Ice nucleation active bacteria and their potential role in precipitation

Certain bacteria that are commonly found on plants have the capacity to catalyze the freezing of Supercooled water at temperatures as warm as -1degreesC. This is conferred by a protein in the outer membrane of the bacterial cell. Because of the abundance of these bacteria and the warm temperature at which they function as ice nuclei, they are considered to be among the most active of the naturally-occuring ice nuclei. As plant pathogens, antagonists of plain pathogens and as causal agents of frost damage, these bacteria have well-studied interactions with plants. Here we propose that these bacteria also play a role in atmospheric processes leading to rain, given that they are readily disseminated into the atmosphere and have been found in clouds at altitudes of several kilometers. That they participate in a sort of biological cycle of precipitation - whereby they are transported into clouds from plant canopies and incite rain thereby causing favorable conditions for their growth on plant surfaces - was proposed about 20 years ago. Today, sufficient evidence and meteorological tools have emerged to re-ignite interest in bioprecipitation and in the ways in which plants play a role as cloud seeders.