雷雨云中的微生物大军

RENEE MONTAGNE, HOST: Microbes, those microscopic organisms that are all around us, are able to thrive in extreme environments, from deep inside volcanoes to the bottom of the ocean. And scientists have found a surprising number of them living high above us in storm clouds.

As NPR's Veronique LaCapra reports, these newly-discovered microbes could play a role in global climate.

VERONIQUE LACAPRA, BYLINE: It's been known for a long time that there are microscopic life forms floating around high above our heads. Researchers have collected them from the air above rainforests and mountains. They've found them in snow and hail. And since the 1920s, they've sometimes used planes to collect samples.

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UNIDENTIFIED MAN: He made it. Charles A. Lindbergh, Lucky Lindy as they call him, landed at Le Bourget airport, Paris, at 5:24 this afternoon.

LACAPRA: Even Charles Lindbergh tried his hand at aerial microbiology. Six years after his historic trans-Atlantic flight, he used a tube-shaped contraption called a sky hook to collect fungi and pollen from a red-winged monoplane. But most sampling efforts to date have been over land and close to the Earth's surface.

Athanasios Nenes, who's an atmospheric chemist at the Georgia Institute of Technology, says we still don't know much about what microbes are living high up in the atmosphere, or way out over the ocean. To find out, Nenes had some of his students hitch a ride on a NASA airplane that was on a mission to study hurricanes. They made multiple flights, and were able to collect air samples from about 30,000 feet, over both land and sea. The samples turned out to contain some fungi and a lot of bacteria.

ATHANSIOS NENES: And this was a big surprise because we didn't really expect to see that many bacteria up there.

LACAPRA: It's not exactly a friendly place. It's cold, it's dry, and there's a lot of damaging UV light. But Nenes says the bacteria seemed to be able to handle it.

NENES: They were alive. More than 60 percent of them were actually alive. And they were in an active state that, you know, you could say they should be metabolizing and eating things that are up there.

LACAPRA: Back on the ground, other members of the research team used genetic techniques to identify the bacteria.

KOSTAS KONSTANTINIDIS: We were able to see at least, you know, close to 100 different species, of which about 20 were in most samples.

LACAPRA: Kostas Konstantinidis is a microbiologist at Georgia Tech. He says some of those 100 species were from the ocean. Others came from the soil and from fresh water. There were even some E. coli, but Konstantinidis says he's not sure yet whether it's a type that makes people sick. The sample is still being analyzed.

KONSTANTINIDIS: My feeling is, it will also include pathogens. But we don't have direct evidence about that yet.

LACAPRA: He says if pathogens are getting swept up into the atmosphere, it might possibly have implications for the way diseases spread. But the vast majority of bacteria are harmless.

He says a more important implication of the study has to do with how clouds are formed. Up at around 30,000 feet, most clouds are made of ice crystals, not water droplets. To start forming, ice crystals need to grow around some kind of particle.

LYNN RUSSELL: Prior to this study, we'd had very little evidence that bacteria were a substantial contribution to the particles that are up there.

LACAPRA: Lynn Russell wasn't involved in this research. She's an atmospheric chemist at UC San Diego. She says there's still so much we don't know about how particles affect cloud formation, and how clouds affect climate.

RUSSELL: One of the most uncertain aspects of predicting climate to this day is how we represent clouds and precipitation in global models.

LACAPRA: But before the effects of airborne bacteria can be included in climate models, Russell says we're going to need to know a lot more about them. Nenes and Konstantinidis agree their current study raises as many questions as it answers. Their research is published in the Proceedings of the National Academy of Sciences.

Veronique LaCapra, NPR News

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