Air samples collected at altitudes of up to 3,200 kilometers above Japan contained a surprising variety of living microbes, such as bacteria and fungi, many of which are toxic to humans.
And not just the local ones. Some of these microbial stowaways have traveled more than 1,000 miles on aerosols from areas rich in fertilizers and pesticides.
This has thrown the scientific world into a flurry of questions about the travel of human, animal and plant pathogens across vast geographic territories, invisible to the naked eye.
This microbial exploration was carried out by the Barcelona Institute of Global Health (ISGlobal), with the support of the Daniel Bravo Andreu Private Foundation (FPDBA).
Microbes travel through the air
It’s not uncommon for pathogens to travel on the wind. But the diversity of microbes that can survive at high altitudes, where conditions might give even an Everest climber pause, is a new revelation.
“We know that beyond a certain point in the troposphere (called the planetary boundary layer), some materials can be transported over long distances because the air in that region is isolated from the surface and there is less friction. But we did not suspect that viable microorganisms could also be found there,” explains Xavier Rodó, ICREA researcher at ISGlobal.
Rodó and his team conducted ten tropospheric flights to examine microbial diversity at high altitudes, a significant advance over studies usually carried out just a few meters above the ground or ocean.
Tracing the microbial path
Rodó and his international team boarded a Cessna plane and conducted aerial surveys over Japan, following wind currents coming from the Asian continent.
These transcontinental airways, called tropospheric bridges, connect air from distant parts of the world.
To put this into context, think of air rising over mainland China and then falling over Tokyo, due to typical winter weather conditions.
A total of 22 aerosol filter samples were collected during two periods (February and April 2014), methodically analyzed for their chemical and biological composition.
By sequencing the DNA of the samples, the team identified more than 266 fungal genera and 305 bacterial genera associated with the aerosols.
Types of Microbes in the Air
This microbial soup included potential pathogens for humans, animals and plants — familiar names like Escherichia coli, Serratia marcescens, Haemophillus parainfluenzaeand several Staphylococcus the species were part of the bacterial mixture.
Fungal factions included genera like Candida and Cladosporium, to name a few.
“Surprisingly, the Yellow micrococcus “The isolated strain was resistant to several drugs, including carbapenems, glycopeptides, ciprofloxacin and trimethoprim-sulfamethoxazole,” explains Sofya Podzniakova, co-first author of the study.
“Our results suggest that antimicrobial resistance could spread over long distances via this previously unknown pathway,”
Tropospheric movement tunnel of airborne microbes
If you’re curious about the origin of these airborne pathogens, the answer might be right under our noses – or rather, under our feet.
The presence of elements such as zinc sulfate and potassium, commonly found in fertilizers and pesticides, suggests an agricultural origin. A scenario quite consistent with the extensively cultivated lands in northeastern China.
Samples taken at high altitude and on the ground during the days studied showed a striking similarity in microbial diversity. A consequence of the air sinking from altitude to the ground, perhaps?
Particle transport models simulated by Roger Curcoll, currently a researcher at the Universitat Politècnica de Catalunya — BarcelonaTech (UPC), would certainly support this theory.
New chapter in the study of microbe transport
The implications of this study are profound. “Our results reveal a rich and unprecedented diversity of microbes that are dispersed by wind currents thousands of kilometers from their source through intense wind tunnels that form in the upper troposphere,” Rodó said.
“They represent a paradigm shift in our understanding of how human health can be affected by pathogens that thrive in the environment, particularly in the air.”
Although there is not yet a direct link between the presence of known human pathogens in aerosols and their health effects, the study affirms the urgent need to further explore the long-distance movement of airborne microbes and microbial pathogens.
So the next time you feel the wind on your face, remember that it has stories to tell: stories of microbes that climb the troposphere and cross continents. The pathogens that travel the globe show us how interconnected our world is, even in invisible ways.
The study is published in the journal Proceedings of the National Academy of Sciences.
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