Abstract

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 7.7×10 ⁴ and 2.5×10⁵ 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 60°C.