Chinese team now develops a better understanding of microbes in the air

When people talk about air pollution, PM2.5 nowadays immediately comes into mind. Yet, we are often not aware that these tiny particles "flying" in the air could be living microbes, e.g., bacteria, fungal spores, and viruses. Some of these alive particles could be human pathogens or opportunistic ones which can cause serious health outcomes. In addition to health effects, these airborne microbes also have direct impact on cloud formation and climate arising from their special attributes. Virtually, any microbes originated from earth surfaces, e.g., sea, land, forest, agriculture, animals, and humans, could be released into the air due to the disturbance and then remain airborne for a sustained amount of time. Accordingly, we are constantly breathing in microbes from the air. These microbes can be also transported far away from their original sources because of atmospheric air movements. Over the past decades, the chemical compositions of particulate matter have been extensively studied, especially in mega cities; however, despite of their importance few studies were conducted for their biological counterparts, especially on a larger scale. Information about their size distribution and concentration is significantly lacking especially in different climate zones.

A Chinese team led by Prof. Maosheng Yao from College of Environmental Sciences and Engineering, Peking University now develops a better understanding of microbes by deploying a fluorescence-based microbial aerosol sensor, called Ultraviolet-Aerodynamic Particle Sizer (UV-APS), which was transported using an automobile, to many parts of China, including regions from 13 provinces. The UV-APS detects the size distribution and concentration level of viable microbial aerosol particles by measuring their intrinsic fluorescence level emitted. In previous studies, most of the monitoring was confined to single location which is often in a pristine environment, thus only representing those of natural emissions. They monitored the microbial aerosol levels in major cities (highly polluted) and their suburbs (less polluted) (total 40 locations) in 11 provinces (7 different climate zones) of China. In addition, they also studied the bacterial aerosol structures using a gene sequence technique.

The team reported their findings in Science Bulletin (Wei et al., Sci. Bull. (2015) 60(16):1439-1447). "In average, we have detected about 104-105 viable microbial aerosol particles per m3 in the ambient air, and Bacillus was found to dominate the bacterial community. For different geophysical locations, the microbes in the air have strikingly different size distribution patterns, e.g., some of them have a peak size at 3 µm, e.g., Gansu province, the north-western part of China, while others have fluorescent peaks at sizes close to 1, 1.5 or 4 µm. These differences are largely attributed to the different climatic conditions, e.g., temperature, humidity level and rainfall. These unique microbial aerosol distribution patterns might serve as a fingerprint for a particular region." says Prof. Yao.

In the past, scientists studied viable microbial aerosols in pristine environments, e.g., in Amazon basin, using the same method, and detected an average viable bioaerosol concentration of 7.3 x 104/m3, which accounts for 24% of the total particle number and 47% of total mass. Yet, no studies were conducted for microbial aerosol characteristics in mega cities with a high level of air pollution, e.g., Beijing. Now, the team discovered that locations with a higher level of air pollutions also tend to exhibit a higher level of airborne bacterial diversity and concentration. "We also found that indoor environments have at least 10 times higher, sometimes up to 100 times, fluorescent particle concentration levels compared to the ambient air," Prof. Yao adds. "However, due to the instrumentation limitation, the real microbial aerosol concentration could be overestimated as a result of the interferences from chemicals such as polycyclic aromatic hydrocarbon (PAH)." Jing Li, a PhD student from the team, also adds "We have detected significant differences in bacterial aerosol community structures for different climate zones in China using an automobile air conditioning filter method. For example, Hainan has a very fewer bacterial aerosol diversity compared to that in Beijing."

"We are also puzzled that we saw a significant increase in the level of fluorescent bioaerosol particles at the right occurrence of a haze event in Beijing, but subsequently a decline in their concentration was observed over the progress of the haze. We are now investigating the relevant mechanisms in another work, "says Kai Wei, the lead author of the paper, a PhD student from College of Environmental Sciences and Engineering, Peking University. Fangxia Shen, also a member of the team, but now a postdoctoral researcher at Max-Planck Institute for Chemistry in Mainz, Germany, says "the viability of airborne microbes could be severely affected during an episode of heavy air pollution, especially those occurring in China. The microbial aerosol characteristics could be very different in Mainz from those in Beijing."

Yunhao Zheng, another graduate student from the team and also a co-author of the paper, adds "One of my projects is to find out if there is a link between air pollution and increased number of hospital visits, especially those related to respiratory infections, using a DNA-based multiplex pathogen detection method. We hope to provide clues why people often get infected"

"Information of the viable bioaerosol levels in the ambient air in China could be potentially useful to speciation of the PM sources especially for Chinese air pollution, and also helpful in understanding its impacts on local climate and ecology. The data obtained from the study can be also used to construct atmospheric models for bioaerosol emissions at various scales," says Chang-Yu Wu, a Professor from University of Florida, USA, and also a co-author of the paper. "Certainly, it is exciting to have this type of information in the academic community."

"Although the results from this work are limited to short-term monitoring at each particular location this is the first ever attempt in understanding the airborne microbial community on such a large scale. Certainly, more in-depth studies are needed to elucidate the impacts of these microbes from the air on our health, ecology and climate." Prof. Yao adds.

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Reference

Kai Wei,Yunhao Zheng, Jing Li,Fangxia Shen, Zhuanglei Zou,Hanqing Fan, Xinyue Li,Chang-yu Wu, and Maosheng Yao (2015), Microbial Aerosol Characteristics in Highly Polluted and Near Pristine Environments Featuring Different Climatic Conditions, Science Bulletin, (2015) 60(16):1439-1447.

http://www.scibull.com:8080/EN/abstract/abstract509941.shtml

http://link.springer.com/article/10.1007%2Fs11434-015-0868-y

Science China Press
http://www.scichina.com/

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