Scientists Have Found Bacteria and Fungi 10,000 Feet Up in the Air

When a team of Spanish and Japanese researchers chartered a plane up to 10,000 feet into Japanese airspace, their aim was to analyze the chemistry of airborne dust particles. But what they found in the air samples were microbes, many of which were still viable—and several of them could infect and be harmful to humans. Their findings were published earlier this month in the journal Proceedings of the National Academy of Sciences.

“We were not supposed to find anything like this,” Xavier Rodó, lead study author and a computational ecologist at the Barcelona Institute for Global Health, tells Popular Science’s Lauren Leffer. It’s a “detection of an unprecedented diversity of microbial taxa at heights [far above the planetary boundary layer].”

Specifically, the scientists found 266 kinds of fungi and 305 types of bacteria. Based on air currents and chemical analysis, they inferred that the microbes came from an agriculturally intensive region in China. This meant that the wind had carried them for at least 1,200 miles, unbeknownst to humans.

While previous research suggests dust can travel thousands of miles and that microbes can piggyback on dust particles, scientists were surprised to find that microbes could survive such a high-altitude and long-distance journey.

The idea to collect air samples by flight came from previous research by Rodó and others about Kawasaki disease, a rare heart condition with a mysterious origin that usually impacts young children, he tells the New York Times’ Carl Zimmer. Rodó noticed that the disease appears in surges in both Japan and California that often coincide with winds from northeast China. This suggested that something capable of causing infection might have traveled on the wind—so the team boarded a plane to find out.

As they flew, they let air flow into a filter, which trapped the microbes for study, at altitudes between 0.6 and 1.9 miles high. Even at the upper end of that range, they indeed found live microbes, and some were proven to be viable when they multiplied in Petri dishes.

Rodó tells the Guardian’s Damian Carrington that the microbes were in “ultra-low concentrations” that in most cases “wouldn’t elicit infection,” in humans. Still, the findings have implications for human health. For example, some of the microbes carried drug-resistant genes, which is a troubling discovery given the context of a global rise of antimicrobial resistance.

“What is clear is that there is this biodiversity seeding across far distances,” Rodó tells Popular Science. “Of course, if the bugs that are distributed have resistant genes, then you now have those being introduced into a new community, which could be worrisome.”

“I am surprised by the number of human pathogens that they revealed,” David Schmale, an aerobiologist at Virginia Tech who did not participate in the research, tells the New York Times. He adds that the best way to study them would be to infect human cells or lab animals, which is something the team plans to do, using human lung cells.

The study hasn’t solved the puzzle of what causes Kawasaki disease. But it does raise new research questions, including how the microbes stay alive while being carried so high on the wind and whether winds can spread diseases.

“This is something that deserves attention,” Rodó says to the New York Times.

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.