In a landmark study of airborne microorganisms from the ground up to 3,500 meters, scientists from the Singapore Center for Environmental Life Science Engineering (SCELSE) at the Technological University of Nanyang, Singapore (NTU Singapore) have discovered that bacteria and fungi populate the planet’s lower atmosphere in very specific ways and, if altered, can negatively impact human health and food supply.
Using a combination of a 200-meter weather tower and a research aircraft that rotated at different heights from 300 meters to 3,500 meters to gather the necessary measurements, the researchers found that temperature was the most important factor. influencing the composition of airborne microbial communities.
As the air temperature changes, the species found and the bacteria/fungi ratio changes significantly. These results suggest that the currently observed global temperature increase will impact the atmospheric microbial ecosystem, as well as terrestrial and aquatic planetary ecosystems.
The study was published today in the peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS) by a team of interdisciplinary scientists led by Professor NTU Stephan Schuster, Research Director (Meta-‘omics & Microbiomes) at SCELSE.
Atmospheric microorganisms, collectively known as the air microbiome, are made up of bacteria and fungi and remain largely airborne once they are expelled from the planet’s surface.
Only a fraction of these micro-organisms come back to the surface, when they are carried away by rain droplets or fall with larger particles such as grains of sand or dust.
“Our research has generated a comprehensive ‘vertical map’ of microorganisms suspended in the planet’s atmosphere,” said Professor Schuster, corresponding author of the study.
“We have discovered that the composition of the air microbiome in our atmosphere is determined by temperature. As global air temperatures increase due to climate change, this could lead to very significant changes in the microbiome of the air. air with serious consequences for people and the planet.”
“If the composition of the air microbiome changes on a global scale, it may affect human health, exacerbate respiratory syndromes in susceptible patients, or it could affect the yield of agricultural crops, which then threatens our food security. Natural processes that have been working for thousands of years like this planet’s carbon cycle can also be altered.”
“With our latest research paper, we are getting closer to demonstrating that the air has its own microbial ecosystem, just like those on land and in the sea. We expect that changes in the air microbiome will have also ripple effects on land and water ecosystems,” adds Professor Schuster.
The vertical map of microorganisms also provides a starting point for future ecological investigations and necessary actions not only for the protection of global environments, but also for agricultural production sites, which may be negatively impacted by changes in communities. airborne microbes.
With the new dataset as a baseline, scientists can also model and predict changes in the air microbiome if temperatures were to rise by two degrees or more, the research team said.
To measure the microbiome in the air above ground, the team used a specialized research aircraft from the Technische Universität Braunschweig, Germany, to collect synchronized measurements of meteorological parameters and samples of airborne biomass in the air. air up to a height of 3,500 meters.
The research team on board the aircraft coordinated sampling times with a team stationed at the 200-meter-tall weather tower at the Karlsruhe Institute of Technology (KIT) in Karlsruhe, Germany.
A total of 480 vertical air samples were taken in Germany, which were brought back to Singapore for analysis. The team was surprised to find that the composition of microorganisms above 1,000 meters was stable, regardless of day or night. These layers of air act as a “well in the sky”, where bacteria accumulate in greater numbers than on the ground. The team identified more than 10,000 different species of airborne microbes from the samples taken above 1,000 meters.
This was very different from air samples taken below 300 meters, which were found to follow the 24-hour day and night cycle (called the daily cycle), where the composition of the air changes due to bacteria and certain fungi dominating during the day, to lignivorous fungi dominating at night.
The discovery of the daily cycle of airborne microorganisms was first published in PNAS in 2019when the same research team studied tropical air in Singapore using air samples taken from different levels of a 50-story residential building named Pinnacle@Duxton.
In their latest study, the team also reported that atmospheric turbulence – wind and weather – is the primary driver of microbial aerosol dynamics, which determines how microorganisms in the air are distributed.
Driven by day/night temperature changes, air masses stratify (stratify) at night and mix during the day, resulting in stratification of the air microbiome at different heights of the lower part of the air. atmosphere.
“For the first time, meteorological and biological data from the atmosphere were measured in unison, allowing us to develop a comprehensive hypothesis on the effects of atmospheric turbulence on the dispersal of microorganisms in the lower atmosphere,” Professor Schuster said.
The researchers further noticed that the upper layers of air contained up to 20 times higher concentration of radio-tolerant bacteria, known to be resistant to ionizing radiation, desiccation, UV rays or oxidizing agents. Among these bacteria, a species known as Deinococcus radiodurans is known to withstand a radiation dose 1,000 times that of the human body.
The team hypothesized that ionizing radiation from the sun and space contributed to the development of radioactive tolerance in these bacteria at greater heights, whereas the bacteria on the ground were not exposed to high levels. such levels of radiation.
Sampling for airborne life on Mars?
Based on their experiments, the researchers comment that their air-sampling technologies could in principle be used to study the atmosphere of nearby planets, such as Mars.
By exploiting the knowledge that microorganisms will aggregate in a planet’s atmosphere, it could provide an alternative to the current method of sampling, which is done by a robotic vehicle drilling and collecting soil samples.
For example, a robot equipped with an air sampler could collect microorganisms from the atmosphere by trapping them in an air filter and returning the filter to Earth, on a possible future return mission from Earth. samples on Mars.
The study of the air microbiome is one of the flagship research projects of the SCLSE along with its research on terrestrial and aquatic ecosystems. The project was carried out over eight years and resulted in more than 40 articles, leading to these results. The air microbiome research was supported by a Tier 3 grant from the Singapore Ministry of Education, SCELSE and NTU.
Sustainability, climate change and the environment are key research pillars for NTU Singapore and part of its Sustainability Manifesto launched last year. The University will pursue basic and applied research to develop sustainable solutions that can mitigate the effects of natural disasters and climate change, and to meet the demand for food with alternative food sources.
Over the past two years during the pandemic, Professor Schuster and his team have pivoted to using their air sampling technology to detect and analyze the SARS-COV-2 virus from indoor air, a technique that has demonstrated greater sensitivity than surface swab tests.
In the future, the team plans to conduct more vertical studies of the air column in the tropics as well as at higher altitudes to improve and expand their “atmospheric microbiome map”.
 “The microbial communities of the tropical air ecosystem follow a precise daily cycle”, PNAS, October 29, 2019.