Pseudomonas syringae is a pretty nasty plant pathogen. In fact, a lot of my reading for my project involves inhibiting or otherwise deterring it from infecting plants. But even a common disease causer like this can have its uses!
Because bacteria are so tiny, they can interact with things much smaller than we can. For example; water! Clouds are full of bacteria (see this blog post for more details) condensing water vapour together, but that's not all they can do. P. syringae can freeze water! Only a few degrees above normal freezing point, but a few degrees can make a huge difference (just look at the climate change stats!). This cool paper shows how they do it; they use proteins to move the water into structured arrangements which encourages freezing.