Functions of cell wall components of Schizophyllum commune

The thesis examines the cell wall composition of the mushroom-forming fungus Schizophyllum commune in response to environmental conditions and genetic differences, as well as the functional roles of its components. Each chapter contributes distinct insights into this subject. Chapter 2 demonstrates that the cell wall of S. commune binds various ions, including Ca²⁺, Mg²⁺, Mn²⁺, NO₃⁻, PO₄³⁻, and SO₄²⁻, at significant levels (>1 mg per gram dry weight). It also binds smaller quantities of BO₃⁻, Cu²⁺, Zn²⁺, and MoO₄²⁻. Ion release was achieved by reducing the pH to 4, with efficiencies between 46% and 93%. Binding occurs at protein and β-glucan sites, with anions attaching to these and to metal ions in the wall. This mechanism may function as a storage system, limit nutrient availability to competitors, or prevent toxic influx into the cytoplasm. Chapter 3 investigates schizophyllan, a water-soluble β-glucan, across 55 S. commune strains in various media. Production varied widely, and the addition of phosphate buffer reduced both water-soluble and rigid schizophyllan levels in liquid and agar cultures. Schizophyllan was found to protect the fungus from bacterial threats and freezing conditions, highlighting its ecological and functional significance. Chapter 4 examines the predicted β-(1-3)-glucan synthase gene, fks1. Its inactivation in S. commune led to reduced biomass, less schizophyllan release, and altered cell wall composition. Specifically, rigid cell walls of the mutant strain Δfks1 had decreased schizophyllan but increased α-(1-3)-glucan and chitin. The mobile fraction contained more amino acids and lipids but lacked (N-acetyl)galactosamine. These findings underline the central role of fks1 in cell wall synthesis and integrity. The mechanical properties of wild-type and Δfks1 mycelium were assessed under various medium conditions in Chapter 5. Water uptake, attachment to tomato seeds, and cell wall composition were analyzed. Results showed that mycelium properties can be modified through cultural and processing adjustments, as well as genetic alterations. The findings also highlight the potential of S. commune cell walls as a sustainable material for seed coating, emphasizing its broader ecological and industrial applications. In conclusion the thesis provides a comprehensive exploration of S. commune cell walls, shedding light on their chemical interactions, protective roles, genetic underpinnings, and potential applications. These insights contribute to understanding fungal biology and pave the way for sustainable innovations in agriculture and materials science.