Spatio-temporal variability of airborne bacterial communities and their correlation with particulate matter chemical composition across two urban areas

Abstract

The study of spatio-temporal variability of airborne bacterial communities has recently gained importance due to the evidence that airborne bacteria are involved in atmospheric processes and can affect human health. In this work, we described the structure of airborne microbial communities in two urban areas (Milan and Venice, Northern Italy) through the sequencing, by the Illumina platform, of libraries containing the V5-V6 hypervariable regions of the 16S rRNA gene and estimated the abundance of airborne bacteria with quantitative PCR (qPCR). Airborne microbial communities were dominated by few taxa, particularly Burkholderiales and Actinomycetales, more abundant in colder seasons, and Chloroplasts, more abundant in warmer seasons. By partitioning the variation in bacterial community structure, we could assess that environmental and meteorological conditions, including variability between cities and seasons, were the major determinants of the observed variation in bacterial community structure, while chemical composition of atmospheric particulate matter (PM) had a minor contribution. Particularly, Ba, SO4 (2-) and Mg(2+) concentrations were significantly correlated with microbial community structure, but it was not possible to assess whether they simply co-varied with seasonal shifts of bacterial inputs to the atmosphere, or their variation favoured specific taxa. Both local sources of bacteria and atmospheric dispersal were involved in the assembling of airborne microbial communities, as suggested, to the one side by the large abundance of bacteria typical of lagoon environments (Rhodobacterales) observed in spring air samples from Venice and to the other by the significant effect of wind speed in shaping airborne bacterial communities at all sites.

Spatiotemporal Controls on the Urban Aerobiome

“…As indicated by our conceptual model (Figure 8), our study encompassed multiple processes occurring across a range of days to months that could be expected to impact the aerobiome. In particular, seasonal biotic processes (e.g., vegetation senescence), changes in weather and prevailing winds, and regional-scale human activities (e.g., agriculture) appeared to play roles in the observed shifts in dominant taxonomic groups, as has been noted in other studies (Gandolfi et al, 2015;Lee et al, 2017).…”

Molecular Evidence for Metabolically Active Bacteria in the Atmosphere

“…Our rDNA-based bacterial community data is consistent with prior studies and includes several taxonomic orders commonly found in air samples. For example, the Actinomycetales, which were abundant in our samples, are frequently found in the atmosphere ( Brodie et al, 2007 ; Bowers et al, 2013 ; Gandolfi et al, 2015 ) and have been found to be abundant in other studies at high elevation sites ( Bowers et al, 2012 ), including MBO ( Smith et al, 2013 ). There are two reasons to expect this order to be abundant in the atmosphere.…”

The Relationship between Air-Mass Trajectories and the Abundance of Dust-Borne Prokaryotes at the SE Mediterranean Sea

“…The variability in the prokaryotic cell abundances may be attributed to the distance from nearby shore/land [12], the atmospheric route (i.e., height, duration), the concentration of dust/aerosol, as well as to differences in methodology of aerosol collection and procedure for assessing cell numbers (i.e., microscopy, qPCR, culture-based methods) [12,33,35]. Further, different meteorological conditions such as wind speed, humidity, and atmospheric pH may also affect airborne microbial community structure [36,37].…”