Life in extreme environments: Approaches to study life-environment co-evolutionary strategies

The term extreme environments describes the conditions that deviate from what mesophilic cells can tolerate. These conditions are extreme in the eye of mankind, but they may be suitable or even essential living conditions for most microorganisms. Hyperthermophilic microorganisms form a branch at the root of the phylogenetic tree, indicating that early life originated from extreme environments similar to that of modern deep-sea hydrothermal vents, which are characterized by high-temperature and oxygen-limiting conditions. During the inevitable cooling and gradual oxidation process on Earth, microorganisms developed similar mechanisms of adaptation. By studying modern extremophiles, we may be able to decode the mysterious history of their genomic evolution and to reconstruct early life. Because life itself is a process of energy uptake to maintain a dissipative structure that is not in thermodynamic equilibrium, the energy metabolism of microorganisms determines the pathway of evolution, the structure of an ecosystem, and the physiology of cells. Following energy is an essential approach to understand the boundaries of life and to search for life beyond Earth.