Life under extreme conditions

What are extremophiles?

Extremophiles are microorganisms that can live in environments, which are considered by humans to be extreme. These microorganisms, mostly prokaryotes belonging to the domains Bacteria and Archaea, are adaptedto survive in ecological niches such as at high or low temperatures (160-230°F or 70-110°C; 32-50°F or 0-10°C), extremes of pH (acidic or alkaline conditions; pH below 4 and above 9), high salt concentrations (above 20% salt), and high pressure (above 300 atmospheres). Extensive work since the mid-1980s has clearly demonstrated that extremophiles are interesting objects for basic research and innovative biotechnology.

Where do they live?

Biotopes of extremophiles: The extremophiles include several groups: thermophiles, psychrophiles, alkaliphiles, acidophiles, barophiles and halophiles. Thermophiles and psychrophiles. The most common biotopes (environments) in which thermophiles (heat lovers) grow optimally are of geothermal origin, and are usually associated with tectonically active zones. Terrestrial biotopes are mainly solfataric (relating to a volcanic area) fields, which consist of soils, mud holes, and surface waters heated by volcanic exhaust from magma chambers below. The surface of solfataras is rich in sulfate and is very acidic (pH 0.5-4.0). Marine hydrothermal systems are situated in shallow and abyssal depths, and consist of hot fumaroles, springs, and deep-sea-vents (“black smokers”) with temperatures up to 750°F or 400°C. Due to the presence of reducing gases, most biotopes of thermophiles do not contain oxygen and are anaerobic. However, the surface of the terrestrial solfataric fields contains high amounts of oxygen and therefore harbors aerobic microorganisms.

Additional communities of thermophiles have been discovered in artificial high-temperature biotopes, such as smoldering coal refuse piles and geothermal power plants. They also have been isolated from oil-bearing, deep, geothermally heated soils. Most psychrophilic (cold-loving) microorganisms thrive in Polar Regions, especially in Antarctic seawater and deep-sea sediments, which represent permanently cold habitats ranging from 28 to 39°F (-2 to 4°C). Alkaliphiles and halophiles. Alkaline ground water, soda lakes, and deserts harbor microorganisms that are able to grow at pH values above 9 (alkaliphiles) and at high salt concentrations (halophiles). Halophilic microorganisms colonize saline environments, where the salinity may range from that of sea water (3%) to that of saturated solutions (35%, as in dead-sea, hypersaline lakes and in saline soils). Halophilic microbes can also be isolated from artificial environments such as salted food.

Acidophiles and barophiles. Extremely acidophilic microorganisms are usually found in terrestrial and marine solfataric fields. Many microbial communities in these environments are adapted to grow at low pH values (about 1.0-3,5) and high temperatures (158-185°F or 70-85°C) and are designated thermoacidophiles. Microorganisms that are able to survive only at high pressure in the deep sea are known as strict barophiles. Such microbes have been discovered in deep-sea sediments collected from depths of 9800-32,800 ft (3000-10,000 m).