Life under Multiple Extreme Conditions: Diversity and Physiology of the Halophilic Alkalithermophiles

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Around the world, there are numerous alkaline, hypersaline environments that are heated either geothermally or through intense solar radiation. It was once thought that such harsh environments were inhospitable and incapable of supporting a variety of life. However, numerous culture-dependent and -independent studies revealed the presence of an extensive diversity of aerobic and anaerobic bacteria and archaea that survive and grow under these multiple harsh conditions. This diversity includes the halophilic alkalithermophiles, a novel group of polyextremophiles that require for growth and proliferation the multiple extremes of high salinity, alkaline pH, and elevated temperature. Life under these conditions undoubtedly involves the development of unique physiological characteristics, phenotypic properties, and adaptive mechanisms that enable control of membrane permeability, control of intracellular osmotic balance, and stability of the cell wall, intracellular proteins, and other cellular constituents. This minireview highlights the ecology and growth characteristics of the extremely halophilic alkalithermophiles that have been isolated thus far. Biochemical, metabolic, and physiological properties of the extremely halophilic alkalithermophiles are described, and their roles in resistance to the combined stressors of high salinity, alkaline pH, and high temperature are discussed. The isolation of halophilic alkalithermophiles broadens the physicochemical boundaries for life and extends the boundaries for the combinations of the maximum salinity, pH, and temperature that can support microbial growth.</jats:p>

Extraordinary solute‐stress tolerance contributes to the environmental tenacity of mycobacteria

“…30–35°C wide; Hallsworth and Magan, ; Kashangura et al ., ; Guinebretière et al ., ; Krenek et al ., ). Out of nine polyextremophilic bacteria and Archaea studied by Mesbah and Wiegel (), none had a temperature range, or demonstrated sustained growth above its temperature optimum, to a degree that equalled or exceeded the capabilities of the Mycobacterium species studied (Fig. A).…”

“…The mycobacteria tested were able to grow on benzene up to saturation (25 mM), and showed superior tolerance when compared with P. putida and A. wentii , on hexane and xylene (but not toluene; Table ). Whereas the majority of mycobacteria are not true extremophiles, their stress biology is nevertheless reminiscent of polyextremophiles, which are capable of tolerating multiple extremes (Mesbah and Wiegel, ). This said, the validity of the ‘polyextremophile’ concept has recently been brought into question (Alves et al ., ).…”

Adaptive strategies in the double-extremophilic prokaryotes inhabiting soda lakes

“…1.12) [10,59], the osmotic response in the vast majority of soda lake bacteria is based on the uptake and de novo synthesis of organic compatible solutes ( Fig. 1.13-14) (e.g.…”

The Role of Terrestrial Analogs in the Exploration of the Habitability of Martian Evaporitic Environments

“…The ability of microorganisms to adapt to the high concentration of certain ions is documented in different hypersaline lakes. At the alkaline lakes of the Wadi El Natrun (Egypt), for example, new anaerobic halophilic alkalithermophiles adapted to extremely high ion requirements (e.g., 1.4 M Cl − or greater) have been recently described Mesbah and Wiegel, 2012 ) .…”