Extremophiles: An Overview

Earth contains several environmental extremes which are uninhabitable for most of the living beings. But, astonishingly, in the last few decades, several organisms thriving in such extreme environments have been discovered. “Extremophiles”, meaning “Lovers of Extremities” are the entities that are especially adapted to live in such harsh environmental conditions in which other entities cannot live. The discovery of extremophiles has not only boosted the biotech industry to search for new products from them, but also made researchers to think for the existence of extra-terrestrial life. The most inhospitable environments include physical or chemical extremities, like high or low temperatures, radiation, high pressure, water scarcity, high salinity, pH extremes, and limitation of oxygen. Microorganisms have been found to live in all such environmental conditions, like hyperthermophiles and psychrophiles, acidophiles and alkaliphiles. Bacteria like Deinococcus radiodurans, which is able to withstand extreme gamma radiation, and Moritella sp., able to grow at atmospheric pressure of >1000 atm, have been reported. Environments like the Dead Sea, having saturated NaCl concentrations, hold extreme halophiles like Halobacterium salinarum. Highly acidic environments, like the Rio-Tinto River in Spain or Danakil depression in Ethiopia harbour acidophiles with growth optima of pH zero, or close to it. Bacillus alcalophilus, and Microcystis aeruginosa on the other hand inhabit natural alkaline soda lakes where pH can reach about 12.0. A number of anaerobic prokaryotes can live in complete anoxic environments by using terminal electron acceptors other than oxygen. In this chapter, we shall discuss very briefly the diversity of all extremophiles and their mechanism(s) of adaptation.