Production and Structural/Physicochemical Characteristics of Exopolysaccharides from the Halotolerant Strain...

Halotolerant strains isolated from extreme environments rely on exopolysaccharides (EPSs) to maintain cellular integrity under high salinity and ensure survival under harsh conditions. Although continuous screening efforts have identified numerous EPS-producing halotolerant strains, research on the structural characteristics and physicochemical properties of their EPSs remains limited. In this study, an EPS-producing strain yielding 2.59 ± 0.15 g/L was isolated from saline soil and identified as Oceanobacillus sp. DT-Z6. The optimal conditions for key fermentation parameters were determined using a one-factor-at-a-time approach, resulting in a maximum EPS yield of 6.65 ± 0.06 g/L. EPSs produced under optimized conditions were extracted by ethanol precipitation and further purified using anion-exchange chromatography and gel filtration chromatography, yielding two novel EPS fractions, EPS6-0 and EPS6-1. The purified EPSs were characterized using monosaccharide composition analysis, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The results indicated that both EPS6-0 and EPS6-1 were levan-type fructans containing β-(2, 6) linkages, with molecular weights of 1.17 × 10⁸ g/mol and 5.93 × 10⁷ g/mol, respectively. Physicochemical analysis revealed that EPS6-0 and EPS6-1 exhibit narrow size distributions in solutions, diverse micro-morphologies, and excellent thermal stability. Collectively, these findings provide a foundation for understanding structure-function relationships in EPSs from this halotolerant strain and support their potential industrial applications.