No 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.

Abstract. Aerosol particles, including airborne microorganisms, are transported through the free troposphere from the Asian continental area to the downwind area in East Asia and can influence climate changes, ecosystem dynamics, and human health. However, the variations present in airborne bacterial communities in the free troposphere over downwind areas are poorly understood, and there are few studies that provide an in-depth examination of the effects of long-range transport of aerosols (natural and anthropogenic particles) on bacterial variations. In this study, the vertical distributions of airborne bacterial communities at high altitudes were investigated and the bacterial variations were compared between dust events and non-dust events.

Bioaerosols at high altitudes were collected using an aircraft and a balloon.Pyrosequencing using 16S rDNA revealed vertical distributions of airborne bacteria.16S rDNA clone libraries suggested the transport of terrestrial and marine bacteria.Meteorological conditions contribute to vertical variations in airborne bacteria. 3 AbstractBacterial populations transported from ground environments to the atmosphere get dispersed throughout downwind areas and can influence ecosystem dynamics, human health, and climate change. However, the vertical bacterial distribution in the free troposphere was rarely investigated in detail. We collected aerosols at altitudes of 3,000 m, 1,000 m, and 10 m over the Noto Peninsula, Japan, where the westerly winds carry aerosols from continental and marine areas. During the sampling period on March 10, 2012, the air mass at 3,000 m was transported from the Chinese desert region by the westerly winds, and a boundary layer was formed below 2,000 m. Pyrosequencing targeting 16S rRNA genes (16S rDNA) revealed that the bacterial community at 3,000 m was predominantly composed of terrestrial bacteria, such as Bacillus and Actinobacterium species. In contrast, those at 1,000 m and 10 m included marine bacteria belonging to the classes Cyanobacteria and Alphaproteobacteria. The entire 16S rDNA sequences in the clone libraries were identical to those of the terrestrial and marine bacterial species, which originated from the Chinese desert region and the Sea of Japan, respectively. The origins of air masses and meteorological conditions contribute to vertical variations in the bacterial communities in downwind atmosphere.

No abstract