Physicochemical boundaries of life

Abstract

Extremophilic organisms are found in all three domains of life - Bacteria, Archaea, and Eukarya. They tolerate or even require habitats which are characterized by extreme factors, such as low water activity, scarce nutrients and extremes of temperature, pH, pressure and toxic compounds. Most extremophiles are prokaryotes, with Archaea accounting for the largest proportion, but the group also includes Eukarya such as algae, fungi and protozoa, and even multicellular organisms. This chapter provides an overview of the extreme environmental factors which influence life on Earth, a short survey of the various types of extremophiles - including viruses - as well as an update of current records for the limits of growth by extreme environmental factors and survival of extreme conditions. The interest in extremophilic microorganisms is growing, particularly since they survive exposure to space conditions and may possibly be capable to live in extraterrestrial environments.