Archive
2014
January
February
March
April
May
June
July
August
September
October
November
December
2013
January
February
March
April
May
June
July
August
September
October
November
December
2012
January
February
March
April
May
June
July
August
September
October
November
December
2011
January
February
March
April
May
June
July
August
September
October
November
December
2010
January
February
March
April
May
June
July
August
September
October
November
December
2009
January
February
March
April
May
June
July
August
September
October
November
December
2008
January
February
March
April
May
June
July
August
September
October
November
December
2007
January
February
March
April
May
June
July
August
September
October
November
December
2006
March
April
May
June
July
August
September
October
November
December
Jan. 25, 2013

Cloudy With a Chance of Bacteria

by Charles Bergquist

Click to enlarge images
Germophobes, beware—that cloud on the horizon contains more than just rain. The atmosphere is filled with airborne bacteria, and a new study finds that even in the harsh conditions inside a storm cloud, some bacteria manage to survive—and may even reproduce and grow. “Storm clouds are among the most extreme habitats on earth where microbial life exists,” says Tina Santl-Temkiv, a postdoc at Aarhus University in Denmark and one of the authors of a paper published in the journal PLOS One
 
Santl-Temkiv and colleagues sampled the insides of a storm cloud by collecting hailstones, scooped from the ground in sterile bags within five minutes of a 2009 storm. The team was interested in airborne bacteria, and a serendipitous phone call set this experiment in motion. “It was by pure chance that this happened,” says Santl-Temkiv. “I was talking on the phone to a friend from Slovenia while the storm happened, so I asked him to go out and collect the hailstones for me.” The friend’s speedy work preserved the large icy spheres, each around 3-5 cm in diameter, as frozen time capsules of cloud conditions.
 
Only about one in every million tiny cloud droplets contains a bacterial cell, according to the researchers. When lots of those droplets coalesce into a hailstone, however, that can add up to thousands of bacterial cells per milliliter of liquid. The researchers found many species of bacteria in the hailstones, as well as big differences in bacterial communities from one stone to another. But the majority of species were varieties normally found either in soil or on plants, swept into the skies from the ground. Dissolved organic material from soil particles carried in the air can provide nutrients for the bacteria to live on while aloft.
 
When the researchers tried to cultivate the bacteria they recovered, they learned that strains normally associated with plants had an edge in viability. “Bacteria that grow on plant surfaces have to deal with extreme conditions such as dryness, high UV-radiation, and large variations in temperature,” says Santl-Temkiv. “Being adapted to these stressful conditions can help plant-surface bacteria to survive and remain active in the atmosphere.” While bacteria need liquid to be active, the plant-surface bacteria may even be able to persist after a cloud dissipates, floating freely in the air until they find a new liquid home, she says.
 
So are blue-sky days less bacteria-ridden than cloudy days? Not necessarily. “The numbers of bacteria getting from their ground environments into the air depends on the weather conditions,” says Santl-Temkiv. “It may well happen that on a sunny day the surface air gets heated and starts rising, bringing with it bacteria from the ground. As a consequence, there may be a larger number of bacteria ending up in the atmosphere.” 
About Charles Bergquist

Charles reminds Ira when it's time to stop talking, helps wrangle this Web site, and produces segments for the radio program. His favorite stories involve chemistry, inventions, nanotechnology, and shiny things with blinking lights.

The views expressed are those of the author and are not necessarily those of Science Friday.

Science Friday® is produced by the Science Friday Initiative, a 501(c)(3) nonprofit organization.

Science Friday® and SciFri® are registered service marks of Science Friday, Inc. Site design by Pentagram; engineering by Mediapolis.

 

topics