Bacteria in the atmosphere - another extreme environment?

A group out of Denmark recently did biochemical and bacteriological analysis of hailstones. A quick glance at some neat things in here: 

• bacteria found at a density of ~2000 cells/ml. That's not very high compared to soil at ~10,000,000 cells/g, but hey, this is in a hailstone! 
• Single cloud droplets however are not individually very poluation. The researchers estimate that 1 in 1,000,000 storm cloud droplets have a a bacterial cell in them. 
• this paper also touches on the carbon sources and how that may relate to the bacteria

Realize that there are a lot of bacteria hanging out in the atmosphere. There's been a lot of work on this recently, and some of it suggests that these bacteria are metabolically active while up there. There is also research that suggests that these bacteria can act as nucleation points for condensation. I like another statement that is made in this paper that considers the atmosphere as yet another one of our "extreme environments"  - another model for life on other planets perhaps? 


Šantl-Temkiv et al. 2013 Hailstones: A Window into the Microbial and Chemical Inventory of a Storm Cloud. PLOS 



http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053550