A study by CEAB-CSIC and CREAF, based on samples collected over thirty years, has revealed that bacteria and fungi from North African deserts have a persistent presence in southern Europe, regardless of Saharan dust episodes. This finding confirms that their impact on ecosystems and human health is not occasional but continuous.
The research was conducted using rain samples collected from 1987 to 2014 in the Montseny Massif. Desert dust (which contains microorganisms that remain alive) constantly travels thousands of kilometres within persistent currents in the upper layers of the atmosphere. Eventually, it falls with rain or snow, which carries it to the ground. By analysing precipitation samples and satellite data, scientists can identify which microbes have travelled intercontinental distances. To avoid confusion with local pollution, which is concentrated in lower layers, samples are collected in mountainous areas, where rain only carries particles from the upper atmosphere, ensuring that the analysis reflects exclusively microorganisms transported by long-range atmospheric currents.
To characterize the microbiota, researchers analysed the DNA of rain samples using massive sequencing techniques and compared the results with soils from North African deserts and genetic data from other soils worldwide. For the research, they also used computer simulations to recreate the movement of large air masses that disperse microorganisms on a global scale.
The results, covering 30 years of data, have been compiled and published in a scientific article this February in Environmental Microbiology. The study demonstrates that bacteria and fungi from North African desert soils are always present in samples throughout the entire period, and therefore continuously in our air, even long after large Saharan dust injections. It highlights the importance of ongoing processes in the upper layers of the atmosphere and contradicts the perception, derived from previous aerobiological studies, that the microbiota present in local environments is mainly generated by neighbouring ecosystems. Recognizing the sustained presence of distant microorganisms in our air is key to evaluating their effects on both natural environments and human health.
The lead author of the study, Joan Cáliz, a researcher at the Centre for Advanced Studies of Blanes (CEAB-CSIC), explains that “this phenomenon is related to the ability of particles generated in the Saharan region near the low-pressure belt of the intertropical front to ascend to great heights and remain suspended, like plankton, with a very low sedimentation rate. This mechanism likely occurs in other arid regions of the planet as well, generating similar situations.”
Co-author Anna Àvila, a researcher at the Centre for Ecological Research and Forestry Applications (CREAF), who was responsible for collecting samples throughout the entire study period, highlights that “this knowledge could not have been obtained before due to the difficulty of securing funding for long-term programs like the Montseny rain sampling project, which lasted thirty years. The knowledge we gain from long-term collections like this one underscores the importance of long-term sampling.”
The study’s director, Emili Casamayor, head of the Ecology and Complexity of the Global Microbiome Laboratory at CEAB-CSIC, points out that “these microorganisms, which persistently reach us from distant locations, can have local-scale effects—both positive (helping establish biological communities in remote environments) and negative. In previous studies, we have also confirmed that pathogens (mostly affecting plants) and antibiotic resistance genes (which have a more direct impact on human health) are present in this diffuse and persistent airborne microbiota that travels worldwide. Understanding the natural mechanisms that drive the planetary mobilization of these microorganisms, and how human activity at the local level can accelerate or mitigate it through changes in water and land use, can help reverse processes and generate scientific knowledge for the healthy management of territories.”
Researchers emphasize the importance of continuing to study these phenomena occurring in the upper layers of the atmosphere and the factors influencing them, as they have a direct impact on both nature—such as soil fertilization—and human health—such as increased allergies or the spread of antibiotic-resistant genes. This issue becomes even more relevant in the context of climate change, where arid regions are expected to expand and atmospheric circulation patterns may be altered due to human activity.
A multidisciplinary study
This research is part of the AEROSMIC project, funded by the Spanish State Research Agency (AEI) and the long-term ecological monitoring network (LTER), and has a strong cross-disciplinary component. It connects the study of microscopic life forms with the global dynamics of planet Earth. It integrates disciplines such as microbiology, physics, and meteorology to deepen our understanding of the long-range dispersal mechanisms of microorganisms, utilizing methodologies like metagenomics and biocomputation to gain a comprehensive insight into the microorganisms dispersed globally through the atmosphere.
Ref. Article: Environmental Microbiology. Persistent desert microbiota in the Southern European sky. Cáliz, Joan, Centre d’Estudis Avancats de Blanes; Menéndez-Serra, Mateu, Centre d’Estudis Avancats de Blanes/Kobenhavns Universitet Section for GeoGenetics; Triadó-Margarit, Xavier, Centre d’Estudis Avancats de Blanes; Avila, Anna; Centre de Recerca Ecologica i Aplicacions Forestals; Casamayor, Emilio; Centre d’Estudis Avancats de Blanes. https://doi.org/10.1111/1462-2920.70046. Link: https://enviromicro-journals.onlinelibrary.wiley.com/doi/full/10.1111/1462-2920.70046
L'entrada Bacteria and fungi from the Sahara: a constant presence in the southern European sky with impacts on ecosystems and Health ha aparegut primer a CEAB.