Abstract
Abstract. A next-generation sequencing (NGS)-based taxonomic analysis was carried out on airborne bacteria sampled at ground level in two periods (May and September) and two opposite locations on the north–south axis of the island of Sardinia. Located in a central position of the Mediterranean basin, Sardinia constitutes a suitable outpost for revealing possible immigration of bacterial taxa during transcontinental particle discharge between Africa and Europe. With the aim of verifying relative effects of dust outbreaks, sampling period, and sampling site on the airborne bacterial community composition, we compared air collected during dust-carrying meteorological events to that coming from wind regimes not associated with long-distance particle lifting. Results indicated that (a) higher microbial diversity and richness (118 vs. 65 orders) and increased community evenness were observed in the campaign carried out in September in comparison to the one in May, irrespective of the place of collection and of the presence or absence of dust outbreaks; (b) during the period of standard wind regimes without transcontinental outbreaks, a synchronous concerted turnover of bacterial communities across distant locations of the same island, accompanied as mentioned by a parallel rise in bacterial diversity and community evenness, appears to have occurred; (c) changes in wind provenance could transiently change community composition in the locality placed on the coast facing the incoming wind but not in the one located at the opposite side of the island, and for this reason the community changes brought from dust outbreaks of African origin are observed only in the sampling station exposed to the south; (d) the same winds, once proceeding over land, appear to uplift bacteria belonging to a common core already present over the region, which dilute or replace those that were associated with the air coming from the sea or conveyed by the dust particulates, explaining the two prior points; and (e) the hierarchy of the variables tested in determining bacterial assemblages composition results is as follows: sampling period≫ongoing meteorological events>sampling location within the island.
Highlights
With a total volume evaluated of 4.5 × 1018 m3, the terrestrial lower atmosphere represents the most extended potential biome, followed by water, 1.3 × 1018 m3 (Gleick, 1993), and by soil with 6.2 × 1016 m3
With the aim of verifying relative effects of dust outbreaks, sampling period, and sampling site on the airborne bacterial community composition, we compared air collected during dustcarrying meteorological events to that coming from wind regimes not associated with long-distance particle lifting
In a prior study (Rosselli et al, 2015), we described a core microbiome in the bacteria cast upon the island of Sardinia under different wind regimes through analyses of DNA from deposited particles
Summary
With a total volume evaluated of 4.5 × 1018 m3, the terrestrial lower atmosphere represents the most extended potential biome, followed by water, 1.3 × 1018 m3 (Gleick, 1993), and by soil with 6.2 × 1016 m3 Concerning atmosphere, microbial cells and propagules embody a suitable conformation to take advantage of air utilization as an environment for survival and dispersal. Their movement can be favored by a natural mobile reservoir of physical solid carriers represented by the air-dispersed particulate matter. Such particles range between 0.2 and 100 μm in size (Bernstein et al, 2004; Ryder et al, 2018) and average loads of 1–100 μg m−3 (Williams et al, 2002; Van Dingenen et al, 2004). It has been estimated that more than 5000 Tg of sea salt (Tegen et al, 1997) and 1000–2000 Tg of soil particles, passively uplifting and transporting live cells, are released every year in the atmosphere giving rise to a widely heterogeneous material conveyed from different sources (Guang et al, 2004; McTainsh, 1989; Knippertz et al, 2009)
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