Variations in the structure of airborne bacterial communities in a downwind area during an Asian dust (Kosa) event

Abstract

Asian dust (Kosa) events transport airborne microorganisms that significantly impact biological ecosystems, human health, and ice-cloud formation in downwind areas.However, the composition and population dynamics of airborne bacteria have rarely been investigated in downwind areas during Kosa events. In this study, air samplings were sequentially performed at the top of a 10-m high building within the Kosa event arrival area (Kanazawa city, Japan) from May 1 to May 7, 2011, during a Kosa event.The particle concentrations of bacterial cells and mineral particles was ten-fold higher during the Kosa event than on non-Kosa event days. A 16S ribosomal DNA clone library prepared from the air samples primarily contained sequences from three phyla:Cyanobacteria, Firmicutes, and Alphaproteobacteria. The clones from Cyanobacteria were mainly from a marine type of Synechococcus species that was dominant during the first phase of the Kosa event and was continuously detected throughout the Kosa event.The clones from Alphaproteobacteria were mainly detected at the initial and final periods of the Kosa event, and phylogenetic analysis showed that their sequences clustered with those from a marine bacterial clade (the SAR clade) and Sphingomonas spp. During the middle of the Kosa event, the Firmicutes species Bacillus subtilis and Bacillus pumilus were predominant; these species are known to be predominat in the atmosphere above the Chinese desert, which is the source of the dust during Kosa events. The clones obtained after the Kosa event had finished were mainly from Bacillus megaterium, which is thought to originate from local terrestrial areas. Our results suggest that airborne bacterial communities at the ground level in areas affected 2 by Kosa events change their species compositions during a Kosa event toward those containing terrestrial and pelagic bacteria transported from the Sea of Japan and the continental area of China by the Kosa event.

Vertical distribution of airborne bacterial communities in an Asian-dust downwind area, Noto Peninsula

“…3 and 4a). Some clones recovered from the 3 air samples were identical to B. subtilis, which were detected at high altitudes above the Taklamakan Desert (Maki et al, 2008) and were associated with the Asian dust mineral particles collected in downwind areas (Maki et al, 2010;Jeon et al, 2011;Tanaka et al, 2011;Maki et al, 2014;Fig. 4a).…”

“…Species related to B. subtilis were found to be dominant species in the sand samples of the Chinese continental desert and the Antarctic desert (Bottos et al, 2014), and in the air samples collected from the free troposphere during Asian dust events (Smith et al, 2012;Maki et al, 2014). The isolations of Bacillus species were also predominantly obtained from dust samples collected in downwind areas (Hua et al, 2007;Gorbushina et al, 2007).…”

“…The atmosphere is a heterogeneous environment; meteorological shifts and dust events considerably alter bacterial abundance and composition in the Asian atmosphere (Hara and Zhang, 2012;Maki et al, 2014). In addition, airborne microorganisms on North American mountains (2,700 m above sea level) were found to change in response to Asian dust events that included highly diverse bacterial species (Smith et al, 2013).…”

Variations in airborne bacterial communities at high altitudes over the Noto Peninsula (Japan) in response to Asian dust events

“…Epifluorescence microscopy using fluorescent-dye staining is a useful tool for observation and determination of microbial particles in the atmosphere, demonstrating that the biomass of airborne microorganisms increased 10-to 100-fold during Asian dust events (Hara et al, 2012;Maki et al, 2014). Under a fluorescence microscope, DNA in microbial particles fluoresce blue when stained with 4, 6-diamidino-2-phenylindole (DAPI) (Russell et al, 1974), and organic materials aggregated with proteins and microbial cell components were confirmed as yellow fluorescence particles (Mostajir et al, 1995).…”

Abundance and Community Structure of Bacteria on Asian Dust Particles Collected in Beijing, China, during the Asian Dust Season

“…It is well-known that most (usually more than 90%) bacteria in the natural environment are difficult to culture under conventional conditions 23) and thus culture-independent approaches are required for analysis of bacterial dynamics in atmospheric environments. 24,25) In this study, we collected Asian dust particles in Beijing, and visualized bacterial cells on Asian dust particles by laser scanning microscopy to directly demonstrate that Asian dust particles carry bacterial cells. We determined bacterial abundance by quantitative polymerase chain reaction (PCR) targeting the eubacterial 16S ribosomal RNA (rRNA) gene and compared bacterial community profiles by terminal restriction fragment length polymorphism (T-RFLP) among Asian dust samples to investigate inter-seasonal variability of bacterial community structure during the Asian dust season.…”