Seasonal Variations and Spatial Distribution of Indoor Airborne Microorganisms in a University Campus in Beijing: A Metagenomic Study

As densely populated urban areas, the spatiotemporal distribution characteristics of airborne microorganisms on university campuses are critical to the health of students and faculty, as well as urban ecological safety. This study employed impact sampling and metagenomic sequencing techniques to systematically analyze the concentration, particle size distribution, and community characteristics of airborne microorganisms across different seasons (autumn, winter) and sites (male dormitory, female dormitory, classroom, computer room) at the Shunyi Campus of Capital Medical University. The average concentration of airborne microorganisms was 553.38 ± 277.06 CFU/m³. Concentrations varied by location, ranking from highest to lowest as: male dormitory (598.18 ± 314.59 CFU/m³) > computer room (566.55 ± 248.40 CFU/m³) > classroom (555.80 ± 246.19 CFU/m³) > female dormitory (495.09 ± 258.27 CFU/m³). Microbial concentration in winter (696.55 ± 306.36 CFU/m³) was significantly higher than in autumn (410.20 ± 138.94 CFU/m³, P  < 0.001), with particle sizes predominantly concentrated between 0.65–2.1 µm (Stages VI and V). Metagenomic analysis revealed Bacillota (52%) and Pseudomonadota (19%) as the dominant phyla. Species diversity was significantly higher in winter than in autumn (Shannon index, P  = 0.02), with the classroom exhibiting the highest number of species (2155). Opportunistic pathogens, such as Stutzerimonas stutzeri , were detected. Principal Coordinate Analysis (PCoA) and PERMANOVA indicated that seasonal variation was the primary driver of community structure (R²=0.152, P  = 0.003), with location having a lesser impact. These findings demonstrate that both seasonal shifts and human activity shape the airborne microbiome in university indoor environments and provide a scientific basis for indoor air quality management and microbial risk prevention strategies in campus settings.