Comparison of Bacterial and Fungal Composition and Their Chemical Interaction in Free Tropospheric Air and Snow Over an Entire Winter Season at Mount Sonnblick, Austria

Abstract

We investigated the interactions of air and snow over one entire winter accumulation period as well as the importance of chemical markers in a pristine free-tropospheric environment to explain variation in a microbiological dataset. To overcome the limitations of short term bioaerosol sampling, we sampled the atmosphere continuously onto quartzfiber air filters using a DIGITEL high volume PM10 sampler. The bacterial and fungal communities, sequenced using Illumina MiSeq, as well as the chemical components of the atmosphere were compared to those of a late season snow profile. Results reveal strong dynamics in the composition of bacterial and fungal communities in air and snow. In fall the two compartments were similar, suggesting a strong interaction between them. The overlap diminished as the season progressed due to an evolution within the snowpack throughout winter and spring. Certain bacterial and fungal genera were only detected in air samples, which implies that a distinct air microbiome might exist. These organisms are likely not incorporated in clouds and thus not precipitated or scavenged in snow. Although snow appears to be seeded by the atmosphere, both air and snow showed differing bacterial and fungal communities and chemical composition. Season and alpha diversity were major drivers for microbial variability in snow and air, and only a few chemical markers were identified as important in explaining microbial diversity. Air microbial community variation was more related to chemical markers than snow microbial composition. For air microbial communities Cl − , TC/OC, SO 4 2− , Mg 2+ , and Fe/Al, all compounds related to dust or anthropogenic activities, were identified as related to bacterial variability while dust related Ca 2+ was significant in snow. The only common driver for snow and air was SO 4 2− , a tracer for anthropogenic sources. The occurrence of chemical compounds was coupled with boundary layer injections in the free troposphere (FT). Boundary layer injections also caused the observed variations in community composition and chemistry between the two compartments. Long-term monitoring is required for a more valid insight in post-depositional selection in snow.

Spatial and Annual Variation in Microbial Abundance, Community Composition, and Diversity Associated With Alpine Surface Snow

“…Our estimates of community alpha diversity were in agreement with those observed in previous studies at Jungfraujoch from 2014 (Meola et al, 2015) and 2015 (Wunderlin et al, 2016), and estimates reported for Sonnblick for three consecutive seasons between 2016 and 2017 (Els et al, 2020). In line with our results, communities in these studies contained approximately 50-250 distinct microbial taxa on average, with a similarly low contribution of abundant taxa to the total richness, resulting in low community evenness.…”

“…Microbial communities were composed of similar groups of organisms as have been found in previous studies on mountain surface snow and ice in different parts of the globe (Segawa et al, 2005;Boetius et al, 2015;Maccario et al, 2015;Antony et al, 2016;Carey et al, 2016;Wunderlin et al, 2016;Azzoni et al, 2018;Zhou et al, 2019), including the European Alps (Chuvochina et al, 2011;Meola et al, 2015;Wunderlin et al, 2016;Azzoni et al, 2018;Courville et al, 2020;Els et al, 2020), and >10000year-old Himalayan glacial ice (Zhong et al, 2021). Dominant genera included known psychrophilic or psychrotolerant, UVresistant organisms typical for cryosphere environments such as heterotrophic Polaromonas (Gammaproteobacteria; Darcy et al, 2011) and Hymenobacter (Bacteroidia; Dai et al, 2009;Klassen and Foght, 2011;Sedláček et al, 2019), or photoautotrophs within the Chroococcidiopsidaceae (Cyanobacteria; Baqué et al, 2013).…”

“…The frequency and intensity of this deposition is spatiotemporally variable, for instance depending on the occurrence of dust events, which in turn can result in variation of microbial cell abundances, and cause significant differences in community composition across space and time ( Segawa et al, 2005 ; Chuvochina et al, 2011 ; Meola et al, 2015 ; Els et al, 2019 ; Courville et al, 2020 ). Following deposition, microbial taxa are subject to selection imposed by environmental factors such as high solar radiation as well as low temperatures and nutrient levels, which only allow a certain fraction of the initially deposited taxa to persist and remain active ( Segawa et al, 2005 ; Chuvochina et al, 2011 ; Lopatina et al, 2013 ; Els et al, 2019 , 2020 ; Maccario et al, 2019 ).…”

“…Recording spatiotemporally data is an important step toward achieving this goal. However, so far, studies on microbial communities associated with mountain surface snow and ice have either focused on temporal changes at single locations or small spatial scales ( Segawa et al, 2005 ; Chuvochina et al, 2011 ; Pittino et al, 2018 ; Els et al, 2019 , 2020 ), or differences between locations at single time points ( Wunderlin et al, 2016 ; Azzoni et al, 2018 ; Brown and Jumpponen, 2019 ), whereas data covering both spatial and temporal variation are scarce. As a first initiative to fill this gap, we collected samples across depth profiles of seasonal snowpack at the end of snow accumulation periods in two consecutive years (2015 and 2016) from three mountain summits along a longitudinal transect across the European Alps (i.e., Jungfraujoch, Switzerland; Zugspitze, Germany; Sonnblick, Austria) ( Figure 1 ).…”

Airborne Bacterial Community Composition According to Their Origin in Tenerife, Canary Islands

“…Diversity values obtained were similar or higher than previously reported ( Cáliz et al, 2018 ; Smith et al, 2018 ; Els et al, 2020 ), yet we could not establish a seasonal pattern. Although the summer showed the highest observed diversity, the Shannon index for this season was the lowest, especially within the Izaña sample set, indicating that the bacterial community identified is not evenly distributed.…”