Structural characteristics and immunomodulatory activity of an exopolysaccharide from Antarctic Pseudoalteromonas sp. LP6-12-2.

Natural polysaccharides from microorganisms have various biological activities. However, those from psychrophiles with immunomodulatory properties have rarely been found. In this study, an immunoactive exopolysaccharide was extracted from Antarctic Pseudoalteromonas sp. LP6-12-2 (EPS1-1), which isolated using DEAE-Sepharose Fast Flow, Sephadex G-75, and Sephadex G-100. EPS1-1, with a molecular weight 23.47 kDa, was composed of mannose, glucose, galactose, glucosamine, and galactosamine in the ratio of 83.1:7.2:4.3:4.2:1.2. Furthermore, EPS1-1 was found to have a main chain composed of α-D-Manp (1→2) and side chains composed of α-D-Manp (1→6) by FT-IR, methylation, and NMR analyses. Besides, through the Congo red test and I₂-KI reaction analyses, it was revealed that EPS1-1 lacked triple-helix structure and had more branches. Additionally, EPS1-1 could significantly advance the proliferation, phagocytosis, acid phosphatase activity, and cytokines production of macrophage cells. Data suggested EPS1-1 demonstrated potential as an immunomodulator for functional food or pharmaceutical development.