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. 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. 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.

中文翻译：

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从大气中掉落的细菌群落

排放到大气中的细菌最终通过沉降（干沉降）或降水（湿沉降）沉降到土壤圈，构成了地球上物质循环的一部分，包括水循环。在这项研究中，我们旨在研究细菌沉积的分类学组成和通量密度，但对于每种大气沉积模式的相对贡献，分类学结构和成员以及大气中的空气动力学特性了解甚少。人们发现，降水是大气细菌沉积的主要因素，占我们韩国采样点总通量密度的95％，而降水中的细菌群落在结构和成员方面与沉积中的细菌群落明显不同。观察到大气细菌的空气动力学直径较大，年平均为8.84μm，这似乎与它们较大的沉降速度有关，所有细菌类群的年平均为1.72 cm s-1。观测到的大气细菌的平均沉降速度大于以前报道的真菌和植物的平均沉降速度。大气细菌的大空气动力学直径很可能是由于聚集和/或附着在其他较大颗粒上引起的，它们被认为有助于大的沉积速度，作为云核的高效率以及大气细菌的大量沉淀。此外，沉淀和沉积之间的不同微生物群可能表明特定的细菌参与和/或云中细菌的选择性生长。