Hydrophobins from <i>Aspergillus</i> Mediate Fungal Interactions with Microplastics

Microplastics cause negative environmental consequences such as the release of toxic additive leachates, increased greenhouse gas emissions during degradation, and threaten food chains. Microplastic particles are known to serve as a vector for the transport of microbes (fungi and bacteria) to new environments, threatening biodiversity. Robust biofilm formation makes fungi candidates for collecting and remediating environmental microplastics. However, fungal-microplastic colonization mechanisms have not yet been explored. In this work, we aim to understand which fungal molecules mediate microplastic binding. We examine the common fungal genus <i>Aspergillus</i>, which we found binds microplastics tightly, removing particles from suspension. Upon inoculation of <i>Aspergilli</i> with microplastic particles, up to 3.85 ± 1.48 g of microplastics were flocculated per gram of dry fungal biomass; this phenomenon was observed across various plastics ranging in size from 0.05 to 5 mm. Gene knockouts revealed that hydrophobins drive microplastic-fungi binding, evidenced by a decrease in flocculation relative to that of wild-type <i>Aspergillus fumigatus</i>. Moreover, purified hydrophobins flocculated microplastics independently of the fungus, validating their ability to bind to microplastics. Our work elucidates a role for hydrophobins in fungal colonization of microplastics and highlights a target for mitigating the harm of microplastics through engineered fungal-microplastic interactions.