Structure and immunomodulatory activity of polysaccharides from Fusarium solani DO7 by solid-state fermentation

Two polysaccharides, DGS1 and DGS2, were obtained by solid-state fermentation (SSF) of Fusarium solani DO7, an endophytic fungus isolated from the orchid Dendrobium officinale. Structural characterizations revealed that DGS1 consisted of arabinose, glucose, mannose and galactose with a molar ratio of 2.9:13.4:3.0:1, respectively, and contained (1 → 5)-Araf, (1 → 4)-Glcp, (1 → 6)-Glcp, (1 → 3)-Manp, (1 → 2,6)-Manp and (1 → 6)-Galp glycosidic linkages, while DGS2 was composed of arabinose, glucose, mannose and galactose in a molar ratio of 3.5:8.1:2.1:1, respectively, and contained (1 → 5)-Araf, (1 → 4)-Glcp, (1 → 6)-Glcp, (1 → 3)-Manp and (1 → 6)-Galp glycosidic linkages. Neither polysaccharide was toxic to human embryonic kidney cells or mouse RAW 264.7 macrophage cells. An immunomodulatory activity assay indicated that both polysaccharides could significantly enhance the levels of TNF-α, IL-6 and NO by activating TNF-α, IL-6 and iNOs gene expression, respectively, especially DGS2. Interestingly, DGS2 also possessed relatively high antioxidant activity. These results illustrate that, due to its cost-effectiveness and environmentally friendly features, SSF has significant potential as a commercially competitive source of natural products, including fungal polysaccharides, with immunomodulatory activity.