The project investigated the influence of SC3 and SC15 gene deletion on fungal growth, extracellular secretion, and adhesion properties using four Schizophyllum commune strains: two wild types (H4-8A and 4-39) and two mutants (4-39ΔSC3 and 4-39ΔSC3ΔSC15). These strains were cultivated under both liquid shaking and agar static conditions on a range of substrates to evaluate differences in biomass morphology, extracellular polysaccharide production (notably schizophyllan), surface attachment, and bonding strength to lignocellulosic substrates.
In liquid cultures, H4-8A produced dense, spherical pellets and secreted the most extracellular material (7.43 g/L), with a high yield of precipitable schizophyllan (3.63 g/L). By contrast, 4-39 formed irregular, star-shaped pellets with limited schizophyllan production (0.27 g/L). The deletion strains, despite retaining the pellet morphology of 4-39, showed a dramatic increase in extracellular material and schizophyllan yield (up to 2.62 g/L), without a reduction in sediment biomass. This demonstrates that hydrophobin deletion enhances extracellular polysaccharide production independently of mycelial growth.
Under static incubation, all strains fully colonized the test substrates (wood, glass, Teflon), but only the wild types developed robust aerial hyphae with superhydrophobic surfaces. The mutant strains produced flatter, hydrophilic vegetative mats with reduced aerial coverage, confirmed by water contact angle analysis.
A surface detachment assay was performed to assess mycelium attachment strength on wood, glass, and Teflon. While wet mycelium detached rapidly from non-porous substrates, dried samples adhered more strongly, with strain- and surface-specific differences. Wild-type strains remained attached at high shaking speeds on Teflon, whereas mutants detached earlier. All strains remained stably attached to wood, indicating strong physical interlocking likely due to substrate porosity.
Adhesion testing revealed strain-specific performance. In liquid cultures, ΔSC3 achieved the highest bonding strength (1.83 MPa), while in static incubation, ΔSC3ΔSC15 performed best (1.82 MPa). These differences are attributed to the altered surface composition and hydrophilic properties of the mutants. Overall, the project demonstrated that fungal adhesion can be modulated through genetic and environmental controls, offering a biologically tunable platform for adhesive development.
