Partitioning of microbial cells between clouds and precipitation

It is known that microorganisms are present in the outdoor atmosphere, in clouds and precipitation. These microorganisms originate from various local and distant sources and consist of very diverse and ephemeral communities. The most abundant bacterial taxa typically include Alpha-, Betaand Gamma-Proteobacteria, with notably Pseudomonas and Sphingomonas among the dominant genera observed. Still, very little is known about their sources, metabolic activity, distribution, and their dynamics during their atmospheric life cycle. It was proposed in the past that bacteria with high ice nucleation activity are likely more efficiently precipitated than others [1]. Here, we extend this hypothesis and suggest more generally that different bacteria taxa could exhibit different phase partitioning between aerosol particles, cloud and rainwater, which may affect their atmospheric residence times. This implies that microorganisms are not equally distributed among the different atmospheric compartments (clouds, aerosols and precipitation).