In situ interfacial shear rheology of fungal films

Understanding the dynamic film formation of fungi is essential for designing and creating engineered living fungal materials. However, conventional growth measurements often neglect the three-dimensionality of fungal growth and thus only provide scarce information about the transient mechanical properties. In this study, we use interfacial shear rheology (ISR) to investigate the dynamic formation of fungal films. By using ISR we can identify the lag, exponential and stationary phases of fungal growth by measuring the film viscoelasticity. We observed an increase in storage modulus after 2 h before spore germination, most likely caused by the absorption of spores and metabolic by-products during swelling and germination. Modifying the sugar concentration in the liquid growth media allowed for delayed germination while enhancing the exponential propagation speed of fungi, as visible through colony diameter measurements, spectrophotometry and ISR. Furthermore, we were able to observe the film formation through an increase in interfacial moduli as a measure of biomass. In combination with spectrophotometry and colony diameter measurements, ISR provides a complete picture of the transient film formation over 3 days, shedding light on the germination, exponential growth and stationary phase by providing non-destructive, qualitative measures for biomass and quantitative measures for film strength.