- Polysaccharides from fungi represent a structurally diverse and biologically significant class of natural macromolecules that play essential roles in fungal physiology while also offering wide-ranging applications in medicine, food, and biotechnology.
- Fungal polysaccharides are generally categorized into structural polysaccharides, which are components of the fungal cell wall (e.g., chitin, β-glucans, mannans), and storage polysaccharides, which serve as energy reserves (e.g., glycogen, trehalose, and pullulan). Their complexity arises from varied monosaccharide compositions, glycosidic linkages, branching patterns, and molecular weights, leading to distinct biological activities and physicochemical properties.
- Within the fungal cell wall, polysaccharides are critical for maintaining rigidity, protecting against environmental stresses, and mediating interactions with the host in pathogenic species. Chitin, a linear polymer of N-acetylglucosamine, is a key structural element that provides strength and stability. Interwoven with chitin are β-glucans, particularly β-(1→3)- and β-(1→6)-glucans, which contribute to wall flexibility and integrity. Mannans and mannoproteins, often attached to cell wall proteins, play roles in adhesion and immune interactions. The dynamic remodeling of these polysaccharides allows fungi to adapt to environmental conditions and evade host immune defenses.
- From a biomedical perspective, fungal polysaccharides are renowned for their immunomodulatory, antioxidant, antimicrobial, and anticancer activities. Among the most studied are β-glucans, found in mushrooms such as Lentinula edodes (shiitake), Ganoderma lucidum (reishi), and Grifola frondosa (maitake). These β-glucans stimulate the innate immune system by binding to receptors such as dectin-1, complement receptor 3 (CR3), and toll-like receptors (TLRs) on macrophages, dendritic cells, and neutrophils. This immune priming enhances pathogen clearance and has been linked to anti-tumor effects. Other fungal polysaccharides, like heteropolysaccharides containing galactose, fucose, or uronic acids, exhibit diverse bioactivities, including antiviral, hepatoprotective, and cholesterol-lowering effects.
- In the food and nutraceutical industries, fungal polysaccharides are valued as dietary fibers, prebiotics, and bioactive ingredients. Edible mushrooms provide β-glucans and other polysaccharides that not only improve gut microbiota composition but also promote metabolic health. Fermentable fungal polysaccharides can stimulate beneficial bacteria such as Bifidobacterium and Lactobacillus, contributing to gut and immune homeostasis. Beyond health benefits, polysaccharides like pullulan (from Aureobasidium pullulans) are exploited for their film-forming and stabilizing properties, making them useful in food packaging, pharmaceuticals, and coatings.
- Fungal polysaccharides also have growing importance in biotechnology and materials science. Their biodegradability, biocompatibility, and ability to form hydrogels or films make them attractive for drug delivery, wound healing, and tissue engineering applications. For example, fungal chitosan (derived from fungal chitin) is used as a biopolymer for drug encapsulation, water purification, and antimicrobial coatings. In agriculture, fungal polysaccharides are explored as biofertilizers and plant immune stimulants, improving crop resilience against pathogens.
- In pathogenic fungi, capsular and secreted polysaccharides can act as virulence factors. For example, Cryptococcus neoformans produces a polysaccharide capsule rich in glucuronoxylomannan (GXM), which suppresses host immune responses and facilitates persistence in the host. Similarly, the cell wall polysaccharides of Candida albicans play a critical role in immune evasion and biofilm formation, underscoring the dual roles of these molecules in fungal biology and pathogenesis.
