This text is based on a press release by the Max Planck Institute for Chemistry.
Saharan dust carries bacteria across the Atlantic and alters the microbiome over the rainforest
- Air masses carry microorganisms from African arid regions across the Atlantic into the Amazon rainforest. There, the bacterial composition of the air changes, while the fungal spore community remains stable.
- Saharan dust also carries potentially harmful endotoxins into the region, causing their concentration to triple.
- Further studies are needed to determine whether the transported microbes remain viable after their long journey and what consequences their presence may have for health and the environment.
When viewed under a microscope, there is a lot of activity above the Amazon rainforest. The air is full of pollen, fungal spores, tiny plant particles, and bacteria. Normally, the composition of this bioaerosol community is quite stable. A team that included researchers from the University of Graz, the Max Planck Institute for Chemistry in Mainz and Brazilian partner institutions has now shown that microorganisms are transported across the Atlantic along with desert dust from the Sahara. According to the study, which is being published in the scientific journal ´Nature Communications Earth & Environment´, the bacterial composition of the air changes significantly when dust clouds from Africa reach the rainforest. The composition of fungal spores in the Amazon’s air, however, remains largely the same.
Transport of Bacteria Across the Atlantic Confirmed
In February 2020, a team led by Bettina Weber of the University of Graz collected aerosol samples daily over a three-week period at various altitudes above the Amazon rainforest in Brazil. During five of these days, the researchers registered the transport of desert dust from North Africa into the region. The researchers conducted genetic analyses of the collected samples to determine their microbiological composition, particularly with regard to the bacteria and fungi they contained.
Following the dust influx, the researchers found numerous bacteria on the filter samples that typically occur in dry soils, in addition to “native” bacteria. The researchers attribute the fact that the fungal community remained largely unchanged to the large quantities of spores released by the rainforest, meaning that fungal spores from the Sahara did not significantly affect the analyses.
“Soils in arid regions and deserts are largely colonized by microbial communities, known as biological soil crusts. Genetically, the bacteria match organisms from the Sahara, which proves that they are transported from African biocrusts across the Atlantic by wind all the way to Brazil’s rainforest,” explains study leader Bettina Weber, who is a professor at the University of Graz and collaborates closely with the Max Planck Institute for Chemistry.
© Cybelli Barbosa, MPIC
Potential pathogens are traveling with
In addition, the scientists found that the concentration of endotoxins in the air tripled with the arrival of Saharan dust. Endotoxins are found in the cell membranes of certain bacteria and are released when the bacteria die. In humans, these chemically stable compounds can lead to inflammation.
“I was surprised by the large amount of endotoxins in the air,” comments Jens Weber, who conducted the research as part of his doctoral studies. “Previous studies in the Caribbean have shown that asthma attacks often increase when Saharan dust arrives. Whether a similar correlation exists in the Amazon remains to be investigated.”
Further studies in the coming years will aim to clarify which microorganisms are present in the dust and whether they play a relevant role in human health. Furthermore, the researchers plan to investigate whether the microbes are still viable after their days-long journey across the Atlantic.
Weber et al. published the study “Amazonian rainforest bioaerosol influenced by African dust intrusion” in the journal Nature Communications Earth & Environment
© Jens Weber, MPIC
Background
About Aerosols
Aerosols are solid or liquid particles in the atmosphere that are important for climate and weather, as they can act as cloud condensation nuclei or ice nuclei. Bioaerosols are of biological origin and comprise a very diverse range of cells (e.g., from bacteria), spores (e.g., from fungi, mosses, ferns), and animal and plant debris. In addition to the importance of bioaerosols for atmospheric processes, the transport of biological material such as bacterial cells and fungal spores can contribute to their global spread. However, the current study does not yet resolve whether the collected genetic material is still viable.
Method
For the study, the team installed dust filter samplers at two different heights (42 and 323 meters) on the ATTO research tower. The filters collected dust and genetic material from microorganisms. Using filter samples collected before and after the dust event, the researchers determined which bacteria and fungi are typically present in the air—the microbiological background profile.
To determine the endotoxin concentration in the air, the researchers used a highly sensitive enzymatic method known as the “kinetic chromogenic Limulus amebocyte lysate (LAL) method”.
The origin of the dust was determined using an atmospheric science computational method that identifies the geographic origin and transport path of air masses. The analysis revealed that the transport of the air masses from Africa to South America took about ten days.
To clarify the origin of the dust, the researchers determined the mineral “footprint” of the samples. The calcium ion content, for example, indicates a high calcite content, which is typical for mineral dust from the Sahara.
Collaboration
The study was conducted in collaboration with various institutions in Brazil. Researchers in Lausanne, Switzerland, determined the ion concentrations.
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