http://judson.blogs.nytimes.com/2008/02/19/when-life-goes-cloudy/index.html

But the paper in “Geophysical Research Letters” went further. It claimed not just that microbes are traveling via cloud, but that some of them are actually living there — growing, metabolizing, reproducing — until plummeting back to earth when the cloud rains.

Clouds are much more like tide pools than they are like Arctic lakes. A microbe arriving in a cloud from the ground might experience a drop in temperature from, say, 15C (59F) to -20C (-4F) in a few hours. Worse, as a cloud forms, the osmotic pressure — caused by the difference in conditions between the inside of the cell and the outside — fluctuates wildly. At the same time, the droplets that constitute clouds condense and evaporate rapidly and continuously, and sometimes they freeze. Then, when it rains, the microbes return to Earth, and must be able to survive there, too. So who are the cloud dwellers, and what do they live on?

Thanks to Steve Bellberby