True to their name (which is a Greco-Latin combo for "someone who loves extremes"), extremophiles can batten and fatten in conditions that humans – and most other species – would consider off limits. The first of these sturdy organisms to be discovered, a thermophile, was found in the late 1960s in Yellowstone National Park, hanging out in one of the hot springs. It was a bacterium with a name bigger than itself: Thermus aquaticus (literally, "warm bath water dweller." Species names are often surprisingly prosaic once you translate them.)

Thermus aquaticus not only withstood, but thrived, in temperatures above 160 F. For comparison, try turning on the hot water tap at home, and let it run. It will scald your hand, but the temperature won’t exceed 140 F. This is observational proof that you are not a thermophile.

As it turns out, Thermus aquaticus is only middle-of-the-road tough when it comes to taking the heat. One hyperthermophile, Pyrolobus fumarii, can tread water at a scalding 235 F. That’s not only above the boiling point, but it will soften the upholstery in your pickup. Other extremophiles operate smoothly in below-freezing cold (psychrophiles), highly acid or base solutions (acidophiles and alkaliphiles), heavy-duty brines (halophiles), and in circumstances of crushing high pressure or dusty dryness (piezophiles and xerophiles). There are varieties that can shrug off nuclear radiation, or dwell well in aviation fuel. Frankly, extremophiles would be recruited for the local SWAT team, if they were big enough to carry weapons.

How do they do it? What defenses do these frequently diminutive creatures (many are microbial, although not all - think penguins) mount against environmental conditions that would either pickle or pyrolize you and me? There are two fundamental strategies: erect a barrier against the elements, or change your metabolism.

For example, some halophiles protect themselves from a saline environment by increasing the concentration of salts in their innards. With salinity about the same both within and without the cell, the halophile needn’t fear that runaway osmosis will drain it of its precious water.

If you can’t defend against a brutal habitat, you can learn to love it. For example, psychrophiles come equipped with special proteins to adapt their lifestyle to the cold. Some of these proteins act as antifreeze to lower the freezing point of water, to prevent its congealing, expanding, and sundering the cell. Other proteins (enzymes) are specially formulated to ensure that chemistry continues even when the temperature dips to the single digits or lower.

Many researchers are looking for ways to exploit the Darwinian inventiveness that has produced these extremophile defense mechanisms. For example, Deinococcus radiodurans, which boasts a highly sophisticated DNA repair shop within its tiny cell walls, is able to recover from exposure to massive doses of molecule-busting, high energy radiation by simply fixing the damage. It’s hoped that this talent will prove useful in engineering microbes that can clean up radioactive spills, or possibly even protect us from skin cancer.

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