Microbial Diversity, Life Strategies, and Adaptation to Life in Extreme Soils

Abstract

There is no general consensus on how to define an extreme environment. From an anthropocentric point of view, physicochemical conditions supporting mammalian life appear as normal, and conditions deviating from these are considered as extreme. However, what is extreme and what is normal for microbes remains debatable, and the concept “extreme†as we use it may not necessarily be appropriate for micro-organisms (Gorbushina and Krumbein 1999). Micro-organisms dwell in virtually all types of soil habitats. These range from extremely dry and cold deserts in the Antarctic and deep into permafrost soils to geothermal and humid soils in volcanic areas, from extremely acid mines with sulfuric acid to high alkaline areas. Microbial life can also exist in salt crystals, under extremely low water activity, and low nutrient concentrations. As a group, micro-organisms have the highest ability of all life forms to adapt to extreme and stressful environments. This includes new types of habitats created by anthropogenic activities, such as those polluted with heavy metals, radionuclides, and high concentrations of toxic xenobiotic compounds (e.g., polychlorinated biphenyls, hydrocarbons, and pesticides).