The bugs you breathe in vary by season

Researchers in Spain have demonstrated seasonal changes in the population of microbes that swirl through the air.

In rain and snow samples taken every two weeks over seven years, a team led by Emilio Casamayor at the Spanish Council for Research, in Blanes, surveyed bacteria, archaea, protists, and fungi to find patterns in what is called the airborne microbiome.

“Consistent microbial seasonal patterns were observed with highly divergent summer and winter communities recurrent in time,” the researchers write in the journal Proceedings of the National Academy of Sciences.

To track the presence of microbes, the researchers sequenced two types of ribosomal ribonucleic acid (rRNA) – substances present in all living organisms and essential for protein manufacture – called 16S and 18S.

The first is found primarily in prokaryotes, such as bacteria, while the second is found in eukaryotes, such as plants and animals.

The researchers found that, in winter, the airborne population “predominantly included bacteria closely related to terrestrial, forest, and marine biomes,” whereas the in summer it was characterised by microbial eukaryotes from freshwater. Autumn saw a greater proportion of “forest-related biomes”.

The eukaryotes were primarily made up of fungi. Casamayor and colleagues found roughly 1200 airborne bacterial genera, although they note that only 12 of them were “widespread.”

From their location in northeast Spain, the researchers tracked airflow “clusters” from the Atlantic, Europe, regional recirculation, Africa, and the Mediterranean.

They say their findings add to calls for additional research on the global airborne microbiome.

“Since high amounts of microbes are injected into the atmosphere annually, and aerosol loads are potentially increasing due in part to the deforestation and transformation of Earth’s surface into deserts, the need to establish a global sampling network to monitor airborne microbes has been recently encouraged,” they write.

“The increase in global microbial mass movements may exacerbate changes in ecosystem services and biogeochemical cycling in several unpredictable ways.”

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