Airborne Bacteria in Earth's Lower Stratosphere Resemble Taxa Detected in the Troposphere: Results From a New NASA Aircraft Bioaerosol Collector (ABC)

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.

Beyond the planetary boundary layer: Bacterial and fungal vertical biogeography at Mount Sonnblick, Austria

“…The driving bacterial classes identified here were repeatedly found in other bioaerosol studies; Bacilli and Cyanobacteria were repeatedly identified with dust storms and long-range troposopheric transport, while Alpha-, Beta-and Gammaproteobacteria as well as Actinobacteria often characterised non-dust below the PBL air (Jeon et al, 2011;Maki et al, 2017;Smith et al, 2010Smith et al, , 2011Smith et al, , 2012Smith et al, , 2018. Some species of Bacilli are frequently detected in connection with dust events, and hence long-distance transport, and are seen as characteristic of Saharan and Chad desert sand events (Favet et al, 2013;Smith et al, 2010Smith et al, , 2012.…”

Impacts of Saharan Dust Intrusions on Bacterial Communities of the Low Troposphere

“…Our results showed that, despite the similitudes in the bacterial diversity between our atmospheric samples and the previously reported ones, there are a number of important and stark differences. For example, we did not find any sequence related to Afipia sp., one of the main constituents of the troposphere community (>40% of total community) reported by DeLeon-Rodriguez et al (2013), as well as some of the most abundant families recently described by Smith et al (2018) in the lower stratosphere (such as Staphylococcaceae, Moraxellaceae, Lachnospiraceae and Ruminococcaceae), although we found a similar number of OTUS. Furthermore, one of the main components found in our samples related to Saharan intrusion, Microvirga sp., has not been reported previously in the consulted literature.…”

Microbial composition in seasonal time series of free tropospheric air and precipitation reveals community separation

“…Studies focusing on free tropospheric air microbial communities often present data from single campaigns or few flights (Schmale and Ross 2015;Techy et al 2010;Jimenez-Sanchez et al 2018;Smith et al 2018;Maki et al 2017;Xia et al 2013;Zweifel et al 2012) and have shown that microbes present in the free troposphere might originate from long-range travel (Maki et al 2017;Smith and David 2012;Smith et al 2011Smith et al , 2012Brown and Hovmøller 2002;Burrows et al 2009a, b). Air masses above and below PBL differ significantly in microbial composition.…”

“…Air masses above and below PBL differ significantly in microbial composition. Free tropospheric habitats tend to have more Firmicutes (Smith et al 2018;, Proteobacteria, Burkholderiales (DeLeon-Rodriguez et al 2013) and extremophile yeasts, Saccharomycetes and Microbotryomycetes (Els et al 2019). While the existence of either a stable (DeLeon-Rodriguez et al 2013) or a highly variable (Zweifel et al 2012) extremophile free tropospheric PBA community is disputed, generally few studies addressing the question were mainly performed over marine and oceanic regions (DeLeon-Rodriguez et al 2013).…”