Louis Pasteur opened a glass flask on Montanvert Glacier in the French Alps in 1860 and collected some air. A few days later the bottom of that flask was teeming with goo—proof to Pasteur and his colleagues that there was something in the air, something invisible but quite real. Today we understand what that invisible stuff is—microbes aloft in our atmosphere—but despite the more than 150 years that have passed since Pasteur's experiment, scientists are just beginning to understand how microorganisms in the air affect life on earth.

Recently scientists captured more than 2,100 species of microbes traversing the Pacific Ocean from Asia to North America on huge plumes of air in the upper troposphere—up to 12 miles above the surface of the earth. A good fraction of them were bacteria, which can mean trouble for human health. In Africa, in a region known as the meningitis belt, dust storms carry the bacterium Neisseria meningitidis (pictured above), which infects around 200,000 people there annually. Yet for most people in most places, the microbes in the air are totally harmless, says David Smith, a microbiologist at the nasa Kennedy Space Center and lead author on the work that found the 2,100 traveling microbes. “You don't need to be worried,” says Smith, whose findings were published online last December in the journal Applied and Environmental Microbiology. “This has been happening naturally, always.”

Beyond health, microbes in the atmosphere might also be important for climate. “We're interested in whether they can contribute appreciably to the concentrations of cloud nuclei,” says Susannah Burrows, an atmospheric scientist at Pacific Northwest National Laboratory in Richland, Wash. Bacteria can clump together, forming the seed around which clouds form and thus providing a key component of our atmosphere, she notes.

Other researchers wonder exactly how microbes behave while aloft and if they can reproduce as they travel. “We have several indications that microbes in the air are alive and active” and not just hitching a ride, says Paraskevi Polymenakou, an atmospheric microbiologist at the Hellenic Center for Marine Research in Greece.

For Dale Griffin, a microbiologist at the U.S. Geological Survey, the questions push beyond the atmosphere. “No matter how high we look, we seem to be able to find life,” he says. Smith wonders not just how high that life goes but how it survives at such heights. “As a student in biology, I felt like everything had already been investigated,” he says. “The atmosphere allows the opportunity to characterize a place where nobody has looked for life.

This article was originally published with the title Up with Microbes.

1 Comments

1. 1. Steven 04:24 PM 3/1/13

   Pseudomonas syringae bacteria make a protein which causes water to freeze at higher temperatures, so frost will damage the plants they are on and plant nutrients will be released for bacterial growth and propagation.
   Many of these bacteria are present in clouds and nucleate ice particles which develop into snowflakes or rain in warmer climates.
   The protein is much more effective at nucleating water droplets than dust or soot particles.
   There has been quite a bit of work identifying bacterial in clouds and their effect on rainfall, and even in cloud seeding with bacteria, since it would be a lot more effective than using chemicals or particles.
   Possibly rainfall could be enhanced, and even enhanced cloud formation to counter some of the effects of global warming.
   One of the problems is however that if there is any flood or water damage from the rainfall, then the people doing the cloud seeding are liable for damages induced by their cloud seeing, so probably we won't see any cloud seeding, even as droughts worsen and there are widespread crop failures.
   While scientific advances in this area are possible, it's not likely to occur due to legal liability issues.

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