Intercontinental Dispersal of Bacteria and Archaea by Transpacific Winds

Abstract

f Microorganisms are abundant in the upper atmosphere, particularly downwind of arid regions, where winds can mobilize large amounts of topsoil and dust. However, the challenge of collecting samples from the upper atmosphere and reliance upon culture-based characterization methods have prevented a comprehensive understanding of globally dispersed airborne microbes. In spring 2011 at the Mt. Bachelor Observatory in North America (2.8 km above sea level), we captured enough microbial biomass in two transpacific air plumes to permit a microarray analysis using 16S rRNA genes. Thousands of distinct bacterial taxa spanning a wide range of phyla and surface environments were detected before, during, and after each Asian long-range transport event. Interestingly, the transpacific plumes delivered higher concentrations of taxa already in the background air (particularly Proteobacteria, Actinobacteria, and Firmicutes). While some bacterial families and a few marine archaea appeared for the first and only time during the plumes, the microbial community compositions were similar, despite the unique transport histories of the air masses. It seems plausible, when coupled with atmospheric modeling and chemical analysis, that microbial biogeography can be used to pinpoint the source of intercontinental dust plumes. Given the degree of richness measured in our study, the overall contribution of Asian aerosols to microbial species in North American air warrants additional investigation. A ir samples from the lower troposphere contain a substantial microbial component that originates from a variety of marine/terrestrial sources (1-3). Airborne cells can spread genes to distant environments and even influence weather as cloud/ice condensation nuclei (1), but very little is known about microbial diversity and abundance at higher altitudes, where long-range atmospheric transport (i.e., global dispersal) is more efficient (4). Mountaintop observatories can provide access to the upper troposphere and lower stratosphere, making it feasible to capture enough biomass to employ modern molecular assays. Seasonal measurements at such platforms may help clarify the influence of microorganisms on patterns of climate (5), epidemiology (6-8), and biogeography (9).We collected samples from the Mt. Bachelor Observatory (MBO), a research station 2.8 km above sea level on the summit of an extinct volcano in central Oregon (43.98°N, 121.7°W). In the springtime, windblown plumes of pollution, smoke, and dust from Asia routinely reach the field site after crossing the Pacific Ocean in 7 to 10 days (4, 10, 11). Annually, as much as 64 Tg of Asian aerosols is transported to North America (12). Recently (13), we described two major Asian long-range transport (ALRT) plumes with high concentrations of particulate matter (mostly dust, but also anthropogenic pollution) arriving at MBO. The first event began at 2:00 coordinated universal time (UTC) on 22 April 2011 and lasted 51 h; the second started at 12:00 UTC on 12 May 2011 and ended 80 h later (see Table...

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

“…Chao 1 analysis of the pyrosequencing data showed that the number of bacterial species in the air samples ranged from 270 to 410. In a previous study, microarray analysis detected approximately 400 species in airborne bacterial communities on mountains (Smith et al, 2013), consistent with the estimated numbers observed in this study. In sequential surveys of a mountain site, airborne microbial communities at the higher altitudes of mountains also included highly diverse bacterial populations (Bowers et al, 2012).…”

“…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

“…The westerly winds blowing over East Asia would transport airborne bacteria to the high-altitude atmosphere over the Noto Peninsula and North American mountains (Smith et al, 2013). Our box plots analysis suggested that changes in the bacterial diversity in the dust samples would be more stable than in the non-dust samples (Fig.…”

“…Back trajectories on 19 March 2013 and 20 March 2015 came from the Asian desert region to the Noto Peninsula. Some Bacillus species were predominantly detected at high altitudes above the Taklamakan Desert (Maki et al, 2008) and above downwind areas during Asian dust events (Maki et al, 2010(Maki et al, , 2013Smith et al, 2013;Jeon et al, 2011;Tanaka et al, 2011) (Table 2). Bacillus species are the most prevalent isolates obtained from mineral dust particles collected over downwind areas (Hua et al, 2007;Gorbushina et al, 2007).…”

“…Meteorological shifts and dust events can dramatically alter airborne bacterial communities at high altitudes in Japan (Maki et al, 2013 because of air masses that originate from heterogeneous environments, including marine, mountainous, urban, and desert areas. The airborne microorganisms around North American mountains (2700 m above sea level) were also found to increase their species diversities in response to Asian dust events (Smith et al, 2013). Highthroughput sequencing technology can generate large numbers of nucleotide sequences and the sequencing database has played an important role for investigation of airborne bacterial compositions (Brodie et al, 2007;Woo et al, 2013).…”