A Snap-Shot Metabarcoding Survey of Fungal Diversity at the Intersection of the Atmosphere and the Danube River

Fungi represent one of the most diverse groups of organisms and inhabit multiple environmental compartments, including the atmosphere, where they occur as highly mobile biological particles. The atmosphere is increasingly recognized as an active ecological compartment integrating signals from terrestrial and aquatic ecosystems, yet interactions between air and freshwater communities of fungi remain insufficiently explored. This study provides a one-day snapshot into mycobiome diversity at the intersection of the atmosphere and the Danube River influenced by sewage water inflow. Mycobiome diversity is determined by environmental DNA (eDNA) analysis. The study discusses the potential exchange of taxa between air, water and sediment. eDNA was extracted from air, river water (at a sewage outlet, upstream and downstream of it), and river sediment samples, while full-length ITS amplicon sequencing was applied to analyze fungal community composition and diversity. Airborne fungi and those from the sewage samples showed lower overall diversity and more pronounced dominance of a few taxa when compared to water and sediment samples. Despite differences, many taxa were shared among environments, suggesting connectivity and possible bidirectional exchange. Several taxa detected in the air were associated with soil, vegetation, and sewage, including fungi of potential environmental and health relevance. Our results demonstrate the detection of notable fungal diversity across interconnected environments, suggesting that both air and aquatic systems contribute to the exchange of fungi. Urban wastewater is discussed as a possible localized source of airborne fungi with potential environmental and public health implications.