Microbial Smog

Some 1,300 species of microbes, including some associated with allergies and lung disease, are adrift in Beijing’s thick smog.

By Jef Akst | February 3, 2014

Smog over Beijing's Forbidden CityWIKIMEDIA, BRIAN JEFFERY BEGGERLYThe brown haze that covers Beijing and surrounding areas is home to some 1,300 microbial species, according to a group of researchers in China who used genome sequencing to identify the biological makeup of a particularly thick January 2013 smog. While most of these species are believed to be harmless, some have been linked to allergies and respiratory disease in humans, the researchers reported last month (January 23) in Environmental Science & Technology.

“It’s a proof of principle that one can extract and identify these microbes at the species level,” coauthor Ting Zhu, a biologist at Tsinghua University in Beijing, told Nature. “It adds to our understanding of what we inhale every day.”

Over the course of a week during a severe smog event, Zhu and colleagues took 14 air samples, then filtered them based on size to isolate microorganisms less than 2.5 micrometers (PM2.5) and those up to 10 micrometers (PM10). On some days, the researchers measured PM2.5 levels at greater than 500 micrograms per cubic meter—20 times the World Health Organization’s air quality guidelines.

Extracting and sequencing DNA from the samples, the researchers were able to identify some 1,300 different microbial species, including the pneumonia-causing Streptococcus pneumonia, the fungal allergen Aspergillus fumigatus, and a variety of bacteria commonly found in feces. On the smoggiest of days, the proportion of DNA from these allergens and pathogens increased by two to four times relative to DNA from harmless microbes. Zhu told Nature that some of the DNA likely came from dead cells, “so we don’t know if they are still viable,” but even so, the findings point to the potential health risk of severe smog events, particularly for the elderly or immunocompromised.

“There is increasing evidence that bacteria could play an important role in the health effects,” Andrea Franzetti, a microbiologist at the University of Milan-Bicocca, Italy, who has surveyed airborne bacteria in his home city, told Nature.

Correction (February 5, 2014): This story has been updated from its original version to correctly reflect that microbes are divided into those that are less that 2.5 micrometers and those up to 10 micrometers, not millimeters. The Scientist regrets the error.

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Avatar of: artmez


Posts: 10

February 4, 2014

Two points:

[1] mm is millimeters and not micrometers. I doubt that the particulants in the air were 2.5mm or 0.1inch in size, even if a nearby volcano were spewing ash at the moment let alone 10mm in size.

[2] The statement: "bacteria commonly found in feces" is grossly misleading in its inference. Water is found in feces and that does not mean that all water is from feces.

But interesting none the less. How about similar tests in cities like New York, London, Paris, Moscow? How do they compare?

Avatar of: Dr Edo

Dr Edo

Posts: 30

February 5, 2014

A major public health problem being faced by the Chinese people is that of antibiotic resistance. It would be of interest to see if any of the more likely pathogens found in these atmospheric studies, including those mentioned in the article are multi-drug resistant. Keep in mind that recent reports coming out of China acknowledge that their sewer plants are generating resistant organisms and then releasing them to the environment----usually the aquatic environment. Less well understood is the fact that sewer plants, as typically designed, are major aerosol generators. Thus, these plants lift into the surrounding atmosphere very large volumes of microbes and these because of their size can be easily lofted and thendrift for miles into surrounding areas.


Dr Edo McGowan

Avatar of: Jef


Posts: 809

Replied to a comment from artmez made on February 4, 2014

February 5, 2014

Hi Artmez. Thank you for pointing out the mistake in the units used to classify microbes. The story has been fixed and a correction appended.

Thanks for reading!

Jef Akst, editor, The Scientist

Avatar of: Jinguo W

Jinguo W

Posts: 1

February 5, 2014

I am curious to know the origin of these smog.Are bugs included during smog formation or those particles adsorbed bacteria while floating in the air? Jinguo

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