ABSTRACT
The discovery of microbial life in seemingly prohibitive environments continues to challenge conventional concepts of the growth-limiting conditions of cellular organisms. In the last few decades, it has become clear that microbial communities can be found in the most diverse conditions, including extremes of temperature, pressure, salinity, and pH. The diversity of extremophiles has barely been tapped, and estimates generally agree that <1% of the microorganisms in the environment have been cultivated in pure cultures to date. Many parts of the world are defined as extreme, such as geothermal environments, polar regions, acid and alkaline springs, and the cold, pressurized depths of the ocean. As conditions become more demanding, the microbial population is constituted exclusively of microorganisms belonging to the bacterial and archaeal domain.
