Structural Characterization and Bioactivity of Exopolysaccharide Synthesized by Geobacillus sp. TS3-9 Isolated from Radioactive Radon Hot Spring

A thermophilic, endospore-forming, and radiation resistant bacterium, strain TS3-9, was isolated from the radon hot spring. Based on phenotype, fatty acid, G + C mol %, and phylogenetic analysis, TS3-9 was assigned to the genus Geobacillus. In addition to surviving exposure to gamol/La irradiation (D10 = 10 kGy), TS3-9 produced an exopolysaccharide (EPS), the average molecular weight was approximately 3.2 × 106Da. The results of partial acid hydrolysis, GC-MS, FT-IR, and NMR analysis showed EPS was a heteropolysaccharide, composed of D-mannose, D-glucose and rhamnose as its principal monosaccharide composition in the relative proportions, 1:0.14:0.06. The uronic acids and acetyl contents (wt. %) were at 18.6 % and 6.07 %, respectively. Evaluation of antioxidant properties indicated that the EPS had good activities in scavenging hydroxyl radical, superoxide radical, and DPPH. Preliminary in vitro tests revealed that the EPS could significantly restrain the proliferation of hepatoma carcinoma cell.