Architectural Confinement and Seasonal Forcing Shape Cross-Domain Pathogen Assemblages in Complex Built Environments

Airborne microbial pathogens in built environments (BEs) may pose potential health threats, yet the ecological mechanisms governing their assembly and persistence across interconnected architectural spaces are less studied. Here, we conducted a year-long, multi-spatial investigation across a university campus complex, sampling the exhaust outlets of three indoor environments and the adjacent outdoor inlets. By integrating the 16S rRNA gene and ITS sequencing from 437 paired bacterial-fungal samples, we characterized the spatiotemporal dynamics of airborne opportunistic pathogen-containing genera. Our study showed that spatial filtering emerged as the dominant determinant of pathogen community structure, with confined elevator environments serving as reservoirs of pathogens with limited but continuous microbial influx from surrounding spaces. Superimposed on this spatial baseline, bacterial and fungal pathogens displayed distinct seasonal dynamics. Opportunistic fungal pathogens such as Fusarium peaked during autumn and winter, possibly driven by enhanced aerosol persistence and dispersal under cooler, drier conditions. In contrast, bacterial pathogens exhibited greater temporal resilience, with key taxa such as Listeria transcribed actively during winter, predisposing them to increased relative abundance during spring. Cross-domain ecological networks further revealed the dynamic interactions among pathogens, centered on the skeletal structure mediated by the keystone fungal pathogen Aspergillus, suggesting that coordinated microbial interactions reinforced pathogen persistence across seasons. Together, our findings support a unified ecological framework in which pathogen dynamics within BEs arise from the coupled effects of spatial filtering, climatic modulation, and biotic interactions. These results provide a foundation for transitioning from static environmental control toward predictive pathogen management in BEs. ImportanceBEs are the primary settings of human microbial exposure, yet the ecological principles governing the persistence of airborne pathogens across interconnected indoor spaces remain poorly resolved. Most previous indoor studies have focused on isolated environments or single microbial groups, limiting our understanding of how pathogens are maintained and redistributed within complex architectural systems. By integrating bacterial and fungal community dynamics across spatial environments over four seasons, this year-long study demonstrates that the ecology of airborne pathogens is not static, but is instead dictated by a complex interplay of spatial, climatic, and biological forces. Our findings identify enclosed, high-transit elevator spaces as critical hotspots for pathogen accumulation and highlight the role of seasonal ecological reorganization in driving airborne health risks. More broadly, this work establishes a systems-level ecological framework for understanding airborne pathogen dynamics in BEs and provides a conceptual basis for developing more adaptive strategies for indoor microbial risk management.