Abstract
Abstract. The residence time of bacterial cells in the atmosphere is predictable by numerical models. However, estimations of their aerial dispersion as living entities are limited by a lack of information concerning survival rates and behavior in relation to atmospheric water. Here we investigate the viability and ice nucleation (IN) activity of typical atmospheric ice nucleation active bacteria (Pseudomonas syringae and P. fluorescens) when airborne in a cloud simulation chamber (AIDA, Karlsruhe, Germany). Cell suspensions were sprayed into the chamber and aerosol samples were collected by impingement at designated times over a total duration of up to 18 h, and at some occasions after dissipation of a cloud formed by depressurization. Aerosol concentration was monitored simultaneously by online instruments. The cultivability of airborne cells decreased exponentially over time with a half-life time of 250 ± 30 min (about 3.5 to 4.5 h). In contrast, IN activity remained unchanged for several hours after aerosolization, demonstrating that IN activity was maintained after cell death. Interestingly, the relative abundance of IN active cells still airborne in the chamber was strongly decreased after cloud formation and dissipation. This illustrates the preferential precipitation of IN active cells by wet processes. Our results indicate that from 106 cells aerosolized from a surface, one would survive the average duration of its atmospheric journey estimated at 3.4 days. Statistically, this corresponds to the emission of 1 cell that achieves dissemination every ~ 33 min m−2 of cultivated crops fields, a strong source of airborne bacteria. Based on the observed survival rates, depending on wind speed, the trajectory endpoint could be situated several hundreds to thousands of kilometers from the emission source. These results should improve the representation of the aerial dissemination of bacteria in numeric models.
Highlights
Microorganisms are known to be dispersed into the atmosphere and disseminated over long distances (e.g., Bovallius et al, 1978; Brodie et al, 2007; Griffin et al, 2001; Smith et al, 2013, and review by Morris et al, 2013)
CellsIMP was significantly higher than CellsAPS by a factor of 1.82 ± 0.40 in average (t test; p < 0.01; n = 13), indicating the presence of cell aggregates in the ∼ 1 μm aerosol population
For bacteria, aerial dissemination is clearly a compromise between the distance traveled and the chances of successful dissemination
Summary
Microorganisms are known to be dispersed into the atmosphere and disseminated over long distances (e.g., Bovallius et al, 1978; Brodie et al, 2007; Griffin et al, 2001; Smith et al, 2013, and review by Morris et al, 2013). Burrows et al (2009a, b) constrained a general atmospheric circulation model using data from the literature and estimates of concentrations and vertical fluxes of airborne microorganisms They estimated that ∼ 1024 bacteria are emitted into the atmosphere each year at the global scale, with a residence time aloft between 2 and 10 days (∼ 3 days on average) depending on emission sources and on meteorological conditions. Such a time span should allow microbial cells (i.e. particles of ∼ 1 μm) to travel over hundreds or thousands of kilometers. It is not clear what fraction of the aerosolized microorganisms survive over this timescale, and if they maintain properties allowing interactions with atmospheric water
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