Research on air samples collected at altitudes reaching 3,000 meters above Japan has uncovered a wide variety of viable bacteria and fungi. These microorganisms are believed to have been carried by air currents from locations over 2,000 kilometers away, specifically areas with high levels of fertilizers and pesticides. The findings, published in the Proceedings of the National Academy of Sciences (PNAS), introduce a new understanding of how pathogens affecting humans, animals, and plants can spread across great distances. This investigation was spearheaded by the Barcelona Institute for Global Health (ISGlobal), supported by the “la Caixa” Foundation, along with the Daniel Bravo Andreu Private Foundation (FPDBA).
While it is known that pathogens can be transmitted through the air, there is limited knowledge regarding the types of microbes that can endure extreme altitudes with harsh conditions. “Above a particular level in the troposphere (known as the planetary boundary layer), materials can be transported over vast distances due to the isolation of the air in that area and reduced friction with the surface. However, we did not expect to find living microorganisms there,” remarked Xavier Rodó, a researcher at ISGlobal.
“This study is notable because we conducted ten tropospheric flights to investigate microbial diversity at high elevations, in contrast to most studies that have focused on heights only a few meters above ground or ocean levels,” he added.
Airborne microbes high above Japan
To conduct their research, Rodó and his international team utilized a Cessna aircraft for ten aerial surveys at altitudes ranging from 1,000 to 3,000 meters above Japan, commencing from Chofu airport near Tokyo. These flights were strategically designed to follow wind patterns from mainland Asia, known as tropospheric bridges, which transport air from far-off regions; in this case, air rising from mainland China before descending over Tokyo due to typical winter weather patterns. Moreover, ground samples were also collected at Chofu for comparison. In total, 22 aerosol filter samples were analyzed for their chemical and biological make-up during two sampling periods in February and April of 2014.
Through DNA sequencing, the team identified more than 266 fungal and 305 bacterial genera associated with the aerosols, some of which pose potential risks to human health, animals, or plants. Noteworthy bacterial species included Escherichia coli, Serratia marcescens, Clostridium difficile, Clostridium botulinum, Haemophilus parainfluenzae, Acinetobacter baumannii, and various species of Staphylococcus. Fungi from genera such as Candida, Cladosporium, and Malassezia, known to cause diseases in individuals with weakened immune systems, were also identified.
By cultivating some of the atmospheric samples, researchers demonstrated that airborne bacteria remained viable and some showed resistance to widely used antibiotics. “Surprisingly, we found that the strain of Micrococcus luteus was resistant to multiple drugs, including carbapenems, glycopeptides, ciprofloxacin, and trimethoprim-sulfamethoxazole. Our results indicate that antimicrobial resistance could potentially spread over extensive distances through this previously unrecognized method,” stated Sofya Podzniakova, co-first author of the study.
Travelling thousands of kilometers
The presence of these aerosols alongside substances like zinc sulfate and potassium, often found in fertilizers and pesticides, points to an agricultural origin, aligning with the intensively cultivated areas of northeast China.
Interestingly, the airborne and ground samples collected on the same days showed a great deal of similarity in microbial diversity, likely due to air descending from higher altitudes. Simulation of particle transport models, conducted by Roger Curcoll—now a researcher at the Universitat Politècnica de Catalunya — BarcelonaTech (UPC)—supported the possibility of these particles being transported from northeast China and the descent of tropospheric air masses towards Japan.
“Our discoveries reveal an extraordinary and previously unknown variety of microbes that are carried by wind patterns over thousands of kilometers from their origins through powerful wind tunnels present high in the troposphere,” Rodó stated. “These results represent a significant change in our understanding of how airborne pathogens can impact human health, particularly those thriving in the environment.”
While this study does not establish a direct link between the identified human pathogens in aerosols and health outcomes, it highlights the urgent need for further investigation into the long-distance spread of various microbial pathogens.
