Selection and characterization of wood decay fungal strains for the development of mycelium-based materials

Fungi, and in particular wood decaying fungi, are being re-considered in the last few years as source for biotechnological and industrial applications. These organisms seem to be particularly suitable for developing myco-materials thanks to their chemical composition, mycelial texture, ease of cultivation, and lack of sporification. In this study 94 different strains of Agaricomycetes, belonging to 75 different species, related to 50 genera (18 families and 5 orders) were isolated using malt extract agar (MEA) medium enriched with hydrogen peroxide. Molecular analysis, extracting and amplifying the ITS region, allowed to confirm the identification of the isolated strains. Among these, twenty-one wood decaying fungal strains were chosen on the base of colour, homogeneity, and consistency of the mycelium. The growth rate of each selected strain was measured and a chemical characterization of all their mycelia obtained in liquid static fermentation was determined through thermogravimetric analysis (TGA). Two different typologies of materials have been produced. One was obtained developing an exclusive method (newly patented) to improve consistency, structure and thickness of the mycelium mats: among all the strains, Abortiporus biennis 064-18, Fomitopsis iberica 104-19 and Irpex lacteus 076-18 showed to be suitable for a demo production of this material typology. The obtained mats were then analysed throw scanning electron microscopy (SEM) image processing and mechanical tests (tensile strength, elongation at break and Young modulus). On the other hand, the second kind of material was obtained using fungal strains characterised by their hyphal cell wall chemical composition: highest content of α-glucans, β-glucans or chitin as well as a high growth rate. Five strains out of the twenty-one selected were chosen to evaluate how these differences could influence the mechanical and chemical characteristics of the resulting material. These five fungal strains were cultivated in liquid submerged dynamic fermentation (both flasks and bioreactor). Then, chitin and glucans were extracted and crosslinked with acetic acid and plasticized with glycerol in order to obtain flexible sheets. In the end, Abortiporus biennis 064-18, Fomitopsis iberica 104-19 and Stereum hirsutum 073-18 were able to produce this kind of material. Thermogravimetric analysis (TGA) allowed to evaluate the principal chemical components of the materials, providing a semi-quantitative indication on mat composition. The material obtained from each species was also mechanically tested (tear strength, elongation at break, and Young’s modulus) showing quite different results. In conclusion, two typologies of sustainable and 100% biobased pure fungal-based row materials have been produced from different wood decaying fungal strains. Further chemical and physical steps are needed in order to let these materials show their high potential in practical applications. This project represents a valuable and in-depth analysis of alternative suitable wood decaying fungal strains knowledge and an essential groundwork for any further study on this topic. Future researches have a real opportunity to significantly improve these promising myco-materials.