Key Points:
- Microbiologists have previously studied the bacterial species found in subway stations, but fungi have often been overlooked.
- An international team of researchers collected monthly samples from subway stations in Beijing and found high fungal diversity, mostly non-pathogenic. Some opportunistic pathogens were also detected.
- Fungal communities were observed to vary significantly by season and station types.
- The work could guide better strategies for air quality control in urban transit systems.
Washington, D.C. — Subways don't just bring people together. They're also a hub of microbial activity, including fungi. Over the course of a year, an international team of researchers collected air samples from 15 stations in the Beijing subway network, one of the largest in the world, and cataloged the fungal species they found.
This week in Microbiology Spectrum , they report their findings. Their analyses turned up a highly diverse community—spanning 270 genera—that varied not only by season but also by whether a station was an interchange connecting lines, a suburban station or some other type.
The bacterial microbiome of the subway environment has been well documented and analyzed in previous studies looking at subway systems, including those of Hong Kong, New York City and Boston, said Jun-min Liang, Ph.D., at the Institute of Microbiology, Chinese Academy of Sciences, who led the study. Fungal communities in transit hubs, however, have received less attention until now.
With the new study, Liang said, "we convert from a bacterial-centric perspective to a more comprehensive '2-kingdom' understanding of transit micro-ecology." This broader view of subway microbial communities, she said, could enhance public health initiatives—such as improved pathogen detection. This deeper understanding could also support efforts to improve air quality, because fungi, compared to bacteria, are more easily dispersed through air currents.
The research group had previously studied fungal diversity, particularly plant pathogens, in agricultural settings where grains, soils and seeds interact with microorganisms. "Subways represent a unique extreme," noted Liang. "They constitute an almost enclosed, human-made biome built of steel and concrete." By comparing these distinct environments, researchers can test whether the ecological patterns observed in agricultural systems also hold true in subterranean transit ecosystems.
From October 2021 to September 2022, the researchers collected samples every month from air filters at 15 stations in the Beijing subway network. They sterilized the surfaces with ethanol afterward to prepare a clean surface for the next month's collection. The sites included railway and airport stations, urban hub stations (where passengers can change from one line to another), and outlying suburban stations in remote residential areas.
The researchers found that stations, often well protected tens of meters underground, harbored a core set of fungal taxa that present in most samples. Beyond those core taxa, analyses of sequencing data revealed notable variations in dominant families and genera across seasons and station types. Summer samples showed lower diversity than other seasons. At the genus level, Fusarium and Alternaria were dominant in spring and summer, whereas Aspergillus, Chaetomium, Cladosporium and Meyerozyma prevailed during autumn and winter.
"The air circulating in underground environments contains a predictable, yet seasonally dynamic, community of fungi," Liang said. This includes several opportunistic fungal pathogens that can cause human diseases. "Ventilation and particular matter controls strategies should therefore explicitly incorporate fungi, not just bacteria or chemical pollutants."
In future studies, the researchers hope to expand their findings by confirming virulence genes, screening for anti-fungal resistance and identifying which airborne fungi are most active during rush hours. They also plan to investigate whether the same seasonal and station-related patterns occur in other cities, such as Shanghai, Guangzhou and Singapore. "Addressing these will move us from description characterization to predictive management of subway mycobiomes," Liang said.
