Structural and Immunomodulatory Changes in Mycelial and Exopolysaccharides from <i>Monascus purpureus</i> M9 after Mutation of the α-1,3-Glucan Synthase Gene

The molecular structures and immunomodulatory effects of mycelial polysaccharides (MPSs) and exopolysaccharides (EPSs) from wild-type (WT) <i>Monascus purpureus</i> M9 and its α-1,3-glucan synthase gene (<i>ags1</i>) mutant strains (Δags1: gene deletion; ags1^OE: gene overexpression) were compared in this study. Mycelial aggregation was reduced in Δags1 and increased in ags1^OE, confirming the positive regulatory role of α-1,3-glucan. The EPS content was significantly higher in Δags1 and lower in ags1^OE, whereas the MPS contents showed the opposite trend. The relative content of galactomannan in the MPSs and EPSs increased in the following order: ags1^OE < WT < Δags1 and Δags1 < WT < ags1^OE. In RAW 264.7 cells, MPSs and EPSs from both WT and mutant strains enhanced the cell viability and promoted NO and cytokine (interleukin-6 and tumor necrosis factor-α) secretion. Notably, Δags1-MPS and ags1^OE-EPS exhibited enhanced immunomodulatory effects compared to those from WT, likely due to their higher galactomannan contents.