الفهرس 
Characteristics of hypersaline environmentsOnly 14 pages are availabe for public view
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Abstract
The groups of extremely salt-loving halophilic microbes that produce red, pink, and purple hues in hypersaline ponds were among the earliest microorganisms to be recognized and described. The word halophile is derived from two Greek words, ”halos” and ”philus,” meaning, ”salt” and ”loving” respectively (Leichtw, 1978).
Halophilic bacteria can grow in very high salt concentrations without denaturation of its proteins, giving them some biotechnological importance (Eisenberg & Wachtel, 1987; Danson, 1988). The proteins themselves appear halophilic in that they are only stable in solvents of very high salt concentration (Danson, 1988).The order Halobacteriales consists of a large group of aerobic microbes that live and grow in hypersaline (i.e. brine) environments such as the Great Salt Lake and the Dead Sea. Members of this order are the most halophilic organisms known to exist, thriving in environments 10 times saltier than seawater; hence, collectively they are referred to as the ‘extreme halophiles’ (Grant et al., 2001).However, the extreme halophiles are well adapted to their hypersaline environment, as evidenced by their predominance in these habitats, requiring at least 1.5 M NaCl for growth and 3.5- 4.5 M NaCl for optimal growth (Grant et al., 2001). To prevent dehydration and maintain osmotic balance with their surroundings, the extreme halophiles have a high intracellular concentration of salts, as high as the NaCl concentration in their environment. They counterbalance high extracellular salt concentrations by accumulating KCl within the cell up to concentrations close to saturation (Chin et al., 2010; Golyshina, 2011; Cray et al., 2013b; Harrison et al., 2013; Krisko & Radman, 2013; Oren, 1999; Roberts, 2005)Their enzymes have evolved particular features that confer to them stability and solubility in high salt concentrations. Furthermore, chloride and sodium ions are involved in salt bridges that lock subunits together (Pace, 1997; Yakimov et al., 2014).High numbers of taxonomically diverse extremely halophilic microorganisms were identified, that differ in salt requirements and metabolic capabilities (Oren, 1994, 2002; Grant et al., 1998, 2001; Anton et al., 2000; Madigan et al., 2003). Among these halophilic microorganisms, Archaea are the most common (Anton et al., 2000; Oren, 2002). In extremely halophilic microorganisms, the distinction of halophilic Archaea from halophilic bacteria became apparent in the 1970’s through the molecular phylogenetic work of Woese, who proposed the three domain view of life (Grant & Larsen, 1990). While halophilic microorganisms represented many different taxonomic groups in the bacterial domain, those in the archaeal domain fell into a single order (Halobacteriales) and family Halobacteriacae (Grant & Larsen, 1990).These extreme halophiles grow best at high salinites (3.4- 5 M NaCl) but they tolerate only 2 M magnesium (Bolhuis et al., 2004). They form dense blooms (upto 108 cells ml-1) and resulting in the red colour of many brines.
Common species of halobacteria are rods, cocci or disc-shaped, flat discs (Halococcus), squares (Haloferax), rectangles (Halobacterium) and triangles (Haloarcula) (Grant et al., 2001). Although triangular and even squar cells with sharp corners measure 2- 5 μm wide, but less than 0.2 μm thick.They are either Gram- negative or Gram- positive, and many are pleomorphic (Anton et al., 1999; Oren et al., 1999; Oren, 2002; Walsby, 2005).
The current study was conducted in order to isolate halophilic bacteria from both red sea and mediterranean sea coasts. the obtained isolates (57 in total) were identified, according to their phenotypic and genotypic characteristics, as belonging to three groups