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...

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Aim:  To incorporate into the lambda phage genome, a luxI‐based acyl‐homoserine lactone (AHL) synthase genetic construct and exploit the autoamplified power of quorum sensing to translate a phage infection event into a chemical signature detectable by a lux‐based bioluminescent bioreporter, with focus towards facile detection of microbial pathogens. Methods and Results:  The luxI gene from Vibrio fischeri was inserted into the lambda phage genome to construct a model phage‐based biosensor system for the general detection of Escherichia coli. The AHL signalling molecules synthesized upon phage infection are detected by an AHL‐specific bioluminescent bioreporter based on the luxCDABE gene cassette of V. fischeri. The assay generates target‐specific visible light signals with no requisite addition of extraneous substrate. This binary reporter system was able to autonomously respond to lambda phage infection events at target E. coli concentrations ranging from 1 × 108 to 1 CFU ml−1 within 1·5–10·3 h, respectively, in pure culture. When assayed against artificially contaminated lettuce leaf washings, detection within an E. coli inoculum range from 1 × 108 to 130 CFU ml−1 was achieved within 2·6–22·4 h, respectively. Conclusions:  The initial feasibility of binary phage‐based reporter assays indicates that quorum sensing can be used to translate a phage infection event into an autoamplified chemical signature. Significance and Impact of Study:  With further modification, binary phage‐based reporter assays may be capable of rapidly and cost effectively detecting pathogenic agents at very low population densities.

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