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Summary: Airborne bacteria are abundant and can vary with land use. Urban expansion is increasing rapidly at a global scale, altering natural sources of airborne bacterial biodiversity, as soils and native plants are replaced by pavement and managed yards. Urbanization homogenizes the biodiversity of larger organisms, but its effects are understudied with respect to microbes. This study uses categorical and gradient approaches to examine airborne bacterial communities in southwest Michigan (USA). Airborne communities carried a gut‐microbial signature and were equally homogenous above urban and rural sites, despite greater homogeneity of soil communities at urban sites. Ruminococcaceae were abundant, the source of which is likely wildlife. Beyond the gut‐microbial signature, there were underlying effects of land use, which were evident in the shared airborne taxa across urban and rural sites. Bacillales, Burkholderiales, Alteromonadales and Pseudomonadales were shared more across urban sites, while Xanthomonadales, which contains crop‐plant pathogens, were shared across rural agricultural sites. These results suggest that taxa which may distribute globally, coupled with localized sources, contribute to urban communities, while regional rural activities drive rural composition. We determined that soils were unlikely to contribute to broad distribution of some plant‐associated taxa, but may be a source for distribution of others. [ABSTRACT FROM AUTHOR]

Land use influences the composition of near-surface airborne bacterial communities, and bacteria can be transported through the atmosphere at global scales. The atmosphere mixes vertically, but rigorously assessing whether the effects of land use on atmospheric communities extends to higher altitudes requires examining communities from multiple altitudes collected at a stable location and timeframe. In this study, we collected near-surface (<2 m) and higher-altitude (150 m) air samples from three sites in an agricultural/developed location and a forested/undeveloped location. We used bacterial 16S rRNA amplicon sequencing to compare communities and predict functionality by altitude. Higher-altitude and near-surface communities did not differ in composition within each location. Communities collected above the undeveloped location were equally variable at both altitudes; higher-altitude samples from the developed location predominantly contained Firmicutes and were less variable than near-surface samples. We also compared airborne taxa to those present in soil and snow. Communities from higher-altitude samples above the developed location contained fewer overlapping taxa with soil and snow sources, and overlapping Operational Taxonomic Units (OTUs) among the three sources differed by location. Our results suggest that land use affects the composition of both near-surface and higher-altitude airborne bacterial communities and, therefore, may influence broad bacterial dispersal patterns. This small-scale pilot study provides a framework for simultaneously examining local and regional airborne microbial communities that can be applied to larger studies or studies using different types of samplers. [ABSTRACT FROM AUTHOR]