Diversity and Production of Extracellular Polysaccharide by Halophilic Microorganisms

Halophilic microorganisms derived from diverse thalassohaline and athalassohaline environments including marine estuaries, saline and soda lakes, inland solar salterns and acidic habitats are categorized as slight-, moderateand extreme halophiles according to their NaCl requirements. Taxonomic studies with culturable diversities of halophiles revealed that they belong to both Archaea and Bacteria representing the families Halobacteriaceae, Methanosarcinaceae and the class Gammaproteobacteria. As adaptive strategies against harsh salt stresses, majority of halophiles often synthesize and accumulate extracellular polysaccharides (EPS) which differ significantly in terms of their physical, chemical and material properties. So far the novelty in structure and functions of exopolysaccharides are concerned, producer strains belonging to the genera Halomonas and Haloferax have attracted the main attention. However, EPS producing strains belonging to the genera Idiomarina, Salipiger and Alteromonas are not uncommon. Through process optimization and metabolic regulation a number of potent halophilic strains have been found to produce copious amount of EPS indicating its commercial viability. Moreover, the significance of production, physicochemical and biological properties along with the possible applications of halophilic EPS in industry and biotechnology have also been highlighted.