It has been estimated that 80–120 tn of dust per year are carried across the Mediterranean towards Europe, with dust clouds recorded to reaching an altitude of up to 8 km the Mediterranean basin 24, 25, 26.ĭespite the importance of the aerial microbial dispersion phenomena, studies dealing with the microbial ecology associated to African dust are very limited, being almost nonexistent in southern European areas. This intrusions account for ~50% of global dust production 23. However, the southern Mediterranean is the most influenced areas by atmospheric intrusions of Saharan dust 18, 22.
Large dust storm events that originate from North Africa are capable of continent-wide, transoceanic, and global dispersion 13, 17 and frequently affect air quality in Africa, the Middle East, Europe, Asia, the Caribbean, and the Americas 15, 16, 18, 19, 20, 21.
The Sahara-Sahel regions of North Africa are the dominant sources of aerosolized soil dust in the North Hemisphere atmosphere (50 to 75% of the current estimate), contributing as much as one billion metric tons of dust per year to the atmosphere 13, 18. Thus, desert dust clouds may serve not only as a source of nutrients for terrestrial plants and primary producers in nutrient depleted oceanic waters 15, 16, but may also serve as a vehicle for global transport of microorganisms, including pathogens 13, 17. Several studies have also demonstrated the potential for microorganisms to be transported over long distances through the atmosphere, associated to desert dust, as a route for the colonization of new habitats 13, 14. Additionally, the atmosphere is one of the most extreme environments and microorganisms inhabiting in the troposphere are exposed to higher UV radiation, desiccation, cold temperatures and nutrient deprivation than in other environments 11, 12. However, more recent studies, incorporating direct counting by microscopy or quantitative PCR 9, have yielded, more accurate, higher estimates of the abundance of airborne microbes and seasonal patterns 10. Global abundance of aerial microorganisms has been estimated, based on data from terrestrial environments, to range between 10 4 to 10 6 m −3 8. Likewise, airborne bacteria can have important effects on human health, producing allergic asthma and seasonal allergies, and could interfere in the productivity of managed and natural ecosystems 7. clouds and snow formation or precipitation patterns alterations) 2, 3, as well as in the long-range dispersal of plant and livestock pathogens 4, 5 and in the maintenance of the diversity in aquatic systems 6. In this case, Brevundimonas, and Methylobacterium as well as Cupriavidus and Mesorizobium were the most abundant genera.Īirborne microbes are ubiquitous in the atmosphere 1 and are thought to play important roles in meteorological processes (i.e. Samples taken during the flights carried out 15 days after the dust event were much more similar to the dust event samples compared with the remaining samples. After the dust intrusion, Rhizobium was the most abundant genus, (40–90% total sequences). Most of these taxa are well known for being extremely stress-resistant. The most abundant bacterial species during the dust event, grouped in three different phyla: (a) Proteobacteria: Rhizobiales, Sphingomonadales, Rhodobacterales, (b) Actinobacteria: Geodermatophilaceae (c) Firmicutes: Bacillaceae. Samples related in height or time scale seems to show more similar community composition patterns compared with unrelated samples. Samples were collected during dust and dust-free air masses as well two weeks after the dust event. Samples from different open-air altitudes (surface, 100 m and 3 km), were obtained onboard the National Institute for Aerospace Technology (INTA) C-212 aircrafts. We have analyzed the bacterial community of a large Saharan dust event in the Iberian Peninsula and, for the first time, we offer new insights regarding the bacterial distribution at different altitudes of the lower troposphere and the replacement of the microbial airborne structure as the dust event receeds.
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