Flexible Fungal Materials: Shaping the Future.

Fungi are a revolutionary, smart, and sustainable manufacturing platform that can be used to upcycle byproducts and wastes into flexible fungal materials (FFMs) such as chitin- and ß-glucan-based foams, paper, and textiles. With highly adaptable manufacturing pathways, the efficiency and properties of these materials depend on the biomass source and fermentation method. Liquid substrates provide fast, upscalable, and compact production processes but are susceptible to contamination and are limited to paper-like materials for printing, wound dressings, and membranes. Solid-state fermentation is cheaper but struggles to deliver homogeneous fungal growth and is used to produce fungal foams for packaging, insulation, textiles, and leather substitutes. The broad range of applications and uses of biological organisms in materials hallmarks fungi as forerunners in improving environmental sustainability globally.

Characterization of the cell wall of a mushroom forming fungus at atomic resolution using solid-state NMR spectroscopy.

Cell walls are essential in the interaction of fungi with the (a)biotic environment and are also key to hyphal morphogenesis and mechanical strength. Here, we used solid-state NMR (ssNMR) spectroscopy combined with HPLC and GC-MS to study the structural organization of the cell wall of a representative of the Basidiomycota, one of the two main phyla of fungi. Based on the data we propose a refined model for the cell wall of a basidiomycete. In this model, the rigid core is built from α- and ß-(1,3)-glucan, ß-(1,3)-(1,6)-glucan, highly branched and single stranded ß-(1,4)-chitin as well as polymeric fucose. The mobile fraction of the cell wall is composed of ß-(1,3)-glucan, ß-(1,3)-(1,6)-glucan, ß-(1,6)-glucan, α-linked reducing and non-reducing ends and polymeric mannose. Together, these findings provide novel insights into the structural organization of the cell wall of the model basidiomycete S. commune that was previously based on destructive chemical and enzymatic analysis.

Fungal mycelium classified in different material families based on glycerol treatment.

Fungal mycelium is an emerging bio-based material. Here, mycelium films are produced from liquid shaken cultures that have a Young's modulus of 0.47 GPa, an ultimate tensile strength of 5.0 MPa and a strain at failure of 1.5%. Treating the mycelial films with 0-32% glycerol impacts the material properties. The largest effect is observed after treatment with 32% glycerol decreasing the Young's modulus and the ultimate tensile strength to 0.003 GPa and 1.8 MPa, respectively, whereas strain at failure increases to 29.6%. Moreover, glycerol treatment makes the surface of mycelium films hydrophilic and the hyphal matrix absorbing less water. Results show that mycelium films treated with 8% and 16-32% glycerol classify as polymer- and elastomer-like materials, respectively, while non-treated films and films treated with 1-4% glycerol classify as natural material. Thus, mycelium materials can cover a diversity of material families.

Hydrophobin gene deletion and environmental growth conditions impact mechanical properties of mycelium by affecting the density of the material.

Filamentous fungi colonize substrates by forming a mycelium. This network of hyphae can be used as a bio-based material. Here, we assessed the impact of environmental growth conditions and deletion of the hydrophobin gene sc3 on material properties of the mycelium of the mushroom forming fungus Schizophyllum commune. Thermogravimetric analysis showed that Δsc3 mycelium retained more water with increasing temperature when compared to the wild type. The Young's modulus (E) of the mycelium ranged between 438 and 913 MPa when the wild type strain was grown in the dark or in the light at low or high CO2 levels. This was accompanied by a maximum tensile strength (σ) of 5.1-9.6 MPa. In contrast, E and σ of the Δsc3 strain were 3-4- fold higher with values of 1237-2727 MPa and 15.6-40.4 MPa, respectively. These values correlated with mycelium density, while no differences in chemical composition of the mycelia were observed as shown by ATR-FTIR. Together, genetic modification and environmental growth conditions impact mechanical properties of the mycelium by affecting the density of the mycelium. As a result, mechanical properties of wild type mycelium were similar to those of natural materials, while those of Δsc3 were more similar to thermoplastics.

Impact of salicylic acid- and jasmonic acid-regulated defences on root colonization by Trichoderma harzianum T-78.

We recently found that the beneficial fungus Trichoderma harzianum T-78 primes tomato plants for salicylic acid (SA)- and jasmonic acid (JA)-regulated defenses, resulting in enhanced resistance against the root knot nematode Meloidogyne incognita. By using SA- and JA-impaired mutant lines and exogenous hormonal application, here we investigated whether the SA- and JA-pathways also have a role in T-78 root colonization of Arabidopsis thaliana. Endophytic colonization by T-78 was faster in the SA-impaired mutant sid2 than in the wild type. Moreover, elicitation of SA-dependent defenses by SA application reduced T-78 colonization, indicating that the SA-pathway affects T-78 endophytism. In contrast, elicitation of the JA-pathway, which antagonized SA-dependent defenses, resulted in enhanced endophytic colonization by T-78. These findings are in line with our previous observation that SA-dependent defenses are repressed by T-78, which likely aids colonization by the endophytic fungus.