Our clouds are full of bacteria

Researchers from the Georgia Institute of Technology and NASA have been sampling the air in the upper troposphere (extending up to between 7 and 20 km, depending on the location and time of year). And what did they find? Lots and lots of bacteria.

We knew that clouds weren’t composed solely of water molecules. For one thing, storms often kick dust and debris up into the sky. As I’ve previously written, these particles can traverse the world before raining back down on Earth. For another, the very formation of clouds sometimes requires nucleation centers to start the water molecules freezing. Inorganic dust works well for this purpose, but some types of bacteria might be even better. After all, some plant pathogens work by serving as nucleation centers in leaves; the resultant freeze of the plant tissues damages them enough to allow the bacteria to enter.

The scientists took the air samples at various altitudes around the country both during and after hurricanes. I don’t envy the person whose job it was to fly an airplane through a hurricane and collect a cup of air. In any case, the scientists found that about 20% of the microscopic particulates were in fact bacterial cells. Even more intriguingly, most of the bacteria even at the highest elevations were alive. 

Not surprisingly, hurricanes tend to alter the composition of the microbial communities quite a bit. It was only during hurricanes that bacteria associated with human or animal feces appeared in the samples, as good a reason as any not to go outside during a hurricane.

For more on this, see Ed Yong's post at Not Exactly Rocket Science.

DeLeon-Rodriguez, N., Lathem, T., Rodriguez-R, L., Barazesh, J., Anderson, B., Beyersdorf, A., Ziemba, L., Bergin, M., Nenes, A., & Konstantinidis, K. (2013). Microbiome of the upper troposphere: Species composition and prevalence, effects of tropical storms, and atmospheric implications Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1212089110.