Strongest untreated mycelium materials produced by Schizophyllum commune dikaryons

Monokaryons of Schizophyllum commune are preferred to produce mycelium materials due to their inability to form fruiting bodies and thereby producing uniform materials. However, a single gene mutation in such monokaryons can negatively impact biomass, chemical composition, and mechanical properties of the mycelium material. Dikaryons contain two instead of a single nucleus per hyphal compartment, thereby promoting higher phenotypic stability in the case of recessive mutations. Here, biomass formation and mycelium material properties of four S. commune dikaryons were compared to a monokaryon commonly used in mycelium material production. To this end, mycelium was grown in three different growth media. The monokaryon yielded a biomass of 3.11-9.31 g L^-1, an ultimate tensile strength (σ) of 4.62-7.77 MPa, a Young's modulus (E) of 0.38-0.64 GPa, and an elongation at break (ε) of 1.51-1.93%. Most dikaryons exhibited a strikingly higher σ (19.55-47.29 MPa), a similar or higher E (0.69-2.06 GPa) and ε (2.09-7.92%), and a lower or similar biomass (1.48-7.71 g L^-1). Notably, σ values up to 47.29 and 47.16 MPa were obtained for the diakaryotic S. commune strains 139 and 351, respectively, making them the strongest untreated mycelium materials reported so far. Results suggest that this high strength is caused, at least in part, by a high amount of KOH-soluble cell wall components and by low sc3 expression.