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Table 1 Classification of extremophiles and examples of their habitats.

From: Biotechnological applications of archaeal enzymes from extreme environments

Type Growth characteristics Habitat
Acidophiles Low pH (< 2) Hot sulfur springs, waste treatment plants, and mine drainage
Alkaliphiles High pH (> 10) Soda lakes, alkaline hot springs, deserts, and mine waste
Halophiles High concentration of salt (2–5 M NaCl) Salt lakes, coastal lagoons, and saline soils
Metallophiles High concentration of heavy metals (Cu, Cd, As, Zn) Deep-sea or terrestrial hydrothermal sources and metal-processing factories
Piezophiles or barophiles High hydrostatic pressure (40–130 MPa) Ocean floor and deep-sea hot vents
Psychrophiles Low temperature (< 15 °C) Arctic and Antarctic soils and waters, alpine soils, deep ocean water, and glaciers
Radiophiles High levels of ionizing radiation (> 25 kGy); 5 Gy is lethal for humans Terrestrial surfaces, upper layers of the sea, and nuclear waste
Thermophiles High temperature
    Thermophiles (60–80 °C)
    Hyperthermophiles (> 80 °C)
Deep-sea or shallow hydrothermal vents, hot springs, geysers, volcanoes, coal refuse piles, and industrial hot water systems
Xerophiles Low water activity (aw ≤ 0.8) Deserts and salt beds