The extreme conditions of life on the planet and exobiology

Abstract

Extreme physicochemical conditions (low and high temperatures, high salinity, low and high pH, high hydrostatic pressure, etc.) existing on Earth are compatible with the occurrence of microbial life. The diversity and metabolic features of microbial trophic groups inhabiting extreme environments (cold, hot, saline, acidic, alkaline, and deep marine) are described. They include hydrothermal vents, acid springs, hypersaline and/or alkaline lakes, permafrost, and deep-sea environments, etc. To live or survive under such drastic conditions, prokaryotes (Bacteria or Archaea) have developed a variety of physiological and metabolic strategies allowing them to adapt to in situ extreme conditions. Many of these extremophiles are recognized to be of industrial interest or to be potential candidates for future biotechnological applications. Clearly, the discovery of extremophiles living in terrestrial, subterrestrial, and deep marine environments has changed our perception of microbial life. One or a combination of extreme physicochemical conditions that they have to face may have prevailed in the primitive atmosphere and favored early extremophilic life not only on Earth but perhaps also on other planets.