Physio-chemical and biological properties of partially purified exopolymers from newly isolated halophilic bacterial strain SM5

An extremely halophilic bacterial strain SM5 producing exopolymers was isolated from Thai traditional fermented fish (Pla-ra). Morphological and biochemical properties and 16S rDNA sequencing revealed that the strain was Halobacterium sp. SM5. The exopolymers were identified as a water-soluble acidic polymer. They contained 70.40±0.70% (w/w) protein as a major component and 7.30±0.01% (w/w) sulfate as a minor component, as well as 5.02±0.30% (w/w) total sugar, 3.15±0.10% (w/w) neutral sugar and 2.05±0.10% (w/w) uronic acid. Fourier transform infrared (FT-IR) analysis showed that the exopolymers consisted of carboxyl, hydroxyl, amino and sugar derivative groups. Molecular weight of the exopolymers was 7.7x104 and 2.5x105 Da. Cytotoxicity effect of the exopolymers on the HT29 human cell lines revealed that the exopolymers concentration of 0.1 and 0.5 mg/ml gave the cell a viability of 93.48 and 98.46%, respectively. At the exopolymers concentration of 1.0, 1.5 and 3.0 mg/ml, the cell viability was 71.65, 74.28 and 57.77%, respectively. The exopolymers showed pseudoplastic property, resistance to shearing, and high viscosity (600 cP). Viscosity was increased with the exopolymers concentration (0.5-4.0% w/v). The exopolymers were stable over a wide pH range (6-8), and their viscosity decreased at temperatures above 60oC