Structural Characterization and Immunological Activity of Polysaccharides Extracted from Ulva pertusa Fermented by Bacillus velezensis

Abstract Ulva pertusa polysaccharide is a sulfated heteropolysaccharide, but its high molecular weight has led to an unclear understanding of its bioactive mechanisms. In this study, a fermented polysaccharide, UBV-1, was obtained through cofermentation of U. pertusa powder with Bacillus velezensis, followed by separation and purification. Its structure was further elucidated by GC-MS and NMR. The results showed that UBV-1 enhanced the expression of tight junction proteins in human intestinal epithelial cells (HIEC-6), and both the polysaccharide itself and the metabolites produced by HIEC-6 cells stimulated with UBV-1 promoted the activation of THP-1 macrophages. Mechanistic studies indicated that this immunomodulatory effect is associated with activation of the NLRP3 inflammasome and promotion of mature IL-1β release. This study provides a green and efficient method for preparing U. pertusa polysaccharide and offers a theoretical foundation for its application as a raw material in functional foods.