AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Hygroscopicity and Cloud Condensation Nuclei Activity of Bacterial Cells
Natasha DeLeon-Rodriguez, Aikaterini Bougiatioti, Nimmy Mathew, Arnaldo Negron-Marty, Sara Purdue, Samantha Waters, Michael Bergin, Konstantinos Konstantinidis, ATHANASIOS NENES, Georgia Institute of Technology
Abstract Number: 446 Working Group: Bioaerosols
Abstract The abundance of bacterial cells in the atmosphere can reach relatively high numbers, but more rigorous research is needed to investigate the extent to which they play a role in atmospheric chemistry, cloud formation, and precipitation. It has been known for decades that bacteria are among the most efficient ice nuclei in the atmosphere, and there have been several immersion freezing studies of various bacterial isolates. However, the ability of bacteria to initiate cloud droplet formation remains poorly characterized. There are a few existing studies that have measured the cloud condensation nuclei (CCN) activity of different bacteria, but the underlying mechanism(s) of this activity, how it is related to bacterial cell hygroscopicity, and the physiological state of the cell, remain unknown. The objective of this study was to determine whether the affinity of different bacterial cells to water might be related to CCN activity. To this end, we collected samples from rainwater and ambient air at different locations (urban cities and rain forest) and altitudes (~10 km and surface air). Over 20 bacterial isolates were obtained from these samples using different minimal and rich media, and were identified based on sequencing of the 16S rRNA gene. The hydrophobicity of different bacterial cell lawns was evaluated by contact angle measurements with water. A wide range of contact angles was observed among our isolates, ranging from very hydrophilic to very hydrophobic; the majority of the isolates, however, were found to be hydrophilic. The CCN activity of each isolate was studied by introducing aerosolized bacteria into a continuous flow stream-wise thermal gradient CCN counter. These data show that the hydrophilic bacteria used here have a critical supersaturation of 0.06% compared to the hydrophobic bacteria, which had a critical supersaturation of 0.15% or higher. These supersaturation conditions are relevant for certain areas of the planet, indicating the potential of hydrophilic bacteria to influence cloud formation and precipitation in these regions.