At temperatures above -39°C, the freezing of supercooled water requires the presence of particles, known as ice nucleating particles (INPs). Their chemical composition and structure determine the temperature of freezing. It is generally assumed that mineral particles only nucleate ice below -10°C, whereas certain biological particles can induce freezing at temperatures as low as -2°C. In bacteria, ice nucleation has been associated with pathogenicity: it contributes to damaging plant structures. In the plant pathogenic bacteria Pseudomonas syringae, the most active and best characterized biological ice nucleator in nature, the ability to induce freezing is linked to a membrane protein whose structure is very similar to that of antifreeze proteins, but which is much larger in size; this protein acts as a matrix for the organization of water molecules into a crystal embryo which, at sub-zero temperatures, grows spontaneously. The life cycle of ice nucleation active bacteria and the maintenance during evolution of such demanding function could be intimately linked with atmospheric transport. In the atmosphere, the formation of ice in clouds has a direct impact on the Earth's radiation balance and also triggers precipitation as a result of well-known physical processes (Bergeron-Findeisen and Hallett Mossop). A theory called 'bioprecipitation' establishes a positive feedback between vegetation, epiphytic bacteria and precipitation: vegetation emits ice-nucleating bacteria which, once in the air and clouds, trigger precipitation and are deposited again on the vegetation cover with the precipitation, promoting the growth of plants and epiphytic bacteria. During this conference, I will introduce current knowledge about ice nucleation active bacteria and proteins, their occurrence in the phyllosphere and in the atmosphere, and hints towards the existence of bioprecipitation.