Bacteria are truly abundant across the Earth’s surface, from the soil to the oceans. The microbial population of the air that surrounds us is relatively unknown, but a research expedition led by PolyU scientists is about to vary that. After nearly a decade of effort, they’ve compiled a comprehensive map of the world’s airborne microbes, providing fresh insights into how these species interact with the surface environment – in addition to their likely future changes.

A cubic metre of “empty” air incorporates 10,000 bacteria or more, and interest within the role of air as a habitat – not merely a conduit – for microbes has grown enormously for the reason that start of the COVID-19 pandemic. In collaboration with researchers on the mainland and the US, the PolyU-led team spent around a yr sampling airborne microbes internationally, from ground level to mountaintops. Combining their very own results with essentially the most accurate global data collected in past studies, they and their research partners compiled the first-ever atlas of the worldwide airborne microbiome.

The atlas provides a wealth of insights into the microbial communities floating above the bottom. There isn’t a doubt that the air is a novel harbour of bacterial life. Genetic evaluation by the team showed that the core communities – the handful of species that form an outsized proportion of the microbe population – weren’t the identical within the air as those in marine or soil ecosystems. Actually, regardless that the air is a free-flowing medium with seemingly no internal boundaries, these core bacterial communities are distinctly localised and stable.

The research team analyzed the bacterial communities of 370 individual air particulate samples collected from 63 sites around the globe, starting from those at ground level (1.5 – 2 m high) to rooftops (5 – 25 m high) and high mountains (5,238 m asl), in addition to from densely populated urban centres to the Arctic   who led the research team, said, “We’ve got verified that human activities have actually modified the structure of microbiomes within the natural ambient air, particularly with the next abundance of pathogenic bacteria in urban air. Having experienced the pandemic for 3 years, people now pay more attention to this invisible but influential microbial community. The research outcomes could possibly be served as a critical reference for predicting planetary microbiome responses and the health impacts of inhalable microbiomes with future environmental changes.”

The researchers estimate that the overall variety of microbes occupying the ocean or soil is hundreds of times larger than those within the air. Nonetheless, the aerial diversity of microbes – often known as “richness” – is just as high. This means that surface habitats directly contribute microbes to the air. Overturning previous assumptions, vegetation is just not the foremost terrestrial source of airborne bacteria, and the Earth’s vast tracts of soil provide very small fraction. The crashing of waves, the shaking of leaves, and even frequent activities and constant respiration of animals and humans are larger drivers of bacterial exchange between the surface and the air.

Macroscopic life, notably animals and plants, is most diverse in equatorial regions (consider, for instance, warm and wet rainforests), and its diversity decreases closer to the poles. For microbes, the image is more interesting – moving from the equator, diversity maximises at mid-latitudes before falling away again. This pattern was well established for terrestrial and aquatic microorganisms, but the brand new atlas confirms that it applies to the airborne microbiome, too. The authors surmise that the “bump” in diversity at mid-latitudes is brought on by stronger sources of microbial input to those regions.

Overall, the researchers estimate that half of airborne bacteria originate from ground sources. Urban air has especially high rates of human-associated bacteria – some harmless, others pathogenic. Direct transfer of germs from people to air is just not our only effect on the airborne microbial world. Broad-scale activities similar to industrialisation disrupt natural environments and impact air quality. This weakens the environment’s “filter” effect on microbial structure, making the composition of airborne bacteria more affected by random processes – although weather still plays a crucial role too.

The close relationship between modern human activities and the microbes around us underscores the necessity to predict future changes accurately. The inhalable infectious bacteria that proliferate in cities are particularly of concern considering rapid urbanization and our growing understanding of airborne contagion, spurred by COVID-19 research. Climate change is one other impetus, given the marked effect of temperature on microbial richness, as revealed by the atlas. Hence, the study provides a useful resource and a crucial recent perspective for future public health research.

The PolyU team collaborated with Prof. James M. TIEDJE, University Distinguished Professor at Michigan State University and scientists from mainland China within the study. The findings were published within the Proceedings of the National Academy of Sciences (https://www.pnas.org/doi/full/10.1073/pnas.2204465119), a peer-reviewed journal of the USA National Academy of Sciences.

Source:

The Hong Kong Polytechnic University

Journal reference:

Zhao, J., et al. (2022) Global airborne bacterial community—interactions with Earth’s microbiomes and anthropogenic activities. Proceedings of the National Academy of Sciences. doi.org/10.1073/pnas.2204465119.