Top 11: Extremophiles

Extremophiles can live just about anywhere. That’s great, however what the hell are extremophiles?

That’s is what you are thinking, right?


Well, the name, that literally means extreme loving, as proposed in 1974 by the scientist R.D. MacElroy to designate any organism able to support environmental conditions usually fatal to most eukaryotic cells, and the term extremophile is relatively anthropocentric.

Usually, we tend to judge habitats based on what would be considered “extreme” for human existence; many of them couldn’t survive in supposedly normal, moderate environments. For example, the microorganism Ferroplasma aci­diphilum ­needs a large amount of iron to survive, quantities that would kill most of other life forms. Other organisms, for example, consider oxygen to be poisonous. While oxygen is a necessity for life as we know it, some organisms flourish in anoxic environments.

The extremophiles listed below are grouped on the basis of the main characteristics of their environment.

1. Thermophiles

Thermophiles are adapted to temperatures generally exceeding 60ºC. Some extreme thermophiles (hyperthermophiles) require a very high temperature (80°C to 105°C) for growth.

An extraordinary hyperthermophile is a recently discovered Strain 121, found in a water sample from a ‘black smoker’ hydrothermal vent called Finn in the northeast Pacific Ocean, about 320 km off Puget Sound, in the U.S. state of Washington. Tests in laboratory showed that not only did it survive high pressure autoclave sterilization at 121ºC, but its cell numbers also doubled over 24 hours at that temperature.

The record temperature for survival and reproduction is 122°C by Methanopyrus kandleri, found on the wall of a hydrothermal vent in the Gulf of California, at a depth of 2000 m, at temperatures of 84–110 °C.

2. Psychrophiles

Psychrophiles can readily grow and reproduce in cold temperatures, ranging from −20°C to +10ºC.

The microbe Psychrobacter arcticus in on the cold front, and it has been isolated from sea-ice and Antarctic glaciers. Permafrost soils are extreme environments that exert low-temperature, desiccation, and starvation stress on bacteria over thousands to millions of years.

One strain, 273-4, was found in a Siberian permafrost core more than 20,000 years old. According to Cornell University’s Peter Bergholz, one of the team investigating the find, the bugs were not hibernating but growing and dividing, albeit very slowly.

3. Halophiles

Halophiles (from the Greek, salt-loving) live in high salt concentrations, exceeding the salinity of seawater by more than a factor of 10.

The first description of a unicellular biflagellate red-colored algae living in concentrated brines was given in 1838 by Dunal, who reported occurrence of the organism we know today as Dunaliella salina in the salterns of Montpellier, on the Mediterranean coast of France.

4. Alkaliphiles

Alkaliphiles can easily thrive in alkaline (pH roughly 8.5-11) environments, growing optimally around a pH of 10.

The tiny archaea of the genus Natronobacterium was first identified in samples taken from Lake Magadi, Kenya. This extremophile creature live in waters extremely rich on sodium carbonate. For most of the year the lake has an 80% covering of soda.

5. Acidophiles

Acidophiles are those that thrive under highly acidic conditions (usually at pH 2.0 or below).

Cyanidium caldarium is an algae that can be found in acidic hot streams, bogs, and moist acidic soils all over the world. This algae use photosynthesis to acquire their nutrients and it can withstand liquids with pH values of around 2 (indicative of extreme acidity) and is found in waters near geysers in Yellowstone National Park in the US and other volcanic regions.


6. Metallophiles

Metallophiles can survive in high concentrations of heavy metals.

The microbe Ferroplasma acidarmanus is an aquatic archaeon found in streams draining iron mines, most notably Iron Mountain in California. This amazing microbe has the ability to convert sulfide found in metal ores to highly concentrated sulfuric acid.

The conditions in these streams are extremely harsh due to high levels of sulfate created as a result of mircobial metabolism, leading to a pH between 0 and 2.5. This amazing microbe is one of the few that can survive at such a low pH and can be seen in the stream as streamers of biofilm.

7. Piezophiles

Piezophiles or barophiles can be successful in environments exposed to hydrostatic pressures as high as about 1000 atmospheres.

Some Tardigrades (Tardigrada), also known as water bears or moss piglets, are a phylum of small invertebrates, and they can withstand extremely low pressures, with one species surviving the vacuum of space for 10 days. Others can live in bottom of the Mariana Trench withstanding excessively high pressure of 1000 atmospheres. In laboratory some survived the amazing pressure of 6000 atmospheres.

8. Radioresistant

Radioresistance is the property of organisms that are capable of living in environments with very high levels of ionizing radiation.

Discovered in 2003 in a seafloor hydrothermal vent off the coast of California, the Thermococcus gammatolerans is an archaea hyperthermophile and is the most radiation resistant organism known to science. It can withstand 30,000 Grays of radiation (a Gray is the absorption of one joule of such energy by 1 kg of matter). Five Grays is enough to kill a human.

9. Xerophile

Xerophiles live in extreme dry environments. They are able to survive in environments with water activity below 0.8.

Examples of xenophiles are Trichosporonoides nigrescens, Cacti, and Tardigrades, they can survive for almost a decade without the exposure to water.

Cacti show many adaptations to conserve water. Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. Most Cacti live in extremely dry environments, even being found in the Atacama Desert, one of the driest places on earth.

10. Anaerobe

Many extremophiles are anaerobic organisms. Unlike us, anaerobes do not require oxygen to live. Anaerobes can either be facultative anaerobes or obligate anaerobes. Facultative anaerobe can tolerate anaerobic and aerobic condition; however, an obligate anaerobe would die in presence of even trace levels of oxygen.

The first animals that do not depend on oxygen to breathe and reproduce have been discovered by scientists on the bed of the Mediterranean Sea. Three species of creature, which are only a millimeter long and resemble jellyfish encased in shells, were found 3.5 km underwater on the ocean floor, 200 km off the western coast of Crete, in an area entirely depleted of oxygen, or anoxic. One of the three Loriciferans (so-called because of their protective layer, or lorica) has been named Spinoloricus Cinzia.

11. Polyextremophile

A polyextremophile is an organism that fits into more than one extremophile category; most extremophiles fit under this classification.

The bacterium Deinococcus radiodurans shows remarkable resistance to a range of damage caused by ionizing radiation, desiccation, UV radiation, oxidizing agents, and electrophilic mutagens, and is therefore known as a polyextremophile, entering The Guinness Book Of World Records as the world’s toughest bacterium.

Discovered in 1956 in a can of ground meat that had been treated with large doses of radiation to remove all hazardous bacteria from the product, they thought the dose of radiation would kill all known forms of life, but the meat subsequently spoiled and D. radiodurans was found to be the culprit. It can also survive a vacuum, dehydration, intense cold and acid.


Extremophiles are a cornerstone in the theory of panspermia who claims that life exists throughout the Universe, distributed by meteoroids, comets, asteroids and planetoids.

We call them extremophiles… but that is one sided perspective. If they could think, what would they think of us?I tell you what they might think: poor humans, so defenseless.

I mean, if the world becomes a inhospitable place, the human race is really in trouble. I am afraid to say it guys, but the truth is that, we will not stand a chance against the little suckers that are the extremophiles.