Enzymes secreted by extremophiles are termed as extremozymes. Extremophiles are organisms that inhabit conditions which are extreme to survive and adapt in. Halothermothrix orenii is a polyextremophilic anaerobic bacterium that grows optimally at 60 C (maximum 70 C) in presence of 10 % NaCl (NaCl growth range between 4-20 %) and optimum pH 6.5-7.0, isolated from the sediments of Tunisian salt lake (Cayol et. al., 1994). This bacterium carry exclusive features from several points : (a) It is Gram-negative member of phylum Firmicutes and its genome analysis reveals mixed Gram-negative and Gram-positive properties such as lipid A biosynthesis, a characteristic of Gram-negative pathway and a typical Firmicutes sporulating system. (b) It is a strict anaerobic chemoorganotroph which uses various polysaccharides and produces a series of intracellular and extracellular glycosyl hydrolases and transferases. (c) It is a halothermophile and any extra-cellular enzymes produced by this organism are well adapted to function under thermophilic and saline conditions. (d) Halothermothrix orenii survives under fluctuating environmental conditions – dilution of salts during rains when temperature is low and increased salt concentration during summer when temperature is at its peak. In this study various glycosyl hydrolases and transferases from H. orenii selected for investigations are briefly described in chapter 3. Genes were cloned and over-expressed followed by protein purification were further analysed for their biochemical characteristics along-with structural insights.