P. syringae is one of 78 species within the genus Pseudomonas and there are a whopping 50 different strains of P. syringae, each one infecting a different plant species. It was first described way back in 1902 and has become a model organism for plant-pathogen interactions. It is a Gram-negative, rod-shaped, obligate aerobe with polar flagella - essentially, it looks just like E. coli. P. syringae loves cool, wet environments within the “phyllosphere” - the above-ground portions of plants - where it colonizes the leaf surfaces of plants like tomatoes, rice, beans, and tobacco.
Many strains of P. syringae secrete toxins and enzymes that degrade the plant cell walls. One toxin, syringomycin, acts like a detergent at high concentrations to dissolve the cell walls. Syringomycin can also aggregate to form pores in the plant cells, releasing nutrients that are likely utilized by the bacteria.
My favorite thing, without a doubt, about P. syringae is that it nucleates ice crystal and water droplet formation. These bacteria produce Ina (“ice nucleation active”) proteins that sit on the bacterial cell surface and position water molecules so they can easily form ice crystals at temperatures just below the freezing point. There are actually so many P. syringae cells on the average leaf that they are largely responsible for damaging frost formation. While this is bad news for farmers, it’s great news for ski resorts that actually use Ina proteins to make artificial snow!
Last, but not least, I’ll leave you with this Science Friday clip all about ice-nucleating bacteria...
Sources: MicrobeWiki, Wikipedia, Science Friday