Airborne Bacterial Communities in Three East Asian Cities of China, South Korea, and Japan

Abstract

The global diversity of airborne bacteria has not yet been studied, despite its importance in human health and climate change. Here, we focused on the diversity of airborne bacteria and their correlations with meteorological/environmental conditions in China, South Korea, and Japan. Beijing (China) had more diverse airborne bacteria, followed by Seoul (South Korea) and Nagasaki (Japan), and seasonal variations were observed. Beijing and Seoul had more diverse airborne bacteria during the winter, whereas Nagasaki showed greater diversity during the summer. According to principal component analysis and Bray-Curtis similarity, higher similarity was observed between Beijing and Seoul than between Seoul and Nagasaki during all seasons except summer. Among meteorological/environmental variables, temperature and humidity were highly correlated with the diversity of airborne bacteria on the measurement day, whereas wind speeds and the frequency of northwest winds were highly correlated for 2-3-day moving averages. Thus, proximity and resuspension could enhance bacterial diversity in East Asian cities.

Figure 1

Relative abundance of airborne bacteria at the phylum level at each measurement site during the measurement period. B, S, and N indicate the Beijing, Seoul, and Nagasaki sites, respectively, and Sp., Su., Fa., and Wi. indicate the four seasons (spring, summer, fall, and winter, respectively).

Figure 2

The results of LEfSe analysis, which identified bacterial genera that were significantly abundant in one site compared with the other two sites. Bacterial genera with the LDA score of more than 3 are shown. Colours indicate the phylum level categories of these bacteria.

Figure 3

(a) Diversity versus number of reads at the species level at each measurement site. Red circles, green rectangles, and blue triangles represent the numbers of species in the Beijing, Seoul, and Nagasaki sites, respectively. (b) Diversity of the Beijing (red circles) and Seoul (green rectangles) sites divided by that of the Nagasaki site.

Figure 4

(a) Heat map of the identified phylotypes at the genus level, where identified phylotypes are in black and unidentified phylotypes are in white. Sp., Su., Fa., and Wi. indicate the four seasons (spring, summer, fall, and winter), respectively. (b) Bray-Curtis similarities of the identified phylotypes at the genus level between measurements sites and between seasons. B-S, S-N, and B-N represent comparisons between Beijing and Seoul, Seoul and Nagasaki, and Beijing and Nagasaki, respectively. Sp., Su., Fa., and Wi. indicate the four seasons, respectively.

Figure 5

Principal component analysis (PCA) at the OTU level based on the Bray-Curtis distance for all measurement samples. Samples are grouped (a) by city and (b) by season.

Figure 6

Scatter plots showing the correlation between airborne bacterial diversity and meteorological factors, such as humidity, wind speed, and temperature.