Biofilm characterization in the maize pathogen, Fusarium verticillioides

Nearly all microbes, including fungal pathogens, form biofilms, which are structured communities of microbial aggregates enclosed in self-produced extracellular polymeric substances (EPS) and attached to a surface. Studying plant-associated fungal biofilms can enhance understanding of fungal biology and knowledge of the links between fungal diseases and plants. However, only a few plant-associated fungi are reported to form biofilms. This study aimed to examine the ability of a mycotoxigenic fungus of maize, Fusarium verticillioides, to form biofilms under laboratory conditions. During our investigation, F. verticillioides stationary phase cultures incubated in liquid media developed a biofilm-like pellicle with a hyphal assemblage that appears in the form of a cloudy and thin slime material. Under the microscope, the biofilms exhibited a highly heterogeneous architecture made of dense, entangled, and compact hyphae, which were accompanied by a quantifiable EPS and extracellular DNA (eDNA). The biofilm was also found to respond to different abiotic conditions including pH and temperature, suggesting their relevance in a field setting. We further demonstrate the biofilm structural maintenance role of eDNA through treatment with DNase, which was only marginally effective during late biofilm stages, suggesting that it forms complex interactions with the EPS during biofilm maturation. Based on these results, we propose that F. verticillioides forms a true biofilm that may act as a potential virulence factor.