Live bacteria in atmospheric aqueous droplets are exposed to photooxidants such as hydroxyl radicals (·OH), organic triplet excited states (³C*) and singlet oxygen (¹O₂). These photooxidants are produced from photochemical processes involving organic matter present in atmospheric aqueous droplets. ·OH is the photooxidant known to drive many aqueous photochemical processes. Even though the ·OH photooxidation of organic matter in atmospheric aqueous droplets has been widely studied, equivalent investigations on the ·OH photooxidation of bioaerosols are limited. Little is known about the daytime encounters between ·OH and live bacteria in atmospheric aqueous droplets.

We investigated the aqueous ·OH photooxidation of four bacterial strains in microcosms composed of artificial cloud water that simulated the chemical composition of cloud water in South China. The survival rates for the four bacteria strains decreased to zero within 6 hours during exposure to 1 × 10⁻¹⁶ M of ·OH under artificial sunlight. Bacterial cell damage and lysis released biological and organic compounds, which were subsequently oxidized by ·OH. We used ultrafiltration to separate the water-soluble biological and organic compounds into different molecular weight fractions and found that the molecular weights of some of these biological and organic compounds were larger than 50 kDa. The biological and organic compounds were identified as proteinaceous-like and humic-like components by excitation emission matrix fluorescence spectroscopy with parallel factor analysis. High-resolution mass spectrometry measurements revealed that the O/C, H/C, and N/C elemental ratios increased at the initial onset of photooxidation. As the photooxidation progressed, there were little changes in the H/C and N/C, whereas the O/C continued to increase for hours after all the bacterial cells have died. The increase in the O/C was due to functionalization and fragmentation reactions, which increased the O content and decreased the C content, respectively. We observed that fragmentation reactions played particularly important roles in transforming the biological and organic compounds. These fragmentation reactions cleaved the C-C bonds of carbon backbones of higher molecular weight proteinaceous-like matter to form a variety of lower molecular weight compounds, including humic-like components of molecular weight <3 kDa and highly oxygenated organic compounds of molecular weight <1.2 kDa. We also investigated the propensity of the biological and organic compounds from the bacteria to produce ·OH, ¹O₂, and ³C* upon illumination with artificial sunlight. The steady-state concentrations and quantum yields of the three photooxidants produced varied among the different molecular weight-separated fractions due to the diversity of their chemical composition and optical properties. Using a variety of correlation analysis and machine learning techniques, we identified various chemical and optical parameters that correlated particularly well with the steady-state concentrations or quantum yields of the three photooxidants. Overall, our results provided new insights at the process level on the photooxidation of live bacteria in atmospheric aqueous droplets.

How to cite: Nah, T., Liu, Y., and Lee, P.: Aqueous photooxidation of live bacteria , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2630, https://doi.org/10.5194/egusphere-egu24-2630, 2024.

Airborne microorganisms (bioaerosols), traveling across long distances, can significantly affect ecosystems, biogeochemical cycles, and human health. Dust events are a major source of bioaerosols, contributing to their global dispersion. Due to climate change-driven desertification and land-use changes, these events are projected to increase in intensity and frequency. Therefore, the transport of microorganisms over dust is expected to become more prominent. Hence, it is essential to understand the mechanisms allowing dust-borne microorganisms to survive in their atmospheric journy. Here we will present our findings on the impact of dust origins, meteorological conditions as well as diurnal sampling time on the microbial community composition and bioactivity through high throughput sequencing analysis. Our results show connectivity between bioactive groups. We will also present our findings on the distinctive characteristics of dust-borne prokaryotes isolated from dust events, showcasing diverse spore-forming bacteria with biofilm formation abilities. These findings indicate their possible preferential survival over dust, and open new paths to better understanding the survival strategies of dust-borne microorganisms.

How to cite: Lang-Yona, N.: Dust particles as a supportive environment for biofilm-forming prokaryotes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2684, https://doi.org/10.5194/egusphere-egu24-2684, 2024.

We used sampling of quasi-stagnant radiation fogs in Central Pennsylvania during two years to study the dynamics and microbiology of bacterial assemblages in fog droplets. These microbiomes contain concentrations of bacteria orders of magnitude higher than present in concurrent interstitial aerosols, their concentration depending positively, and unlike chemical solutes, on the fog’s liquid water content and temperature, speaking for the role of in situ growth. Fog water microbiomes are recruited from locally available aerosol bacteria, they are compositionally well-differentiated, and their bacteria display differential cellular traits consistent with an actively growing assemblage. Phylogenetic analyses of bacteria enriched in the droplets suggest that C1-volatile metabolizing heterotrophs constitute the trophic basis of these dynamics. However, major loss factors (wet deposition) export much of the net gains, leaving measurable but only subtle legacies in the aerobiome upon fog dissipation. 

How to cite: Garcia-Pichel, F., Cao, T. T. T., Herckes, P., and Straub, D.: The transient and species-specific microbiome of radiation fog water, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12799, https://doi.org/10.5194/egusphere-egu24-12799, 2024.

Airborne biological material, or bioaerosol, plays an important role in the Earth system and therefore have an impact on the atmosphere, the biosphere and the hydrological cycle as well as on public health. Bioaerosols consist of viruses, bacteria, mold, pollen, plant fibers and fragments that range from tens of nanometers to a few hundred micrometers in size. Terrestrial ecosystems are the major sources of the atmospheric bioaerosols with urban environments and areas with agricultural and industrial activity being particularly important. Desert dust contains high concentrations of bioaerosol mainly composed of soil microorganisms and plant detritus. This dust may be further enriched with fungal spores, bacteria, viruses, and pollen that accumulate as dust plumes are transported over terrestrial and aquatic environment through the adhesion of microbe-laden fine aquatic sprays to dust particles. The relative importance of bioaerosol sources in the atmosphere varies with altitude, season, location and meteorological factors.

In this study, Saharan dust aerosols (n=19) were sampled from East Mediterranean (Crete, Greece) using a high-volume TSPs sampler (TISCH). Dust atmospheric particles were collected on precombusted (450 °C for 5 h) 20 × 25 cm quartz filters (Pall, 2500QAT-UP). The sampling resolution was 48 h, at a flow rate of 85 m³ h⁻¹. We established a reliable analytical protocol for extracting DNA from these Saharan dust particles. Together with biological quantification and identification, chemical analysis was performed, including metals, major ions, phospholipids and sugars.

Results show that the number of Eucaryotic DNA copies were 30 times higher than the bacterial copies during the dust events. The bacterial community composition in the collected dust aerosol as the most abundant Phyla were Proteobacteria (37%) followed by Actinobacteria (22%) and Firmicutes (13%). Furthermore, we analyzed five (n=5) intense dust events using magic angle spinning solid-state ³¹P-NMR. The results show that the typical functional groups in P speciation, were orthophosphate and monophosphate esters which sharing the same chemical shift (H₃PO₄ and RH₂-PO₄), phosphate diesters (R₁R₂ HPO₄) and pyrophosphate (H₄P₂O₇). No phosphonates were detected (C-P bond) in dust samples. Monophosphate esters and diesters are mainly found in nucleotides and their derivatives (e.g., DNA, RNA, AMP, ADP and ATP) but also in phospholipids, and as such, they constitute the majority of atmospheric organic-P. These organic-P compounds have C-O-P bonds and are easily hydrolyzed in the marine environment by alkaline phosphatase enzyme, providing an important source of P in the aquatic ecosystems when Saharan dust is deposited.

How to cite: Violaki, K., Panagiotopoulos, C., Rossi, P., Abboud, E., Kanakidou, M., and Nenes, A.: Microbiome of Saharan dust aerosols, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20130, https://doi.org/10.5194/egusphere-egu24-20130, 2024.

The Arctic region is undergoing rapid environmental changes due to global climate warming. Among the Arctic regions, the surface temperature in the northern Barents Sea, where the Svalbard archipelagos are located, has increased more significantly than in other areas over the last 40 years. This warming results in the loss of sea ice in the ocean and glacier ice in terrestrial areas. These changes in surface conditions may impact the emission of bioaerosols from the Earth's surface, which play a crucial role in ecosystem dynamics and cloud formation. However, there is still limited temporal monitoring in Svalbard and also in entire Arctic. Therefore, in this study, we focus on assessing the temporal changes in bioaerosols during the summer to autumn season in Ny-Ålesund, Svalbard using DNA metabarcoding approaches.

Bioaerosol samples were collected using a vacuum pump with a flow rate of 40 LPM onto HEPA-style filters at the outdoor observatory of the Veksthuset building in Ny-Ålesund. Filters were replaced every 24-72 hours from July to November 2022. Those were then preserved in DNA storage medium (DNA/RNA shield) and transported to the laboratory under frozen conditions. Following particle concentration and DNA extraction, we amplified and sequenced three DNA metabarcoding regions (16S, 18S, and ITS) using the MiSeq platform (Illumina).

Seasonal variations in the observed number of Amplicon Sequence Variants (ASVs) from each barcoding region reveal distinct patterns. These patterns are characterized by elevated ASV counts during the summer (ITS and 18S) and autumn (16S). Microbial communities within the 16S region at the phylum level remain relatively stable throughout the entire season. Conversely, communities within the 18S and ITS regions undergo significant changes in mid-September and after October, coinciding with the terrestrial area being covered by seasonal snowpack. In the presentation, we will provide a more detailed explanation of community changes at the ASV level and discuss the distinctive seasonal patterns observed.

How to cite: Uetake, J. and Tobo, Y.: Difference in seasonal variation between airborne prokaryotic and eukaryotic communities in Ny-Ålesund, Svalbard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10332, https://doi.org/10.5194/egusphere-egu24-10332, 2024.

The phyllosphere is a major source of airborne microorganisms. Some of these microorganisms can act as ice nucleating particles (INPs) and initiate droplet freezing in supercooled clouds. Despite their role in this critical atmospheric process, little is known about the spatiotemporal variations of biological INPs at their source. We investigated this variation on the scale of single (or few) leaves about fortnightly from late summer throughout leaf senescence in two lime (Tilia platyphyllos), beech (Fagus sylvatica), cherry (Prunus avium), and walnut (Juglans regia) trees (n = 2 x 4 x 8 = 64) on a hillside (Gempen, 650 m a.s.l.) in north-western Switzerland. The overall result comprising all species shows an increasing trend in the median cumulative concentration of INPs active at -10 °C (INP_-10) from 4 INPs cm^-2 leaf area at the beginning of August to 38 INPs cm^-2 in mid-November. Further, median INP_-10 concentration was positively correlated with relative humidity throughout the 24 h prior to sampling (Spearman’s r = 0.90, p = 0.005, n = 8). Differential INP spectra between -3 °C to -10 °C displayed clearly defined patterns in 53 of the overall 64 samples. In 28 of these 53 samples (53%), the additional number of INPs activated with every 1 °C step in cooling increased steadily with decreasing temperature. In another 21% we observed a significant peak in the temperature step from -8 °C to -9 °C (i.e., around -8.5 °C), and in further 17% a peak around ‑7.5 °C. Interestingly, these types of spectra were similarly often found in air samples with clearly defined pattern (n = 53) at the high-altitude observatory Jungfraujoch (3580 m a.s.l., Switzerland) in summer 2022 (55% steady increase, 17% peak at -8.5 °C, 21% peak at -7.5 °C). This consistency in spectral pattern supports the notion that forests are a major source of biological INPs affecting atmospheric processes. It also prompts the question which parameter – perhaps leaf wetness duration? – could influence the abundance of biological INPs on both scales, on single leaves as well as in the airshed of a high-altitude observatory.

How to cite: Einbock, A. and Conen, F.: Similar freezing spectra of particles in the phyllosphere as at mixed-phase cloud height, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4172, https://doi.org/10.5194/egusphere-egu24-4172, 2024.

There is growing evidence that the oceans constitute an important source of ice-nucleating particles (INPs) in the atmosphere, aerosolized through sea spray. These particles play a crucial role in cloud formation and cloud properties by inducing ice crystal formation. Microorganisms, in particular, can produce ice-nucleating proteins which are efficient catalysts in the formation of ice, triggering heterogenous freezing between -1°C and -15°C. INPs have been measured in sea bulk water and sea surface microlayer, and specifically Arctic waters have been shown to exhibit ice-nucleation activity at high temperatures. In addition, terrestrial environments have long been recognized as substantial reservoirs of INPs. The runoff from these terrestrial environments, facilitated by meltwater and rivers, could have the potential to contribute a substantial influx of INPs to coastal marine environments. Our understanding of the extent of this input, the properties, and concentrations of INPs, and their connection with the microbial community in sea bulk water and sea surface microlayer remains limited. Furthermore, there is a lack of investigation into the temporal and spatial distribution of INPs in sea water. This information, coupled with atmospheric INP measurements, is needed to improve predictions of INP emissions from the ocean to the atmosphere. Therefore, we conducted a sampling campaign at Disko Island, Greenland, and collected sea bulk water, sea surface microlayer, and air samples from May to September 2023. Freshwater samples were collected from a river in continuation of a marine transect spanning eight km offshore to investigate the impact of terrestrial runoff on the coastal marine microbial community and INPs. Our investigation reveals distinct seasonal variations in INP concentrations, ice-nucleation activity, and microbial community at a regularly visited marine site throughout the sampling campaign. Air samples were collected simultaneously at this marine site, enabling the measurement of INP concentrations and the exploration of the microbial community present in the immediate overlaying air masses. Additional air samples were consistently collected from a foreland, located approximately five km from the marine sampling site, using a high-flow-rate impinger with a specific focus on capturing sea spray emissions and facilitating the integration of the data to the marine water samples. Our results further demonstrate a pronounced input of INPs originating from terrestrial runoff into the sea surface microlayer within coastal marine waters. Notably, this was not observed in the bulk water due to the stratification resulting from the introduction of freshwater. Our study unveils seasonal dynamics of INPs and microbial communities and a prominent impact of terrestrial runoff in Arctic marine waters. The study emphasizes the importance of considering the marine environment as a major source of atmospheric INPs and, further, contributes valuable insights to improve predictions of INP emissions from the ocean to the atmosphere.

How to cite: Castenschiold, C. D. F., Ellebæk, A., Finster, K., and Šantl-Temkiv, T.: Seasonal Dynamics of Arctic Marine Ice-Nucleating Particles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19988, https://doi.org/10.5194/egusphere-egu24-19988, 2024.

Microbes are globally ubiquitous and play a crucial role in ecological network systems and global cycles (e.g., the carbon, nitrogen, water cycles). Hundreds of trillions of microorganisms are estimated to be exchanged between the marine and atmospheric environments, due to the vastness of the sea–air interface. The sea surface microlayer (SML) serves as the interface between the ocean and the atmosphere and is a unique ecosystem for microbial life. The aerosolized microbes may affect ocean ecology, global cycles, and promote genetic exchange between ecosystems. However, little is known about the mechanisms controlling microbial exchange between the environments, and the viable state and metabolic activity of marine bioaerosols. This study aims to characterize the microbial communities of the three environments (surface water-SML-atmosphere) and explore possible linkages between them, by developing a simple and repeatable technique for sampling the SML. We will present the validation of our new SML sampling method, based on surface water sub-sampling, using cell and genomic analyses. This method may provide a substantial improvement compared to direct sampling from the sea, ensuring stabilization without unexpected disturbances. In addition, we will present our results on the linkages between marine, SML and atmospheric microbial communities using our new SML sampling technique, from samples collected in the Pacific Ocean. Our results exhibit different clustering patterns for the three proximal environments, supports their identification as distinct environments with distinct microbial signatures. However, the SML is visualized as an “average” between surface water and air samples both in clustering tightness and location, displays its role as an exchange medium between the ocean water and the marine atmospheric boundary layer. This study contributes to improving understanding of the role of the SML in emission of primary aerosols, leading to better characterization of the ocean-atmosphere interactions and allows for better assessments of their contribution to global cycles and the marine ecosystem.

How to cite: Argaman Meirovich, O. and Lang-Yona, Dr. N.: Sea surface microlayer mediated exchange between the aerobiome and the Pacific Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5231, https://doi.org/10.5194/egusphere-egu24-5231, 2024.

Outdoor viruses from atmospheric ecosystems have rarely been investigated, and thus only a few viral genomes from the air can be found in public databases. Viruses and their hosts have positively correlating guanine-cytosine (GC) contents in their DNA¹. High GC content was previously found in actinobacterial and betaproteobacterial isolates from the stratosphere² as well as in aerosol and rainwater viruses³. This is proposed as an adaptation to harsh environmental conditions, primarily as protection against ultraviolet radiation. Here, we combine metagenomically derived viral operational taxonomic units (vOTUs) collected from aerosols and precipitation samples from the Swedish coast³, along with time-series data collected in Antarctica using different sampling devices. Additionally, cloud water samples from the Puy de Dôme in France⁴ were included. A total of 80 assembled vOTUs, of which 37 were predicted phages, across all samples, had a GC content between 55.2% and 70.3%, considered 'high GC.' Antarctic air vOTUs were found after sampling with the Coriolis µ (wet) but not with the Coriolis Compact (dry) air sampler. The time series indicates overlapping vOTUs between days and sampling height (sea-level or altitude). In Antarctic air, high GC vOTUs (mean GC = 59.6% ± 4.0) were detected on one of the seven days, while low GC viruses were absent in this sample. On other days, the GC of vOTUs was <39%. Thirteen high GC vOTUs from Sweden and Antarctica clustered in a proteomic tree analysis with known high GC phage isolates infecting Microbacterium radiodurans and Arthrobacter sp. (both phylum Actinomycetota). Host predictions using iPHoP revealed that only 11 of the 80 vOTUs could be assigned to bacterial hosts with good confidence, namely to genera Mycobacterium, Ralstonia, Sphingomonas, and Bradyrhizobium. Our results suggest that high GC is a feature in air viruses from different atmospheric sources and latitudes. While these vOTUs occur irregularly at near-ground sampling heights, a high GC content could favor the survival of airborne viruses higher in the troposphere and thus enable infections of extremophilic hosts within air ecosystems.

References:

¹ Simón, D., Cristina, J., & Musto, H. (2021). Nucleotide composition and codon usage across viruses and their respective hosts. Frontiers in Microbiology, 12, 646300.

² Ellington, A. J., Bryan, N. C., Christner, B. C., & Reisch, C. R. (2021). Draft Genome Sequences of Actinobacterial and Betaproteobacterial Strains Isolated from the Stratosphere. Microbiology Resource Announcements, 10(50), e01009-21.

³ Rahlff, J., Esser, S.P., Plewka, J., Heinrichs, M.E., Soares, A., Scarchilli, C., Grigioni, P., Wex, H., Giebel, H.A. and Probst, A.J., 2023. Marine viruses disperse bidirectionally along the natural water cycle. Nature Communications, 14(1), p.6354.

⁴ Dillon, K. P., Correa, F., Judon, C., Sancelme, M., Fennell, D. E., Delort, A. M., & Amato, P. (2020). Cyanobacteria and Algae in Clouds and Rain in the Area of puy de Dôme, Central France. Applied and Environmental Microbiology, 87(1), e01850-20.

How to cite: Rahlff, J., Cockerton, L., Amato, P., Pearce, D. A., and Marz, M.: Appearance of viral genomes with high GC base proportion in atmospheric samples from Europe and Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6162, https://doi.org/10.5194/egusphere-egu24-6162, 2024.

Studies of the impacts of bioaerosol on atmospheric processes often focus on their role in ice nucleation, which is largely determined by their physicochemical properties. Living microorganisms may also play roles in chemical processes by interacting with organics and other molecules, in particular in clouds where condensed water promotes metabolic processes.

Our previous model studies suggest that such biodegradation by living microorganisms may lead to a significant loss of formic and acetic acids in addition to chemical sinks in the atmospheric multiphase system (Nuñez López et al., 2023).

The prior model studies are based on the assumption of a single type of bacteria at fixed number in a small subset of droplets. However, the diversity and abundance of airborne bacteria, and thus their metabolic capabilities, greatly vary with space and time.

Explicitly describing multiple types of bacteria in individual droplet classes within cloud models can become computationally expensive and may be unfeasible to implement in larger-scale models aimed at exploring the role of biodegradation as a sink of organics.

We present different model approaches of varying complexities to explore the conditions under which simplified expressions for the biodegradation of small organic compounds can be applied. This involves the use of averaged biodegradation rates or proxies for representative bacteria species. Box model simulations are performed for airborne bacterial populations of different diversity and abundance, as observed, e.g. in continental or marine scenarios. Our model studies result in recommendations on how to implement biodegradation into atmospheric models of various scales to account for biological sinks of organic compounds and to ultimately constrain atmospheric organic budgets.

Nuñez López, L., Amato, P., and Ervens, B.: Bacteria in clouds biodegrade atmospheric formic and acetic acids, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2270, 2023.

How to cite: Nuñez López, L., Amato, P., and Ervens, B.: Prediction of Biodegradation rates of Atmospheric Organics as a function of bacteria diversity using models of different complexity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1474, https://doi.org/10.5194/egusphere-egu24-1474, 2024.

Primary biological aerosols (bioaerosols) represent the predominant fraction of aerosols within the Amazon rainforest, a global biodiversity hotspot. Bioaerosols encompass a wide range of biological material. These can be single molecules such as proteins, carbohydrates, metabolites, toxins and allergens, or as large as whole dispersal units such as pollen, fungal and cryptogamic spores. They also include whole living or dead microbial organisms such as viruses, bacteria, archaea, or fungi, and fragments or secretions from organism. These bioaerosols can serve as nuclei for ice crystals and cloud droplets and thereby influence the properties of clouds and precipitations patterns with implications for hydrological cycles and the climate. Moreover, the aerial transport of microorganisms contributes to global species spread, with the potential to affect animal, plant, and ecosystem health. Aerosolized soil particles (dust) can act as vehicles, enabling microorganisms to traverse extensive distances, such as the Atlantic Ocean. However, the identity and effects of microorganisms associated with long-range transported dust masses on the local bioaerosol community of the Amazon rainforest is still unknown.

Here, we investigate the effect of dust, originating from the African continent and transported to the Amazon rainforest on the local microbial and fungal bioaerosol community of the Amazon rainforest. We collected total suspended particles at the Amazon Tall Tower Observatory (ATTO) in Brazil before, during and after a dust event, at 42 m and 320 m height. The prokaryotic and fungal communities were analyzed using amplicon sequencing techniques. Our results revealed a distinct local fungal and procaryotic bioaerosol community under dust free conditions. However, dust occurrence did not majorly effect the fungal community structure, which showed an overall very uniform core microbiome, across time and height. In contrast, the prokaryotic community was strongly altered during the dust event, with members of the Bacillota strongly increasing. Also, the prokaryotic core microbiome was smaller compared to the fungal core microbiome and changed between heights. Our findings suggest that the Amazon rainforest air microbiome can be affected by long-range transported dust and the microbial communities transported within while the fungal air microbiome seems overall more stable. Suggesting the transcontinental exchange of dust between Africa and South America as a plausible pathway for the spread of prokaryotes.

How to cite: Weber, J., Barbosa, C., Hrabe de Angelis, I., Yordanova, P., Brill, S., Maier, S., Pöschl, U., Pöhlker, C., and Weber, B.: Long-range transatlantic dust transport: via hitchhiking to South America, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18119, https://doi.org/10.5194/egusphere-egu24-18119, 2024.

Understanding the types of microbes present and their concentrations over time is essential for deciphering the physical, chemical, and biological processes in the atmospheric environment. In this study, Hong Kong, which experiences four distinct seasons, was selected as the study site. High-throughput amplicon sequencing of the 16S rRNA gene was utilized to analyze the microbiomes present, while a light/laser-induced fluorescence (LIF) instrument was employed to characterize the real-time concentrations of fluorescent aerosol particles (FAPs) or bioaerosols. Seasonal variations in the microbiomes were observed, primarily driven by less abundant taxa that were unique to specific locations. Conversely, spatial variations were minimal, suggesting a homogeneity of microbiomes within the scale of a city. The major taxa of the microbiomes reflected the local environments (e.g., aquatic and soil), with neutral assembly processes dominating each season, indicating a minor role of selection in microbial assembly in the air. FAP concentrations were highest in the fall and winter seasons, deviating from measurements in temperate and tropical regions. Bioaerosol concentrations exhibited diurnal patterns, with higher concentrations during the daytime and lower concentrations at nighttime. Certain atmospheric pollutants were associated with bioaerosol concentrations, and positive matrix factorization analysis identified anthropogenic sources as key drivers of bioaerosol concentrations. In summary, the application of molecular techniques and LIF-based instrumentation has provided insights into the microbial composition of the atmospheric environment in a subtropical location, facilitating further investigations into the interactions involving these biological components.

How to cite: Lee, P. K. H. and Miao, Y.: Seasonal Dynamics of the Compositions and Concentrations of Microbiomes in the Atmospheric Environment at a Subtropical Location, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7371, https://doi.org/10.5194/egusphere-egu24-7371, 2024.

The health impacts of air pollution are deeply intertwined with the composition of pollutants, with bioaerosols—microbial particles suspended in the air—playing a critical role. Despite their importance, the behavior of bioaerosols during pollution episodes remainslargely elusive. In this study, we investigated the dynamics of bacterial aerosols over a one-week period. During the sampling period, haze and sandstorm events occurred sequentially, with a transition period in between. Haze air pollution, characterized by high levels of PM_2.5, is a typical form of anthropogenic pollution, whereas sandstorm dust events, characterized by high levels of PM₁₀, are typical natural pollutions. We applied 16S rDNA and 16S rRNA sequencing techniques to explore the total bacterial community and the active bacteria, respectively. Our results revealed distinct bacterial aerosol profiles during haze and sandstorm conditions. Notably, the greatest bacterial diversity was found in sandstorm samples, with the least diversity observed during haze periods. The bacterial aerosols during haze showed the most significant differences compared to those during the transition period, particularly when contrasted with sandstorm samples. The active bacterial profiles, as determined by 16S rRNA sequencing, were found to be dissimilar from the total bacterial communities present during sandstorms. The ecological drivers shaping bacterial community structures also exhibited distinct patterns. Our data suggest that selective forces influence the composition of active bacterial communities in sandstorm samples, as well as the total bacterial population during haze events. A common feature during both haze and sandstorm episodes was the extended residence time of bacteria in the atmosphere, implying that prolonged exposure could alter the structure of airborne bacterial communities. Additionally, our results highlight the increased presence of several pathogens or opportunistic pathogens in the active bacterial communities of sandstorm samples and the total bacteria during haze, indicating a increased health risk for humans, animals, and plants.

How to cite: Shen, F. and Ma, J.: Temporal Dynamics of Bacterial Aerosols in Haze and Sandstorm Events: Implications for Atmospheric Processes and Public Health, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14338, https://doi.org/10.5194/egusphere-egu24-14338, 2024.

Keywords: precipitation, aerosols, microorganisms, Antarctica, clouds

Clouds and precipitation play an intrinsic role in the global climate, upholding the Earth's surface energy equilibrium and water cycle. Despite their significance, clouds and aerosols over Antarctica and the Southern Ocean remain poorly understood, primarily due to the extreme environment for observations and insufficient data. The Antarctic Peninsula (AP) has been exhibiting a significant warming trend over the last 60 years (Jones et al, 2019). Coupled with the rising temperatures, an increase in precipitation and surface melt is being observed across the AP, with major surface melts and precipitation events, both snowfall and rainfall, being associated with atmospheric rivers (ARs) (Gorodetskaya et al., 2023; Wille et al., 2021). ARs are long corridors of intense moisture and heat transport from subtropical and mid-latitude regions poleward, typically also carrying liquid-containing clouds to the AP. Moreover, ARs can impact the long-range transport of aerosols, as well as contribute to gas and aerosol exchange between the atmosphere and the ocean. Aerosols, which serve as cloud condensation and ice nuclei, determine cloud microphysical properties and influence cloud radiative forcing and precipitation formation. Given that a substantial percentage of aerosols are of biological origin, it is crucial to effectively identify and describe them.

In this project, we aim to characterize bioaerosols, specifically microorganisms, present in the precipitation and surface snow in the AP. Rainfall and snowfall samples were collected during PROPOLAR campaigns on King George Island, northern AP, in the vicinity of Escudero and King Sejong stations. The precipitation samples were preserved and analysed using culturable and non-culturable methodologies. Bacterial strains were obtained and identified through 16S rRNA gene sequencing, which provided information about the diversity and phylogenetic relationships of the identified microorganisms. The identified organisms were categorized into six distinct genera, including those recognized for their ice nucleation capabilities, such as the Pseudomonas genus (Attard et al, 2012). The main phylum identified was Proteobacteria. We identified four strains among those analyzed as potentially novel species affiliated with the Spirosoma and Paenibacillus genera. These findings highlight the untapped potential of these regions in harbouring unique microbial biodiversity. 

Obtaining a comprehensive study of the microbial community in precipitation in Antarctica will pave the path to understanding the role these microorganisms have in cloud condensation processes and ice nucleation. More international efforts and campaigns are needed to gain information about aerosols, clouds and precipitation over the Southern Ocean.

Acknowledgements: PROPOLAR (Portuguese Polar Program) projects APMAR/TULIP/ APMAR2 and FCT project MAPS (2022.09201.PTDC)

References: 

Attard et al. 2012. Effects of atmospheric conditions on ice nucleation activity of Pseudomonas.  Atmos. Chem. Phys. https://doi.org/10.5194/acp-12-10667-2012

Gorodetskaya et al. (2023): Record-high Antarctic Peninsula temperatures and surface melt in February 2022: a compound event with an intense atmospheric river. npj Clim.Atmos.Sci. https://doi.org/10.1038/s41612-023-00529-6

Jones et al. (2019). Sixty years of widespread warming in the Southern middle and high latitudes(1957–2016). J.Clim.https://doi.org/10.1175/JCLI-D-18-0565.1 

Wille et al. (2021).  Antarctic atmospheric river climatology and precipitation impacts. J.Geophys.Res.https://doi.org/10.1029/2020JD033788

How to cite: Vučković, K., Lopes, E., Pizarro, L., Semedo, M., de Fátima Carvalho, M., Magalhães, C., and Gorodetskaya, I.: Exploring precipitation over the northern Antarctic Peninsula - a microbiological perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18750, https://doi.org/10.5194/egusphere-egu24-18750, 2024.

The risks of invasions of remote ecosystems by new microorganisms is a major threat as they are likely to impact the diversity and function of resident communities and local ecosystems. In the Antarctic, aerial transport is the primary source of new biological inputs. Airborne communities are believed to be influenced by environmental and climatic conditions, which are already changing rapidly on a global scale, but especially in the Polar regions. Yet, the influence of climate change, weather patterns and environmental conditions on these airborne communities are still unclear. One of the key challenges in understanding these processes is the high heterogeneity and variability of airborne samples. Following the Antarctic Expedition (ACE), in which daily samples were taken around the Antarctic continent to provide spatial distribution of airborne microorganisms, a time series was conducted at one of the ACE field sites (South Georgia) over a period of two weeks, at both high and low altitude to establish the daily variability between aerobiological sample sets. Results showed that although there was indeed a high heterogeneity and variability within the sample sets and across sample types, reliable patterns in the overall diversity could still be determined, and hence single daily samples can still provide useful assessment of aerial diversity over spatial and temporal scales in the Antarctic.

How to cite: Pearce, D., Cockerton, L., Malard, L., Schmale, J., and Convey, P.: SLIDE – Southern Latitudes Island Dispersal Evaluation , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17555, https://doi.org/10.5194/egusphere-egu24-17555, 2024.