A novel lattice-based model for investigating three-dimensional fungal growth on solid media

Filamentous fungi can regulate their growth mechanisms to adapt to the environment and form different morphologies. On solid media, their first action is generally to adhere to a surface and form an approximately planar shape on a flat substrate. In a three-dimensional (3D) modelling approach, this environment is therefore heterogeneous along the z-direction. To clarify the interactions between hyphal behaviours and this heterogeneous environment, a 3D discrete model was developed. This model applied a special lattice-based approach which eliminates the restriction of lattice configuration to the simulated mycelia networks while maintaining high computational efficiency. It incorporates explicitly the mechanisms of hyphal elongation, apical and lateral branching, anastomosis and tropism, and is rigorously validated by the experimental data on Postia placenta growth on malt extract agar. Results compared with experimental data showed that the presence of substrate at z=0 bends the extension direction of hyphae towards the substrate surface. To mimic the experimental data, the bending rate was determined by an exponential-like tropism. Moreover, the branching direction was also constrained on the stage of its emergence. Compared to a simpler 2D model, the simulations of the 3D model were closer to actual growth, hence leading to a realistic mycelial network in terms of both configuration and biomass density. This 3D model can be easily extended to investigate fungal growth in other scenarios, such as for solid-state fermentation in incorporating hyphal penetration, in obstructed environments and even in wood panels.