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Abstract
Haloalkalithermophiles are poly-extremophiles adapted to grow at high salt concentrations, alkaline pH values and temperatures greater than 50C. Halophilic alkalithermophiles are of interest from physiological perspectives as they combine unique adaptive mechanisms and cellular features that enable them to grow under extreme conditions. Water and sediment samples from the lakes of the Wadi An Natrun, Egypt and from Lake Magadi, Kenya were investigated for the presence of novel haloalkalithermophiles. These athalassohaline lakes are noted for their high temperature, alkaline pH and high Na+ concentrations. Two novel bacterial species, Natranaerobius jonesii and Natranaerobius grantii, and one novel archaeal species, Natronolimnobius aegyptiacus, were isolated and characterized. Furthermore, the adaptive mechanisms and bioenergetic properties of the species belonging to the order Natranaerobiales were investigated. Collectively, these microorganisms display a pH homeostasis, rather than an intracellular pH homeostasis; a growth requirement for Cl-; and are moderately UV resistant.