An extremophile is an organism that thrives in extremely hot, cold, acidic, basic, salty, or other conditions that are considered inhospitable to most life on Earth. Many extremophiles live in environments where few other organisms can survive because they have adapted special features that enable them to endure these conditions. For example, some extremophiles can withstand high doses of ionizing radiation and others can live without oxygen.
Extremophiles are found in all three domains of life: archaea, bacteria, and eukarya. The term “extremophile” was first coined by microbiologist Thomas D. Brock in 1977 to describe bacteria he found living at temperatures above 80°C (176°F) in hot springs. Since then, many different types of extremophiles have been discovered living in a wide range of extreme environments. Extremophiles are important for several reasons: they help us understand the limits of life on Earth and how life might adapt to new environments; they play key roles in global biogeochemical cycles; and their unique properties may offer potential for biotechnological applications.
Extremophiles occur naturally on every continent and island on Earth. They can be found near hydrothermal vents deep under the ocean; within glaciers; inside rocks miles below the surface; around geysers and hot springs; near nuclear reactors; and even floating in clouds high above the ground. No matter where they live, all extremophiles share one common trait: they have evolved ways to survive under conditions that would be lethal to most other organisms.
One well-known type of extremophile is the thermophile—an organism that thrives at high temperatures (above 50°C or 122°F). Thermophilic microbes are often found near hydrothermal vents or hot springs where water temperatures can exceed 100°C (212°F). One particularly interesting group of thermophilic microbes are the “haloarchaea” which live in hypersaline lakes such as those found in Death Valley National Park (USA), Great Salt Lake (USA), Lake Retba (Senegal), Salar de Uyuni (Bolivia), among others. Haloarchaea are able to tolerate salt concentrations up to 30%—several times higher than what is typically found in seawater (~3%).
Another type of extremophile is the psychrophile—an organism that grows best at low temperatures (<20°C or 68°F). Psychrophilic microbes are commonly foundin polar regions such as Antarctica and Greenland where air temperatures can dip below -40°C (-40°F) during winter months. Some psychrophilic microbes also inhabit permanently cold environments such as permafrost soilsand glaciers. Notable examples include members of the bacterial genera Pseudomonasand Shewanella which can metabolically generate heat via cellular respirationto melt ice surrounding them when nutrients become scarce.. Other well-known groups of extremophiles include halophytes(organisms that growin saltwater), acidophiles(organisms that thriveat low pH values), alkaliphiles(organisms tolerantof high pH values), xerophytes(desert plants adaptedto withstand long periodsof drought), piezophiles(deep-sea organismsadaptedto high pressures), barotolerantmicrobes(organisms capableof withstandinghigh hydrostaticpressures)