Via Maggie Koerth-Baker I learned something quite surprising, that there exists a type of bacteria called Pseudomonas syringae that causes disease in plants but can also help turn cold water rapidly into ice. And by rapidly, I mean really rapidly, in seconds. Watch what happens as the bacteria are inserted into a bottle of cold water.
Koerth-Baker explains what is going on.
P. syringae gets this skill from the proteins that cover its surface membrane. The proteins basically form a physical structure that water molecules latch onto. That structure also orients the molecules in a way that prompts the formation of ice crystals. It’s these proteins that really serve as the instigator of ice nucleation and they’re incredibly efficient at it — far more so than dust. That means that P. syringae can get water to freeze at higher temperatures than would happen without its help. Pure water won’t crystallize until temperatures dip down to -40 degrees F. If the water in our atmosphere were pure, most of us would have never seen snow. Add in the proteins from P. syringae, though, and, suddenly, ice can form at 27 degrees F. You can even get ice formation at higher temperatures than that, depending on the specific strain of P. syringae involved, and how densely the ice-forming proteins are packed along its surface.
Commercial snow machines use the proteins (though not the bacteria itself) to help instigate the creation of snow on ski mountains. In other words, you can thank P. syringae for all the snowboarding and downhill ski action the Winter Olympics.
It is surprising the new things one learns about familiar phenomena.