Look, up in the sky! It's a bird! It's a plane! No, it's a flying bacterium! Don't scoff--scientists have known for years that bacteria are floating around in the atmosphere. Now researchers report that microbes also feed and breed while they're up in the clouds, raising the possibility that airborne bacteria influence atmospheric chemistry.
Almost no earthly environment is out of bounds for bacteria, including the atmosphere. And while the clouds aren't exactly teeming with life, air-sampling instruments have trapped bacteria more than 11 kilometers above sea level. Carried aloft by rising currents, some microbes can also drift thousands of kilometers before landing. But scientists thought that, like many long-distance travelers, the bugs were inert during their time in the air.
To test whether atmospheric bacteria were inactive, limnologist Birgit Sattler of the University of Innsbruck, Austria, and colleagues collected cloud water from a site 3100 meters up in the Austrian Alps. They kept the samples frozen and analyzed them back in the lab. Once thawed, the cloud bacteria released carbon and slurped up radioactively labeled amino acids and thymidine, an ingredient of DNA, showing that they were metabolizing and reproducing even when on the verge of freezing. That bacteria straight from clouds were active suggests that cloudborne bacteria are as well, the researchers conclude in the 15 January issue of Geophysical Research Letters.
Sattler says it's possible that these bugs affect pollution or chemical reactions in the atmosphere. But the researchers haven't cinched their case that bacteria are active in clouds, says microbiologist Bruce Lighthart of the Microbial Aerosol Research Laboratory in Monmouth, Oregon. The measurements show bacteria have the potential to reproduce while aloft, he says, but actually catching the bugs in the act will be tricky.
Limnology Division at the University of Innsbruck