Marine influence on airborne bacterial community composition and predicted functional potential in coastal zones: a case study from Ostend, Belgium

Airborne bacteria in coastal zones and the marine influence on them remain poorly understood. Here, we investigated airborne bacterial communities at a coastal site in Ostend, Belgium, during late spring and summer using Nanopore full-length 16S rRNA gene sequencing. By comparing glass and quartz fiber filters across multiple sampling durations, we found that quartz filters with 4-12 h sampling provided sufficient DNA while avoiding longer sampling durations that may introduce bias. These samples were characterized by air mass trajectories, environmental conditions, and comparison with bacteria detected in local seawater. Air mass origin and temperature were associated with bacterial community composition. Samples associated with oceanic air masses, particularly under conditions favorable for sea spray aerosol generation, tended to show greater overlap with bacteria detected in local seawater. Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota predominated across samples. Marine-influenced aerosols tended to show higher relative abundance of Gammaproteobacteria and higher predicted representation of pathways related to protein export and diverse metabolic processes, whereas less marine-influenced samples showed greater representation of chemotaxis- and xenobiotic-associated metabolism pathways. Potential habitat affiliations suggested stronger ocean-related signatures in marine-influenced aerosols and broader terrestrial affiliations in less marine-influenced samples. These findings highlight marine-terrestrial interactions in shaping coastal airborne bacterial communities.