Falling bacterial communities from the atmosphere
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(2020) 15:22
Environmental Microbiome
RESEARCH ARTICLE
Open Access
Falling bacterial communities from the atmosphere Cheolwoon Woo1 and Naomichi Yamamoto1,2*
Abstract Background: Bacteria emitted into the atmosphere eventually settle to the pedosphere via sedimentation (dry deposition) or precipitation (wet deposition), constituting a part of the global cycling of substances on Earth, including the water cycle. In this study, we aim to investigate the taxonomic compositions and flux densities of bacterial deposition, for which little is known regarding the relative contributions of each mode of atmospheric deposition, the taxonomic structures and memberships, and the aerodynamic properties in the atmosphere. Results: Precipitation was found to dominate atmospheric bacterial deposition, contributing to 95% of the total flux density at our sampling site in Korea, while bacterial communities in precipitation were significantly different from those in sedimentation, in terms of both their structures and memberships. Large aerodynamic diameters of atmospheric bacteria were observed, with an annual mean of 8.84 μm, which appears to be related to their large sedimentation velocities, with an annual mean of 1.72 cm s− 1 for all bacterial taxa combined. The observed mean sedimentation velocity for atmospheric bacteria was larger than the previously reported mean sedimentation velocities for fungi and plants. Conclusions: Large aerodynamic diameters of atmospheric bacteria, which are likely due to the aggregation and/or attachment to other larger particles, are thought to contribute to large sedimentation velocities, high efficiencies as cloud nuclei, and large amounts of precipitation of atmospheric bacteria. Moreover, the different microbiotas between precipitation and sedimentation might indicate specific bacterial involvement and/or selective bacterial growth in clouds. Overall, our findings add novel insight into how bacteria participate in atmospheric processes and material circulations, including hydrological circulation, on Earth. Keywords: Bioprecipitation, Biosedimentation, Bioaerosols, 16S rRNA gene, Aerobiology, Aero-microbiology
Background Bacteria are ubiquitous in the lithosphere [1], hydrosphere [2], and atmosphere [3, 4]. Although the number of bacterial species is still not accurately known, a study [5] reported 0.8–1.6 million operational taxonomic units (OTUs) based on sequences of the V4 region of the 16S rRNA gene at a 97% sequence similarity threshold. Bacteria are emitted into the atmosphere with estimated * Correspondence: [email protected] 1 Department of Environmental Health Sciences, Graduate School of Public Health, Seoul National University, Seoul 08826, Republic of Korea 2 Institute of Health and Environment, Seoul National University, Seoul 08826, Republic of Korea
global rates of 0.7–28.1 Tg y− 1 [6]. The emitted bacteria play roles in ecological and climate systems, for example, by acting as cloud condensation nuclei and/or iceforming nuclei [6–8]. Moreover, the emitted bacteria eve
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