Shedding light on biofabrication of mycelium materials

The ongoing environmental crisis continues to steer innovation towards solutions for future needs. In this fashion, manufacturing processes powered by biology are gaining more and more traction, as is the case of mycelium materials. Utilizing the three-dimensional vegetative structure of filamentous fungi, i.e., mycelium, a wide range of cohesive materials can be generated. Despite the rising interest from industry and other stakeholders, limitations on real-life applications and scalability continue to pose problems for the implementation of mycelium-based materials. A major impediment for their development is the lack of insight on the interconnection among physiology, genetics, and mechanical properties.

Environmental parameters such as light have a major effect on fungal growth and can act as a trigger for fruiting body formation (Sakamoto, 2018). Recent studies have demonstrated that not only can light affect the properties of the mycelium mat (Appels et al., 2018), but light receptors, such as White Collar Complex, cryptochromes, and rhodopsin, for blue, red, and green light, respectively, are key agents in signal transduction for fungal morphogenesis (Corrochano, 2007; Fuller et al., 2015). However, despite their well-established effect on fructification, the biological impact of different wavelengths of light on mycelium development is yet to be described.

To address this knowledge gap, the effect of a delocalized light source of different wavelengths on fungal growth was tested in the context of material production. To this end, standardized inocula of Trametes versicolor were cultured in static liquid fermentation inside light-tight containers under seven different light conditions across the electromagnetic spectrum. After two weeks of growth, mycelium mats were harvested and the pH of the growth media was measured. Wet weight as well as dry weight after plasticization treatment were measured. Backlit pictures of the samples were processed with ImageJ for density and heterogeneity analyses.

Irradiance had a major impact on tissue development, culture pH, and mat heterogeneity. While different phenotypes were observed across different wavelengths, not all of them triggered a unique effect. pH, density and heterogeneity analyses showed distinct results for white, UV, and blue light. The rest of the wavelengths tested, namely green, red, far red, and dark, induced a similar behaviour in fungal growth with a prominent aerial development. A distinctly high correlation was found among pH and heterogeneity. Additionally, photomasking effects were found under UV exposure. It was also discovered that changes in wavelength led to different tissue developmental pathways with dissimilar glycerol uptake capabilities, which resulted in non-reliable dry biomass measurements.

Further exploration will entail the use of model species for genetic expression analysis. Then, photorreceptors, hydrophobins as well as developmental factors will be targeted. Differences in mechanical properties will be investigated through Young’s modulus, maximum strength, and tensile strain. Finally, FTIR will be performed to search potential associations among fungal cell wall biochemistry and mechanical performance.

This study addresses the effect of various wavelengths of light on fungal tissue formation. Collectively, such a multifaceted approach will shed light on how tissue development influence the properties of mycelium mats. Furthermore, this work establishes a comprehensive pipeline and paves the road for the utilization of light during biofabrication for the finetuning of fungal material performance. This project also helps unravel the intricate relationships among genetics, physiology, and material properties and contributes to the development of next-generation production processes for mycelium-based materials.