Evolution in the Clouds
The recipe for making rain in clouds involves something that will help freeze molecules of water at a higher than normal temperature. In turns out that something is a kind of bacteria. Scientists are trying to figure out why the bacteria has a unique ability to make rain. I’m Jim Metzner and this is the Pulse of the Planet.
Boris Vinatzer is an Associate Professor of Plant Pathology who’s been studying pseudomonas syringae the bacteria that can ice-nucleate water turn molecules of water in crystals of ice , the first step in making rain.
Vinatzer: Why did bacteria evolve the ability to freeze water to nucleate ice at relatively high temperatures? One hypothesis is that when the bacteria move up in the atmosphere; they end up in clouds. But clouds are a harsh environment. It would be to the advantage of bacteria to come back down to earth. So some of us think that pseudomonas syringae and other bacteria may have evolved so that then they nucleate the water around them, they become heavier with the ice crystal around them and that that helps them to come back down to earth and start growing again on plants.
Why would bacteria go up into clouds? It’s a harsh environment up there; very cold; there’s UV, a lot of very strong UV radiation. One advantage for bacteria to go up in the atmosphere would be dispersal. One bacterium grows very well on a plant; but would always be stuck in that one field and would not be very successful. If this bacterium evolves the ability to move long distance in clouds, and then fall down somewhere else on earth, and then grow there, that would be a great selective advantage for this bacteria.
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