What Are Extremophiles?

Sulfuric acid, boiling water, even the vacuum of space isn’t enough to kill these creatures. Extremophiles are organisms which live in the most extreme conditions. Some are simply tolerant of these conditions and can survive, but many of them thrive in them. Some live in places hotter than boiling water, while some prefer below 0 temperatures. There are multiple types of extremophiles, with most of them able to handle multiple extremes at once (polyextremophiles).

Boiling heat

Have you ever had boiling water splash on you? It hurts, doesn’t it? Well, there are some creatures that actually thrive in that temperature! They are called thermophiles.

One example includes the microbe Methanopyrus kandleri 116 strain grows at 122°C (252°F) – that’s 22°C (40°F) higher than the boiling point of water. No other life grows at temperatures this high. Another microbe, Pyrolobus fumarii, can grow at 113°C (235°F). Thermus thermophilus, the first thermophile discovered, grows between 50-80°C (122-180°F).

At these temperatures, most biomolecules break down. One significant molecule is DNA. Thermophiles survive by repairing their own DNA using a certain enzyme called reverse-DNA-gyrase. When the high temperatures rip apart DNA molecules, this enzyme takes those broken pieces and stitches them back together.

Freezing cold

Psychrophiles, on the other hand, prefer chilling out. In the natural world, -20°C (-4°F) is the lower limit for life. Bacteria have been seen thriving in sea ice and permafrost. One issue with such freezing cold is that ice crystals will form in the body’s fluids, tearing apart its tissues and cells. These creatures typically have a bio-antifreeze flowing through them to prevent this.

The red flat bark beetle (Cucujus clavipes) produces antifreeze proteins that prevent water molecules from gathering together. Larva have been seen surviving under imposed temperatures of -150°C (-238°F). They normally wouldn’t survive in these conditions unless they further altered their blood. They dehydrate themselves to concentrate the antifreeze. Their bodily water vitrifies instead of freezing, allowing water to stay in the body at sub-freezing temperatures without turning into ice and expanding.

Though these creatures have antifreeze in their blood, they still find hemoglobin valuable. The crocodile icefish doesn’t think much of it, and has opted to use as little as possible. So little, in fact, that its blood is clear. They are the only creatures (there are 16 species of them) that do not use hemoglobin to transport oxygen to their bodies. They live in temperatures around -2°C (28°F).

Highly acidic

Our stomach acid has a pH of 1. We know that there are strains of bacteria that live in our stomachs and are necessary for breaking down nutrients. Though these are considered acidophiles, other microbes can grow in pH levels as low as 0.06! The Picrophilus torridus lives in the most acidic environments known, and put our stomach bacteria to shame.

Most acidophiles do not survive with a naturally high bodily pH, but instead have highly advanced proton channeling systems that allow them to keep their bodies neutral (pH is dependent on protons, or hydrogen cations). Some acidophiles produce biofilms (groups of microorganisms) or fatty acids to prevent their cell membranes from falling apart.

Highly alkaline

Bleach has a pH ranging from 11-13. This is almost as basic as it gets. Some extremophiles, however, can live in pH levels of 12.5! The microbe Bacillus marmarensis strain DSM 21297 thrives in the most basic of environments. Another alkaliphile includes Spirochaeta americana. They live in the mud deposits of Mono Lake, reaching pH levels from 8-10.5. S. americana cannot live with oxygen and needs sulfur to survive.

Alkaliphiles survive in the opposite way acidophiles do: while acidophiles pump protons out of their cells, alkaliphiles pump them into their cells. They keep a bodily pH or about 8.

Under pressure

We’re used to thinking of methane as just a gas. Imagine such high pressures that methane forms into methane ice. Not only that, but imagine things actually living in it. Enter the methane ice worm! It lives on the sea floor of the Gulf of Mexico at pressures about 55 times that of the atmosphere at sea level. Imagine having 800 pounds per square inch (psi; about 5.5 megapascals, or MPa) of pressure on you. To the microbes living on the floor of the Mariana’s Trench, this is weak. They live in pressures of about 16,000 psi (110 MPa). The Pyrococcus yayanosii was shown to grow in pressures as high as 17,400 psi, or 120 MPa.

Barophiles, or piezophiles, protect themselves against the three main reasons why high pressure and life don’t typically get along: proteins and DNA get damaged, necessary chemical reactions do not occur at high pressures due to reduced volume, and cellular membranes become less fluid. These microbes will increase the concentration of fatty acids to keep their cell membranes fluid. They may also have enzymes that repair damaged DNA.


Radiation is harmful to humans because it damages our DNA. Some extremophiles can repair their DNA so quickly, that radiation doesn’t bother them so much. The Deinococcus radiodurans can survive radiation at levels 3000 times as high as that which would kill a human. Some radiation extremophiles even live in the Chernobyl site.

Salt, water, and chemicals

Halophiles are fans of salt. Haloferax volcanii lives in highly salty regions like the Dead Sea (which contains so much salt that people float on it). Brine shrimp and algae thrive in Mono Lake. Water flows in but not out, so all the minerals from the water collect in the mud when the water evaporates. This produces a highly mineral dense mud that most life would not survive in, let alone thrive. They survive by altering their proteins to resist salt.

Brine shrimp, though, use their gills and a special neck gland regulate their bodily salinity. They filter salt out of the water they breathe to maintain a salt balance. Their bodies themselves are impermeable to water, thus preventing water from being absorbed.

Giant tube worms thrive near hydrothermal vents. These are underwater vents powered by volcanic heat, releasing extremely hot water full of minerals and chemicals. While most organisms wouldn’t survive, microorganisms thrive to provide food for these giant tube worms. The worms are exposed to carbon dioxide and hydrogen sulfide. It metabolizes both of these, along with oxygen, to produce energy.

Xerophiles prefer environments with very little water. The Dunaliella algae lives in the driest place on Earth: Chile’s Atacama desert. They grow on spiderwebs and absorb the morning dew formed from air moisture.

Hyper-extremophiles: Tardigrades

Tardigrades are on a whole other level. They survive at higher and lower temperatures, pressures, and hydration levels than any other extremophile. They handle extreme levels of radiation, salinity changes, and chemical toxicity. They were even sent to space and not only lived, but reproduced. In space, they survived in a vacuum with no water nor oxygen while being exposed to X-ray and gamma radiation in near absolute zero temperatures. It makes you wonder how they die in the first place.

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