Halophiles and Thermoacidophiles

Halophiles
Introduction:
Halophiles (Halo meaning “salt loving”) are bacteria that can live in extremely salty environments; some species can live in water with salt concentrations exceeding 15%. Most are photosynthetic autotrophs. The photosynthesizers in this category are purple because instead of using chlorophyll to photosynthesize, they use a similar pigment called bacteriorhodopsin, which uses all light except for purple light, making the cells appear purple or a pinkish color. They are mostly aerobic, have specialized cell walls, and carotenoids for ultraviolet protection.

How do they survive the high saline environments?:
Halophiles have to defeat the osmotic pressure, which drives the water out of the cell. This will kill the cell because water is essential to its survival. However they have developed a way to defeat this by producing or concentrating large amounts of a positively charged solute, called the “compatible solute.” Halophiles use this ability to balance out the osmotic pressure of the environment in order to protect themselves from the denaturing effects of salts. Usually halophiles will produce potassium ions because they have evolved in such a way that the enzymes they produce rely on them to function effectively. By producing these ions the osmotic pressure is relieved because the cell becomes more isotonic to its environment. Another way they reduce the osmotic pressure is by producing certain proteins designed to function in high ionic strength solution and maintaining high concentrations of inert solutes within their cytoplasm.
Structural difference:
Halophiles differ most dramatically in their construction of their lipid bilayer. Their fatty acly chains contain five carbon isoprenoid units, rather than the usual two. They also contain a pigment called bacteriorhodopsin, which they use to produce ATP. The cell walls contain no peptidoglycan, instead they have layers of glycoprotein to maintain their rod shape.
Examples:

Halobacterium is a genus of the Archaea that has a high tolerance for elevated levels of salinity. Some species of halobacteria have acidic proteins that resist the denaturing effects of salts. Halococcus is a specific genus of the family Halobacteriaceae.

Some hypersaline lakes are a habitat to numerous families of halophiles. For example, the Makgadikgadi Pans in Botswana form a vast, seasonal, high-salinity water body that manifests halophilic species within the diatom genus Nitzschia in the family Bacillariaceae, as well as species within the genus Lovenula in the family Diaptomidae. Owens Lake in California also contains a large population of the halophilic bacterium Halobacterium halobium.

Wallemia ichthyophaga is a basidiomycetous fungus, which requires at least 1.5 M sodium chloride for in vitro growth, and it thrives even in media saturated with salt. Obligate requirement for salt is an exception in fungi. Even species that can tolerate salt concentrations close to saturation (for example Hortaea werneckii) in almost all cases grow well in standard microbiological media without the addition of salt.

The fermentation of salty foods (such as soy sauce, Chinese fermented beans, salted cod, salted anchovies, sauerkraut, etc.) often involves halobacteria, as either essential ingredients or accidental contaminants. One example is Chromohalobacter beijerinckii, found in salted beans preserved in brine and in salted herring. Tetragenococcus halophilus is found in salted anchovies and soy sauce.

Thermoacidophile

Thermoacidophile is an extremophilic microorganism that is both thermophilic and acidophilic; i.e., it can grow under conditions of high temperature and low pH.The large majority of thermoacidophiles are archaea (particularly the crenarchaeota and euryarchaeota) or bacteria, though occasional eukaryotic examples have been reported. Thermoacidophiles can be found in hot springs and solfataric environments, within deep sea vents, or in other environments of geothermal activity.They also occur in polluted environments, such as in acid mine drainage.

An apparent tradeoff has been described between adaptation to high temperature and low pH; relatively few examples are known that are tolerant of the extremes of both environments (pH < 2, growth temperature > 80°C). Many thermoacidophilic archaea have aerobic or microaerophilic metabolism, although obligately anaerobic examples (e.g. the Acidilobales) have also been identified.

Sequencing the genome of a thermoacidophilic eukaryote, the red algae Galdieria sulphuraria, revealed that its environmental adaptations likely originated from horizontal gene transfer from thermoacidophilic archaea and bacteria.