Extremophile

An extremophile (from Latin extremus meaning "extreme" and Greek philiā (φιλία) meaning "love") is an organism that thrives in physically or geochemically extreme conditions that are detrimental to most life on Earth.^]In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles.

In the 1980s and 1990s, biologists found that microbial life has an amazing flexibility for surviving in extreme environments—niches that are extraordinarily hot, or acidic, for example—that would be completely inhospitable to complex organisms. Some scientists even concluded that life may have begun on Earth in hydrothermal vents far under the ocean's surface.According to astrophysicist Dr. Steinn Sigurdsson, "There are viable bacterial spores that have been found that are 40 million years old on Earth—and we know they're very hardened to radiation." On 6 February 2013, scientists reported that bacteria were found living in the cold and dark in a lake buried a half-mile deep under the ice in Antarctica. On 17 March 2013, researchers reported data that suggested microbial life forms thrive in the Mariana Trench, the deepest spot on the Earth.Other researchers reported related studies that microbes thrive inside rocks up to 1900 feet below the sea floor under 8500 feet of ocean off the coast of the northwestern United States.According to one of the researchers, "You can find microbes everywhere—they're extremely adaptable to conditions, and survive wherever they are."

Classifications

Acidophile

An organism with optimal growth at pH levels of 3 or below

Alkaliphile

An organism with optimal growth at pH levels of 9 or above

Anaerobe

An organism that does not require oxygen for growth such as Spinoloricus cinzia. Two sub-types exist: facultative anaerobe and obligate anaerobe. A facultative anaerobe can tolerate anaerobic and aerobic conditions; however, an obligate anaerobe would die in the presence of even trace levels of oxygen

Cryptoendolith

An organism that lives in microscopic spaces within rocks, such as pores between aggregate grains; these may also be called Endolith, a term that also includes organisms populating fissures, aquifers, and faults filled with groundwater in the deep subsurface

Halophile

An organism requiring at least 0.2M concentrations of salt (NaCl) for growth^[11]

Hyperthermophile

An organism that can thrive at temperatures above 80 °C, such as those found in hydrothermal systems

Hypolith

An organism that lives underneath rocks in cold deserts

Lithoautotroph

An organism (usually bacteria) whose sole source of carbon is carbon dioxide and exergonic inorganic oxidation (chemolithotrophs) such as Nitrosomonas europaea; these organisms are capable of deriving energy from reduced mineral compounds like pyrites, and are active in geochemical cycling and the weathering of parent bedrock to form soil

Metallotolerant

Capable of tolerating high levels of dissolved heavy metals in solution, such as copper, cadmium, arsenic, and zinc; examples include Ferroplasma sp., Cupriavidus metallidurans and GFAJ-1^[12][13][14]

Oligotroph

An organism capable of growth in nutritionally limited environments

Osmophile

An organism capable of growth in environments with a high sugar concentration

Piezophile

(Also referred to as barophile). An organism that lives optimally at high pressures such as those deep in the ocean or underground;^[15] common in the deep terrestrial subsurface, as well as in oceanic trenches

Polyextremophile

A polyextremophile (faux Ancient Latin/Greek for 'affection for many extremes') is an organism that qualifies as an extremophile under more than one category

Psychrophile/Cryophile

An organism capable of survival, growth or reproduction at temperatures of -15 °C or lower for extended periods; common in cold soils, permafrost, polar ice, cold ocean water, and in or under alpine snowpack

Radioresistant

Organisms resistant to high levels of ionizing radiation, most commonly ultraviolet radiation, but also including organisms capable of resisting nuclear radiation

Thermophile

An organism that can thrive at temperatures between 45–122 °C

Thermoacidophile

Combination of thermophile and acidophile that prefer temperatures of 70–80 °C and pH between 2 and 3

Xerophile

An organism that can grow in extremely dry, desiccating conditions; this type is exemplified by the soil microbes of the Atacama Desert

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.