Harnessing exogenous membrane vesicles for studying Fusarium circinatum and its biofilm communities

Abstract Extracellular vesicles (EVs) are tiny messengers that convey bioactive molecules from donor to recipient cells, leading to changes in their physiology and function. We investigated the role of EVs in shaping growth and the biofilm biology of the tree pathogen Fusarium circinatum and its interaction with the susceptible host, Pinus patula. Vesicles were collected from fungal planktonic and biofilm cultures and from pine seedling needles and roots. The physical properties of these vesicles were analysed using nanoparticle tracking analysis and transmission electron microscopy, which revealed a diverse range of sizes and shapes, respectively. Furthermore, uptake of vesicles by conidia demonstrated that F. circinatum EVs significantly but variably affected spore viability during the early phase (2-4 h) although they enhanced biomass and extracellular matrix (ECM) production in biofilms. In contrast, P. patulaEVs greatly inhibited hyphal formation and biofilm biomass, but failed to inhibit ECM biosynthesis in the fungal biofilm. Our results therefore suggest that conidial germination is essential for late fungal development including hyphal and biofilm formation while matrix production may be a counter measure against harsh environmental conditions including the effects of plant-derived EVs. Therefore, plant-microbe interactions viewed within the context of biofilm formation can improve understanding into the dynamic and complex behaviours of fungal pathogens and their interactions with plant hosts.