Extremophiles - Extreme Organisms

Water Bear
This tiny aquatic invertebrate is called a Tardigrade or water bear. It is a highly resistant extremophilic animal, capable of inhabiting a vast range of altitudes, depths, salinities and temperature ranges, commonly found on mosses or lichens.

Photolibrary / Oxford Scientific / Getty Image

Extremophiles are organisms that live and thrive in habitats where life is impossible for most living organisms. The suffix (-phile) comes from the Greek philos meaning to love. Extremophiles have a "love for" or attraction to extreme environments. Extremophiles have the ability to withstand conditions such as high radiation, high or low pressure, high or low pH, lack of light, extreme heat, extreme cold, and extreme dryness.

There are different classes of extremophiles based on the type of extreme environment in which they thrive. Examples include:

  • Acidophile: an organism that thrives in acidic environments with pH levels of 3 and below.
  • Alkaliphile: an organism that thrives in alkaline environments with pH levels of 9 and above.
  • Barophile: an organism that lives in high-pressure environments, such as deep-sea habitats.
  • Halophile: an organism that lives in habitats with extremely high salt concentrations.
  • Hyperthermophile: an organism that thrives in environments with extremely high temperatures; between 80–122 °C or 176-252 °F.
  • Psychrophile: an organism that survives in extreme cold conditions and low temperatures; between −20 °C to +10 °C or −4 °F to 50 °C.
  • Radiophile: an organism that thrives in conditions with high levels of radiation, including ultraviolet and nuclear radiation.
  • Xerophile: an organism that lives in extreme dry conditions.

Most extremophiles are microbes that come from the world of bacteria, Archaea, protists, and fungi. Larger organisms such as worms, frogs, insects, crustaceans, and mosses also make there homes in extreme habitats.

Key Takeaways: Extremophiles

  • Extremophiles are animals that live and thrive under extreme environmental conditions.
  • Classes of extremophiles include acidophiles (acid lovers), halophiles (salt lovers), psychrophiles (extreme cold lovers), and radiophiles (radiation lovers).
  • Tardigrades or water bears can survive varied extreme conditions including excess dryness, lack of oxygen, extreme cold, low pressure, and toxins. They inhabit hot springs, Antarctic ice, seas, and tropical forests.
  • Sea monkeys (Artemia salina) are brine shrimp that thrive under extreme salt conditions and live in salt lakes, salt swamps, and seas.
  • H. pylori are spiral-shaped bacteria that live in the acidic environment of the stomach.
  • Cyanobacteria of the genus gloeocapsa can withstand the extreme conditions of space.

Tardigrades (Water Bears)

Water bears
Water bears (or tardigrades) are tiny invertebrates that live in coastal waters and freshwater habitats, as well as semi-aquatic terrestrial habitats like damp moss.

Power and Syred / Science Photo Library / Getty Images 

Tardigrades or water bears can tolerate several types of extreme conditions. They live in hot springs and Antarctic ice. They live in deep-sea environments, on mountain peaks, and even tropical forests. Tardigrades are commonly found in lichens and mosses. They feed on plant cells and tiny invertebrates such as nematodes and rotifers. Water bears reproduce sexually and some reproduce asexually via parthenogenesis.

Tardigrades can survive varied extreme conditions because they have the ability to temporarily suspend their metabolism when conditions are not fit for survival. This process is called cryptobiosis and allows tardigrades to enter a state that will allow them to survive conditions such as extreme desiccation, lack of oxygen, extreme cold, low pressure, and high levels of toxins or radiation. Tardigrades can remain in this state for several years and reverse their condition once the environment becomes suitable to sustain them again.

Artemia salina (Sea Monkey)

Sea Monkey
Artemia salina, also known as a sea monkey, is a halophile that lives in habitats with high salt concentrations.

De Agostini Picture Library / Getty Images

Artemia salina (sea monkey) is a brine shrimp that is capable of living in conditions with extremely high salt concentrations. These extremophiles make their homes in salt lakes, salt swamps, seas, and rocky coasts. They can survive in salt concentrations that are almost saturated. Their primary food source is green algae. Like all crustaceans, sea monkeys have an exoskeleton, antennae, compound eyes, segmented bodies, and gills. Their gills help them survive in salty environments by absorbing and excreting ions, as well as by producing a concentrated urine. Like water bears, sea monkeys reproduce sexually and asexually via parthenogenesis.

Helicobacter pylori Bacteria

Helicobacter pylori
These are multiple Helicobacter pylori which are Gram-negative, microaerophilic bacteria found in the stomach.

Science Picture Co / Subjects / Getty Images

Helicobacter pylori is a Gram-negative bacterium that lives in the extreme acidic environment of the stomach. These bacteria secrete the enzyme urease which neutralizes the hydrochloric acid produced in the stomach. Some bacterial species are a part of the stomach microbiota and can withstand the acidity of the stomach. These bacteria help protect against colonization by pathogens such as Helicobacter pylori. The spiral-shaped H. pylori bacteria burrow into the stomach wall and cause ulcers and even stomach cancer in humans. According to the Centers for Disease Control and Prevention (CDC), most of the world's population have the bacteria, but the germs don't cause illness in most of these individuals.

Gloeocapsa Cyanobacteria

Gloeocapsa Cyanobacteria
These are gloeocapsa (cyanobacteria) cells enclosed in layers of gelatinous material. They are photosynthetic, gram negative, nitrogen fixing, unicellular organisms that are able to survive the extreme conditions of space.

Ed Reschke / Photolibrary / Getty Images

Gloeocapsa is a genus of cyanobacteria that typically live on wet rocks found on rocky coasts. These cocci-shaped bacteria contain chlorophyll a and are capable of photosynthesis. Some also live in symbiotic relationships with fungi. Gloeocapsa cells are surrounded by gelatinous sheaths that may be brightly colored or colorless. Gloeocapsa species were found to be able to survive in space for a year and a half. Rock samples containing gloeocapsa were placed on the outside of the International Space Station. These microbes were able to survive extreme space conditions such as extreme temperature fluctuations, vacuum exposure, and radiation exposure.


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Bailey, Regina. "Extremophiles - Extreme Organisms." ThoughtCo, Sep. 7, 2021, thoughtco.com/extremophiles-extreme-organisms-373905. Bailey, Regina. (2021, September 7). Extremophiles - Extreme Organisms. Retrieved from https://www.thoughtco.com/extremophiles-extreme-organisms-373905 Bailey, Regina. "Extremophiles - Extreme Organisms." ThoughtCo. https://www.thoughtco.com/extremophiles-extreme-organisms-373905 (accessed June 5, 2023).