Size-Resolved Community Structure of Bacteria and Fungi Transported by Dust in the Middle East.

Daniella Gat,Yinon Rudich,Naama Reicher,Bethany V Wyld,Ralf Zimmermann,Matan Alayof,Mark D Tarn,Shai Schechter

doi:10.3389/fmicb.2021.744117

Abstract

The atmosphere plays an important role in transporting microorganisms on a global scale, yet the processes affecting the composition of the airborne microbiome, the aerobiome, are not fully outlined. Here we present the community compositions of bacteria and fungi obtained by DNA amplicon-sequencing of aerosol samples collected in a size-resolved manner during nine consecutive days in central Israel. The campaign captured dust events originating from the Sahara and the Arabian deserts, as well as days without dust (“clear days”). We found that the source of the aerosol was the main variable contributing to the composition of both fungal and bacterial communities. Significant differences were also observed between communities representing particles of different sizes. We show evidence for the significant transport of bacteria as cell-aggregates and/or via bacterial attachment to particles during dust events. Our findings further point to the mixing of local and transported bacterial communities, observed mostly in particles smaller than 0.6 μm in diameter, representing bacterial single cells. Fungal communities showed the highest dependence on the source of the aerosols, along with significant daily variability, and without significant mixing between sources, possibly due to their larger aerodynamic size and shorter atmospheric residence times. These results, obtained under highly varied atmospheric conditions, provide significant assurances to previously raised hypotheses and could set the course for future studies on aerobiome composition.

Highlights

Desert dust storms have been identified as a significant source for microorganisms in the atmosphere, estimated to emit 700–1,400 Gg of bacteria-carrying particles into the atmosphere per year (Griffin et al, 2006; Griffin, 2007; Burrows et al, 2009a)
Our results show that microbial communities associated with fine particles of D50 < 0.6 μm were less affected by the source of the air-mass and showed greater withingroup similarity than those associated with coarse particles, as observed by the average Euclidean distances between samples of different sources within a single size-class (Figure 2) and by Analysis of molecular variance (AMOVA) tests (Supplementary Table 3)
This study provides further evidence in support of previous suggestions regarding the mode of transport of microorganisms in the atmosphere, and to the parameters affecting the composition of the aerobiome in the East Mediterranean

Summary

Introduction

Desert dust storms have been identified as a significant source for microorganisms in the atmosphere, estimated to emit 700–1,400 Gg of bacteria-carrying particles into the atmosphere per year (Griffin et al, 2006; Griffin, 2007; Burrows et al, 2009a). Several previous studies have attempted to identify the parameters affecting the composition of the aerobiome and to assess the degree of their influence on the overall community composition (Mazar et al, 2016; Gat et al, 2017; Tignat-Perrier et al, 2019). Among these parameters, aerosol source and sampled air-mass trajectory were found to be of significance in determining the composition of the aerobiome observed at different sites

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