacteriales produce an a exopolysaccharide (EPS) that forms an protective nutrient and ion absorbing mucous biofilm, that may help regulate transport of ions required for salt in strategy.

 Sulfated EPS also inhibits viral penetration into cells.

Halferux mediterranii and Haloarcula japonica both produce sulfated EPS.

Bacteriorhodopsin in Halophiles:

In extremely halophilic archaea, Halobacterium, a retinal protein called

bacteriorhodopsin is found. Bacteriorhodopsin acts as a transmembrane light - driven proton pump. It is composed of an opsin protein and a purple retinal, a molecule that absorbs photons.

When photon of the light energy hits bacteriorhodopsin, the retinal isomerizes from all - trans to 13 - cis and protons across cell membrane. Bacteriorhodopsin creates a proton gradient that can be used by an F - class ATPase to synthesize ATP in anaerobic environment.

Halophiles Written By

Sadia Akhtar
Student of Department of Microbiology
Jagannath University.
Email- sadiabd810@yahoo.com