Life in the sky: What shapes microbial communities in the air?

Microbes are constantly present in the air, but little is known about how these diverse communities are influenced by their environment—a topic of growing interest in the face of climate change. Scientists discovered that seasonality appeared to enhance biodiversity during the warmer months, and local urbanized landscapes contributed to less airborne diversity when compared to more vegetative locations. This data reflects a chapter in the evolution of biodiversity in airborne microbial communities, and may help us to predict the changes that could be associated with anthropogenic climate change.

There is one group of organisms that dominates all life on Earth. They are found across all terrains, in our atmosphere, underwater, and even deep within the Earth’s crust. Amassing over 93 gigatons of Earth’s biomass carbon, scientists estimate that there are close to a trillion microbial species on our planet, many of which are still unknown.

However, the vast diversity of microbial communities is not stagnant, but rather they experience fluctuations throughout space and time. As a result, we unearth another question of how this diversity came to be, and the environmental factors that shape the composition of these communities.

If we focus on microbial populations in our atmosphere, several possibilities arise for environmental drivers of diversity as seen in the figure below. The types of species found in the atmosphere fluctuates constantly—while some are ever-present, others only remain in the air for certain life stages like reproduction. When considering all the possibilities that may shape diversity, variables like latitude, seasonality, climate, and geographic location may all play a role. For instance, what role does landscape composition have on airborne bacterial diversity? Could human-mediated modification of landscapes through urbanization be detrimental to this diversity? Answering these sorts of questions may provide insight into how life on Earth will adapt to the ongoing crisis of anthropogenic climate change.

Figure made with BioRender.

Airborne microbial communities exhibit great diversity, although the environmental factors that influence their composition are still unclear. Variations in seasonality and geographical location may have some contribution to the changing diversity exhibited in these communities.

A study carried out by Karlsson et al. (2020) examined the factors that shaped the diversity of airborne microbial communities in Northern, and Southern Sweden (Kiruna and Ljungbyhed respectively) over a two year timeline. They focused on how seasonality and geographic location influenced both bacterial, and fungal composition in the air. They innovatively utilized air filters through the Swedish radioactive fallout monitoring program (used to measure radioactive contaminants from nuclear testing) to collect air samples across temporal, and geographic scales. They isolated the environmental DNA (eDNA) obtained from these samples—the DNA that is released from organisms in a particular environment—to carry out a metabarcoding analysis. Specific regions of the DNA samples were sequenced in order to identify each unique microbial species, and track how the diversity in airborne populations was changing.

They discovered that overall, geographic location played a larger role than seasonality in shaping bacterial communities, and seasonality largely influenced fungal populations as shown in the figure below (panel E). As well, both communities showcased relatively higher diversity in the warmer months of spring, summer, and fall, with the lowest diversity observed in the winter. Overall, it is apparent that there are fascinating correlations between environmental factors like seasonality and location, with the ever-changing dynamics of airborne microbial populations.

E.

Modified from Karlsson et al. (2020).

A-B: Species richness in airborne bacterial communities based on observed OTUs (operational taxonomic units, the equivalent of species for bacteria) respective to Kiruna (A) and Ljungbyhed (B) in Sweden (black line) over the course of two years. Weeks corresponding to seasonality are indicated by coloured dots (winter: blue, spring: yellow, summer: green, autumn: red), and average weekly temperatures are indicated by the brown line. Peak diversity across both locations was seen in the summer and autumn months, and the lowest diversity was seen in the winter. C-D: Species richness in airborne fungal communities based on observed OTUs respective to Kiruna (C) and Ljungbyhed (D). Peak diversity across both locations was seen in the summer and autumn months, and the lowest diversity was seen in the winter. E: Overall percent variation in biodiversity of bacterial and fungal communities attributable to geographic location (Kiruna, Ljungbyhed), and seasonality. The location explains more biodiversity for bacteria than for fungi.

 Commenting on the most difficult challenge encountered in this study, Dr. Per Stenberg, the lead researcher, stated “By far the most challenging problem was how to extract DNA from all types of organisms in all stages of decomposition. If we treated the samples too hard, DNA from cell fragments, or “naked” DNA gets destroyed. If we treated the samples too mild, we would not be able to access [the] DNA inside (e.g. tough spores and pollen).”

Dr. Stenberg elaborated, “We spent about two years optimizing this, and ended up with a procedure where we took three pieces of each sample, and treated them in three separate ways before pooling them in the end.”

Beyond the general relationship of temporal and geographic variation with diversity, the paper presented some other compelling findings. Interestingly, the terrain composition of a specific location appears to show some correlation to the microbial diversity in the air. The Southern locality of Ljungbyhed is more urbanized, whilst the Northern town of Kiruna is far more diverse in vegetation, and hence significantly more microbial diversity is observed. Additionally, weather patterns such as humidity appeared to be inversely proportional to bacterial diversity in Ljungbyhed. The authors suggested that the lack of diverse vegetation, and large agricultural presence in the town may have provided the arid conditions necessary for airborne bacteria to disperse efficiently. Hence, we see how modification of landscapes through human activity can drastically shape the types of microbes in our air.

Thus, another question arises about the relationship between urbanization and microbial diversity—an important inquiry in the face of anthropogenic climate change, and peak human industrialization. Dr. Stenberg and his research team are currently working on reproducing the study at a larger scale to encompass a 50 year timeline of samples across six diverse areas of Sweden. As more of these questions are answered, and more data is uncovered, we may finally begin to predict just how consequential our climate crisis really is for life on Earth.

Learn more about microbial diversity
  1. Swedish Biodiversity In Time and Space
  2. There are more microbial species on Earth than stars in the galaxy
  3. Humans make up just 1/10,000 of Earth’s biomass
  4. Earth may be home to a trillion species of microbes
References
  1. Karlsson, E., Johansson, A.-M., Ahlinder, J., Lundkvist, M. J., Singh, N. J., Brodin, T., Forsman, M., & Stenberg, P. (2020). Airborne microbial biodiversity and seasonality in Northern and Southern Sweden. PeerJ, 8, e8424. https://doi.org/10.7717/peerj.8424
  2. http://large.stanford.edu/courses/2014/ph241/eller1/docs/air.pdf

About the Author

This post was written by Siham Karamali. She is completing her final undergraduate year studying Molecular Biology and Biotechnology with a Minor in Environmental Management, aspiring to continue in the biomedical technology field. Although limited because of the pandemic, she enjoys going on hikes to do some nature photography. You can also find her painting and playing the piano in her free time.

One thought on “Life in the sky: What shapes microbial communities in the air?

  1. Amazing post! Learned a lot, and I think studies such as this will be really relevant both now and in the future, especially with the increasing importance on research regarding both microbial communities, and the environment! Also, great job on getting a quote from the researcher, integrating it, and giving readers something to think about with your final sentence! Good luck with your future endeavours!

    Liked by 1 person

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