Abstract
Airborne microorganisms in the upper troposphere and lower stratosphere remain elusive due to a lack of reliable sample collection systems. To address this problem, we designed, installed, and flight-validated a novel Aircraft Bioaerosol Collector (ABC) for NASA's C-20A that can make collections for microbiological research investigations up to altitudes of 13.7 km. Herein we report results from the first set of science flights—four consecutive missions flown over the United States (US) from 30 October to 2 November, 2017. To ascertain how the concentration of airborne bacteria changed across the tropopause, we collected air during aircraft Ascent/Descent (0.3 to 11 km), as well as sustained Cruise altitudes in the lower stratosphere (~12 km). Bioaerosols were captured on DNA-treated gelatinous filters inside a cascade air sampler, then analyzed with molecular and culture-based characterization. Several viable bacterial isolates were recovered from flight altitudes, including Bacillus sp., Micrococcus sp., Arthrobacter sp., and Staphylococcus sp. from Cruise samples and Brachybacterium sp. from Ascent/Descent samples. Using 16S V4 sequencing methods for a culture-independent analysis of bacteria, the average number of total OTUs was 305 for Cruise samples and 276 for Ascent/Descent samples. Some taxa were more abundant in the flight samples than the ground samples, including OTUs from families Lachnospiraceae, Ruminococcaceae and Erysipelotrichaceae as well as the following genera: Clostridium, Mogibacterium, Corynebacterium, Bacteroides, Prevotella, Pseudomonas, and Parabacteroides. Surprisingly, our results revealed a homogeneous distribution of bacteria in the atmosphere up to 12 km. The observation could be due to atmospheric conditions producing similar background aerosols across the western US, as suggested by modeled back trajectories and satellite measurements. However, the influence of aircraft-associated bacterial contaminants could not be fully eliminated and that background signal was reported throughout our dataset. Considering the tremendous engineering challenge of collecting biomass at extreme altitudes where contamination from flight hardware remains an ever-present issue, we note the utility of using the stratosphere as a proving ground for planned life detection missions across the solar system.
Highlights
Microbial “highways” flow naturally overhead in Earth’s atmosphere (Schmale and Ross, 2015) but “traffic patterns” elude the international aerobiology research community due to a widespread shortage of sampling opportunities
Deoxyribonucleic acid (DNA) extraction was performed on each isolate, followed by the polymerase chain reaction (PCR) amplification of 16S ribosomal ribonucleic acid
Our results showed no clear differences in the richness or diversity of airborne bacteria collected at lower altitudes 0.3 to 12 km (Ascent/Descent samples) compared to higher altitudes ∼12.1 km (Cruise samples)
Summary
Microbial “highways” flow naturally overhead in Earth’s atmosphere (Schmale and Ross, 2015) but “traffic patterns” elude the international aerobiology research community due to a widespread shortage of sampling opportunities. Airborne biomass eventually returns to the surface, low sedimentation rates of microorganisms allows potentially long periods aloft in the upper atmosphere and, long distances traveled downwind (Bovallius et al, 2006; Reche et al, 2018). With hundreds of teragrams of microbe-laden dusts from deserts and agricultural soils moving through Earth’s atmosphere each year (Acosta-Martinez et al, 2015), additional surveys are needed to better understand the ecological consequences of airborne biomass exchange, including disease dispersal (Brown and Hovmoller, 2002; Fröhlich-Nowoisky et al, 2016; Mahaffee and Stoll, 2016; Van Leuken et al, 2016). More sampling opportunities above the boundary layer (i.e., >2 km above the Earth’s surface) will improve long range modeling efforts aimed at providing predictive tools for aerobiology studies at regional and global scales (Burrows et al, 2009a,b; Griffin et al, 2017)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.