Effect of Low-Frequency Alternating Magnetic Field-Assisted Liquid Fermentation on Extracellular Polysaccharides Structural Characteristics and Biosynthesis of Pleurotus citrinopileatus

Low-frequency alternating magnetic field (LF-AMF) was applied to liquid fermentation of Pleurotus citrinopileatus for the production of extracellular polysaccharides (EPS). Two types of EPS (POL1 and POL2) were secreted by P. citrinopileatus under normal fermentation conditions, while only one type of EPS (POL3) was produced under LF-AMF-assisted fermentation. The study demonstrated that LF-AMF-assisted fermentation altered the monosaccharide composition, molar ratios of component monosaccharides, and molecular weight distribution of EPS. LF-AMF enhanced the flocculation activity of EPS in a concentration-dependent and dosage-specific manner. Transcriptomic analysis revealed a total of 32,413 differentially expressed genes (DEGs) (|log2(fold-change)| ≥ 1, p < 0.05) between P. citrinopileatus under LF-AMF-assisted fermentation and normal fermentation. Of those, 5818 genes were up-regulated and 26,595 genes were down-regulated. The DEGs were enriched in metabolic pathways and biosynthesis of secondary metabolite. Genes involved in glycolysis and gluconeogenesis, such as hexokinase, 6-phosphofructokinase, fructose-1,6-phosphate aldolase, glyceraldehyde 3-phosphate dehydrogenase and glucose-1,6-diphosphatase were up-regulated. Additionally, genes in the tricarboxylic acid (TCA) cycle, including citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase were also up-regulated. These findings suggest that LF-AMF-induced transcriptional alterations in glycolysis may modulate the metabolic supply of precursors for EPS biosynthesis, thereby affecting the biosynthetic process and altering the compositional characteristics of EPS.