The metabolic regulation mechanism of birchwood polysaccharides inducing Inonotus obliquus to synthesize bioactive polysaccharides

This study investigated the mechanism by which birch-derived polysaccharides induce extracellular polysaccharide synthesis in Inonotus obliquus under submerged fermentation conditions. Both cellulose-derived birch polysaccharide (C-48) and water-extracted hemicellulose polysaccharide (H-0) significantly increased α-glucosidase inhibitory activity of extracellular polysaccharide, with increases of 4.09 and 3.44-fold, respectively. C-48 also accelerated the synthesis of extracellular polysaccharides. These differences can be attributed to their differential capacities to activate polysaccharide-synthesizing enzymes and regulate metabolic pathways after absorption by growing mycelia. The addition of both polysaccharides inhibited phosphoglucose isomerase (PGI) activity while enhancing the activities of phosphoglucomutase and Uridine Diphosphate (UDP) -glucose pyrophosphorylase, thereby promoting metabolic flux toward UDP-glucose synthesis and increasing the production of bioactive glucans. Transcriptomic analysis revealed that polysaccharide supplementation led to downregulation of key genes involved in glycolysis and the tricarboxylic acid (TCA) cycle, while upregulating genes associated with gluconeogenesis. These regulatory shifts suppressed glucose catabolism and optimized polysaccharide biosynthesis in I. obliquus. In the C-48 group, regulation of key enzyme genes in the mannose and pentose phosphate pathways promoted the generation of polysaccharide precursors. In contrast, the H-0 group regulated genes involved in pentose interconversion, glycoside hydrolysis, and glycolysis, thereby indirectly influencing glucose metabolism and facilitating extracellular polysaccharide production. These distinct regulatory effects indicate that polysaccharides critically influence the synthesis of bioactive polysaccharides, underscoring their potential as metabolic activators.