Dynamic airborne mycobiome in the metropolitan city transit system is driven by seasonality and station type.

Subway transit systems serve as the primary transportation mode in metropolitan areas. The quality of the airway in transit plays a crucial role in human health as commuters and workers are exposed to microbes transmitted from passengers and circulated within built environments. The diversity and dynamics of bacterial microbiome in these environments have been relatively well studied. However, the fungal communities remain poorly investigated. In this study, we conducted a year-long comprehensive investigation of the mycobiomes within the world's second largest subway system and analyzed the seasonal dynamics of fungal composition across intercity hub stations, urban hub stations, and suburban stations. We found a high diversity of the subway mycobiome that varied seasonally and was influenced by various environmental factors, such as particulate matter (PM2.5) levels and average humidity. Fungal diversity was higher in months with elevated PM2.5 pollution. Autumn exhibited increased diversity and peaks in the distribution of human pathogenic fungi. Furthermore, it was determined that station types exert a significant influence on the diversity of pathogenic fungi, with interchange stations (train and airport transfer stations) showing the highest diversity, while suburban stations showed the lowest. The core taxa of the mycobiome comprised several genera including ubiquitous fungi commonly found in soil and outdoor environments (e.g., Alternaria and Cladosporium), as well as potential plant and human pathogens (e.g., Phoma and Fusarium), indicating a potential risk to public health. Our study demonstrated the seasonal and spatial dynamics of mycobiomes in the Beijing subway system and revealed the factors/mechanisms that shape the indoor fungal communities. Understanding the patterns and processes of mycobiome community is important for infection prevention and public health management.

Importance: Respiratory infections and allergic reactions caused by airborne fungi have received considerable public attention; however, fungal communities remain poorly investigated. This research performed the first year-long investigation of airborne mycobiome in the world's largest subway system. We found that the fungal diversity peaks in autumn and at stations with higher PM2.5 levels. Intercity hubs exhibit the highest diversity of pathogenic fungi and the least seasonal fluctuation. Suburban stations revealed a reduced diversity of human pathogens but an elevated presence of plant pathogens. Core fungal taxa in subways include both common soil fungi (e.g., Alternaria and Cladosporium) and potential plant and human pathogens (e.g., Phoma, Fusarium, and Rhinocladiella) that pose potential health risks. These results are crucial for infection prevention and public health management in city transit systems.