“
“Archaea that live at high salt concentrations are a phylogenetically

diverse group of microorganisms. They include the heterotrophic haloarchaea (class Halobacteria) and some methanogenic Archaea, and they inhabit both oxic and anoxic environments. In spite of their common hypersaline environment, halophilic archaea are surprisingly diverse in their nutritional demands, range of carbon sources degraded (including hydrocarbons and aromatic compounds) and metabolic pathways. The recent discovery of a new group of extremely halophilic Euryarchaeota, the yet uncultured Nanohaloarchaea, shows that the archaeal diversity and metabolic Protein Tyrosine Kinase inhibitor variability in hypersaline environments is higher than hitherto estimated. Life on Earth subsists over the whole range of salt concentrations encountered in natural and anthropogenic habitats. It thrives from freshwater environments to hypersaline lakes, solar salterns, and other salt-saturated environments. Hypersaline environments have a cosmopolitan distribution on our planet, and they are represented

selleck compound by aquatic systems, especially salt lakes, as well as saline soils (Rodriguez-Valera, 1988; Oren, 2002a, b; de la Haba et al., 2011). Microorganisms that live in this type of habitats are called halophiles (salt-loving organisms). The diversity in properties of saline and hypersaline habitats is reflected in the great variety of microorganisms adapted to live under these peculiar conditions. Extreme halophiles are generally defined as organisms that grow optimally in media with a concentration of 150–300 g L−1 (2.5–5.2 M)

NaCl, different from moderate halophiles that grow optimally in media with a concentration of 30–150 g L−1 (0.5–2.5 M) NaCl. Some nonhalophilic microorganisms are able to tolerate high salt concentrations and they are characterized as Sitaxentan halotolerant or extremely halotolerant organisms (Kushner & Kamekura, 1988; de la Haba et al., 2011). Halophilic and highly halotolerant species are found in each of the three domains of life: Archaea, Bacteria, and Eukarya. At the highest salt concentrations, halophilic members of the Archaea generally form the main component of the community, and therefore, they deserve a special interest. The Archaea (originally named Archaebacteria) were proposed as the third domain of life in the late 1970s (Woese & Fox, 1977; Woese et al., 1990). Based on phylogenetic analyses, several phyla/division were proposed within the domain: Crenarchaeota, Euryarchaeota, Nanoarchaeota, Korarchaeota, and Thaumarchaeota (Cavicchioli, 2011). The aim of this review is to briefly explore the diversity of the Archaea in hypersaline systems and to assess their metabolic contributions in these environments according to the recent findings in the field. Figure 1 presents a phylogenetic tree of the domain Archaea that includes representative taxa mentioned below. The class Halobacteria (Grant et al.