Characterization of airborne microbes associated with yellow-dust particles transported from Asian continent to Japan

Abstract:

This study demonstrates the transport of microorganisms from Chinese deserts to Japan. The high throughput approach provides the following key findings: (a) the diversity of airborne bacteria increased with dust dispersals from Chinese deserts to Japan; (b) bacterial taxa include markers associated with desert microbial communities; human and plant pathogens are also detected; (c) transit over oceanic waters and anthropogenic polluted areas strongly selects for airborne bacterial populations through atmospheric stressors. These findings have broad relevance to understanding the drivers of global microbial biogeography.


[Background]
Asian dust, also called yellow dust, is observed in Japan occasionally during spring months. Asian dust is a phenomenon in which yellow dust particles from the Gobi and Taklimakan deserts, about 4000 km apart from Japan, are kicked up by desert storms and conveyed to countries including Japan by strong Aeolian, eastward winds. With an Asian dust event, yellowish haze may prevail. In addition, Asian dust, as well as polluted particles from industrial zones along the continental coasts, can be conveyed by wind. It has also been found that Asian dust is not only conveyed together with desert bacteria but also mingled with terrestrial and marine aerosols with which microorganisms are associated. Nonetheless, many unknowns remained such as the variation among microorganisms conveyed with Asian dust and aerosols, as well as their possible human and plant pathogenicity.

[Results]
An international team of 13 scientists from 8 institutions of Japan, New Zealand, Korea and Singapore, including scientists from Kanazawa University as leading members, has investigated microorganisms, primarily bacteria, that are conveyed in association with Asian dust by eastward winds from Central Asia to Korea and Japan for about 4000 km following desert wind events.
In 2015, during 4 months from early spring to early summer where Asian dust events take place, microorganisms conveyed in association with particles were investigated at Yongin in the suburbs of Seoul, Korea, and at Yonago, Japan (Figures 1 and 2). Those particles consisted of yellow fluorescent particles (thought to represent fungal and bacterial cellular remnants and organic matters), mineral particles, microbial particles and black carbon that is probably anthropogenic. In early spring, more mineral particles of 0.2 to 30 μm were found.
It was confirmed that desert microorganisms arriving at Yongin and Yonago caused by desert wind events in Central Asia. Microorganisms from transit areas were also detected. The concentrations of microbial particles fluctuated from 3.8 × 104 to 2.0 × 106 cells/m3 in aerosols, showing covariation with desert dust levels. On haze days with Asian dust, 5 to 10 fold more microorganisms were detected than on non-haze days. The bacterial 16S rRNA gene sequences from the samples at Yongin and Yonago resolved into 282 and 245 operational taxonomic units, respectively, which were respectively composed of 21 and 27 phyla as well as 194 and 170 families. The following three key points were recognized; (1) During dust events, the airborne bacteria deposited at both Yongin and Yonago had higher richness compared to non-dust days. At the same time, the community structures were not substantially different between dust event and nondust event days. (2) The air samples collected during early spring indicated higher richness of bacterial communities than those during late spring and early summer. The airborne microbial communities showed high phylogenetic similarity (tight clustering) from early spring to late summer. (3) Yonago samples had significantly more variable bacterial recruitment from aerosols than Yongin samples. From these findings, airborne bacteria conveyed over long distance in association with dust particles showed more phylogenetic variety, and airborne bacteria in association with dust particles found at Yonago included those of marine origin, suggesting a contribution of marine aerosols. Upon long distance transport from deserts over agricultural, industrial and highly populated zones, anthropogenic particles and black carbon should be mingled with Asian dust; the present study detected contributions of bacteria from those zones in the airborne microbial community either at Yongin or at Yonago but to a moderate extent. The trajectories are, therefore, thought to be primarily through northern or southern part of China. It should be noted that human and plant pathogens were found in some samples. 

[Future prospects]
Here it is shown that dust particles from the Central Asian deserts are mingled with anthropogenic particles, both of which contribute to transport and dispersal of microorganisms. Upon transit over terrestrial and marine surfaces, the air-mass with Asian dust takes up different populations of microorganisms. These findings have broad relevance to understanding the drivers of global microbial biogeography. Since human pathogens are also detected in samples collected, it is also necessary to carefully investigate this and to monitor the possibility of outbreaks of diseases.

 

 

Figure 1.

Map of places relevant to this study and trajectories of aerosols. (a) Taklimakan desert, Gobi desert, Yongin and Yonago sampling sites. (b) The 3-day back trajectories of the aerosols that arrived at 3,000 m (blue lines) and 1,000 m (red lines) in Yongin, South Korea, and Yonago, Japan, during the three sampling periods; early spring (from 3 March to 14 April), late spring (from 15 April to 19 May), and early summer (from 20 May to 18 June).

 

 

 

Figure 2.

Temporal variations of particles. The figure shows temporal variations of concentrations of organic particles, mineral particles, microbial particles, and black carbon in (a) Yongin, Korea, and (b) Yonago, Japan. Samples were collected at an altitude of 10 m at dust event and non-dust event days between March and June in 2015. Orange areas indicate dust event days.
 

 

Article
Aeolian dispersal of bacteria associated with desert dust and anthropogenic particles over continental and oceanic surfaces

Journal: Journal of Geophysical Research: Atmospheres

Authors: Teruya Maki, Kevin C. Lee, Kei Kawai, Kazunari Onishi, Chun Sang Hong, Yasunori Kurosaki, Masato Shinoda, Kenji Kai, Yasunobu Iwasaka, Stephen D. J. Archer, Donnabella C. Lacap‐Bugler, Hiroshi Hasegawa, Stephen B. Pointing

DOI: 10.1029/2018JD029597

Funder
This study was funded by the Joint Research Program of Arid Land Research Center, Tottori University (grant number 28C2015). This study was supported by the Grant‐in‐Aid for Scientific Research (A) (number 17H01616), (B) (number 18H03385), and (B) (number 26304003), and the Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation (grant number G2702), and the basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (2012R1A1A2042109).