The Ulaanbaatar region in Mongolia exhibits a characteristic increase in particulate matter (PM) concentrations during spring, due to yellow dust events. This phenomenon has emerged as a significant air pollution issue across Asia. Among air pollution indicators, PM_2.5 has substantial impacts on human health and plays a crucial role in microbial community structures and ecological interactions. This study investigated the characteristics of PM_2.5 microbial communities during spring, including a yellow dust event, in Ulaanbaatar, Mongolia. The bacterial and fungal metagenomes of PM_2.5 samples collected in Ulaanbaatar over a week from April 6 to April 12, 2022 were analyzed. DNA was extracted from PM_2.5 filters, and bacterial 16S rRNA gene regions were amplified using 515F/806R primers. For fungi, ITS2 gene regions were amplified using ITS3/ITS4 primers. Subsequently, sequence analysis was performed using Illumina MiSeq. The study examined the impact of air pollutants (NO_x, NO) and meteorological factors (relative humidity (RH), temperature) on microbial diversity indices (Chao1, Shannon) and the characteristics of dominant species during the investigation period. Based on the sequencing results, the relative abundance of bacteria and fungi in PM_2.5 at the genus level was assessed, and changes in microbial abundance before and after the yellow dust event were compared using a heatmap. Additionally, Spearman correlation analysis was conducted to explore the relationships between the Top 5 dominant bacterial and fungal species on the yellow dust event day and the air pollutants as well as meteorological factors. The results indicated that the diversity indices of bacterial and fungal communities during spring tended to be higher with increasing concentrations of air pollutants and temperature; however, higher RH was associated with lower diversity indices. Changes in dominant microorganisms throughout the study period were confirmed through heatmap analysis, revealing that the composition of dominant microorganisms altered before and after the yellow dust event. On the yellow dust day, the Top 5 dominant bacterial genera were identified as Nitrososphaera, Arthrobacter, Nocardioides, Sphingomonas, and Chthoniobacter, while the Top 5 dominant fungal genera were Trichosporon, Cladosporium, Ascochyta, Alternaria and Vishniacozyma. On the event day, the dominant bacterial genera exhibited positive correlations with PM₁₀ concentrations and temperature, while showing negative correlations with RH. Most of these genera are typically found in soil environments and are known to survive in arid conditions. In the case of fungi, the Top 5 fungal species on the yellow dust day, except for Trichosporon, also showed negative correlations with RH. This study may serve as fundamental data for future management strategies of PM_2.5 air quality.

How to cite: Cho, I., Kang, S., Natsagdorj, A., Lee, J., and Cho, K.-S.: Impact of Yellow Dust Event on PM2.5 Microbial Communities during Spring in Ulaanbaatar, Mongolia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3895, https://doi.org/10.5194/egusphere-egu25-3895, 2025.

Microorganisms in the atmosphere comprise a tiny fraction (~10^-8%) of the Earth’s microbiome. A significant portion of this ‘aeromicrobiome’ consists of bacteria that typically remain airborne for a few days before being returned to the ground through wet or dry deposition. Unlike bacteria in the other Earth surface spheres (e.g., litho-, hydro-, phyllo-, cryospheres), atmospheric bacteria are aerosolized, residing in individual particles and separated by considerable distances (a few centimeters) from each other. Within these small isolated microcosms, bacteria are exposed to particular chemical and physical conditions that potentially affect their stress levels, survival and general functioning. Using fundamental chemical and microphysical concepts of atmospheric aerosol particles and cloud droplets, we examine these specific environmental conditions. In particular, we challenge the concept of clouds as microbial oases by illustrating the water amounts and time scales inside clouds. In addition, we suggest that the small volumes of cloud droplets may cause greater nutrient limitations but simultaneously reduce oxidative stress compared to other aquatic environments. Various chemical and microphysical factors may act as microbial stressors (e.g., oxidative, osmotic, and UV-induced) in the atmosphere, which may either enhance or diminish the survival and diversity of atmospheric bacteria. Based on established atmospheric chemical and microphysical principles, we discuss that observed trends of bacterial community properties and pollutant concentrations may lead to incorrect interpretations due to confounding factors. In summary, our presentation aims to motivate future experimental and modeling studies to disentangle the complex interplay of chemical and microphysical factors with the atmospheric microbiome. Such studies are important to eventually allow for a comprehensive understanding of the atmosphere’s role in affecting airborne microorganisms, a small yet rapidly evolving component of the Earth’s microbiome.

Ervens, B., Amato, P., Aregahegn, K., Joly, M., Khaled, A., Labed-Veydert, T., Mathonat, F., Nuñez López, L., Péguilhan, R., and Zhang, M.: Ideas and perspectives: Microorganisms in the air through the lenses of atmospheric chemistry and microphysics, Biogeosciences, 22, 243–256, https://doi.org/10.5194/bg-22-243-2025, 2025.

How to cite: Ervens, B., Amato, P., Aregahegn, K., Joly, M., Khaled, A., Labed-Veydert, T., Mathonat, F., Nuñez-López, L., Peguilhan, R., and Zhang, M.: Microorganisms in the air through the lenses of atmospheric chemistry and microphysics , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17716, https://doi.org/10.5194/egusphere-egu25-17716, 2025.

Fungi are among the most important biota on the planet, mediating ecosystem processes and contributing to the global bioaerosol budget and pollution even when metabolically inactive. Despite this, diversity and transport of fungi in the atmosphere are poorly explored. Here I show that the atmosphere contains diverse fungi with varied ecological roles and recruitment reflecting underlying habitats. The atmospheric mycobiome is dominated by decomposers and pathogens; over 40% of the total airborne mycobiota are known pathogens of plants or animals, including humans, with the capacity to transfer antibiotic resistance genes. Using aircraft surveys between 2022-2023 and unprecedented comprehensive environmental datasets, I found that remote sensing and meteorological data can predict diversity of fungi comprising the rare/transient portion of the atmospheric mycobiome. Vegetative decay/turnover is linked to increased fungal richness in the atmosphere, strengthening the view that phenology is a major determinant of atmospheric biodiversity. Additionally, ecological selection and niche effects can shape vertical assembly of the atmospheric mycobiome. Forward trajectory models predict air masses carrying the sampled fungi will reach Africa, Europe, and Asia as far as east as Kazakhstan, with global impacts and long-range transport beyond 11,000-km possible. This work sheds light on how genomic and environmental datasets acquired by aircraft and satellites can be used for multipronged data forecasts and dispersal predictions to allow proactive measures, clarify aerobiology questions, and provide a unified view of fungal ecology for planetary protection.

How to cite: Metris, K.: Fungus above us: Eco-environmental drivers of fungal diversity and transport in the atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2599, https://doi.org/10.5194/egusphere-egu25-2599, 2025.

Whiteface Mountain (WFM) in northern NY State is the site of a historic mountaintop atmospheric observatory with an ongoing cloud water chemistry monitoring program that has been operating every summer (June through September) since 1994. Though long-term chemical analysis has been conducted, no analysis on the microbiome has been completed at WFM. Over the years, a new chemical regime has been reported in the cloudwater with missing analytes. Knowing how microbes can interact with chemicals, we hypothesize microbes are partially responsible for this shift and are crucial in understanding the chemical background of clouds.

To start this study, cloudwater filters have been analyzed both chemically and microbially. Chemically, weighted averages have been calculated for each cloudwater filter based on the chemical composition of the clouds. Microbially, we have begun DNA extractions and subsequent metagenomic analysis using the Oxford Nanopore MinION using a select number of cloud water filters from 2024. Overall, this study aims to build upon microbial work accomplished by the Puy de Dôme groups and discuss the collection, storage, and analysis of cloudwater filters to connect the chemical to the microbial at WFM.

How to cite: Lombardo, S., Tripathy, A., Chittur, S. V., Gentry, D., Hayden, A., Kuentzel, M. L., Casson, P. W., Patel, R., Hammond, L., and Lance, S.: Preliminary study of Microbiology in Clouds at Whiteface Mountain in New York, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7510, https://doi.org/10.5194/egusphere-egu25-7510, 2025.

Long-range atmospheric processes facilitate global dispersal of microorganisms, with significant implications for Earth’s ecosystems functioning and global health. While traditional aerobiological studies have focused on low troposphere aerosols, assuming airborne communities are primarily influenced by neighbouring ecosystems, our study challenges this perspective. We analysed nearly three decades of aerosol particles present in rainwater samples collected at a mountain site located in South Europe (Iberian Peninsula, NE Spain). Coupling this data with analyses of high troposphere air mass provenances and genetic data of topsoils from North Africa and from a global public bacterial database, we revel a persistent influence of desert microorganisms from North Africa in Southern European sky. Remarkably, desert-derived microorganisms dominate even in rain originating from the Atlantic Ocean, despite sea spray being the largest source of global aerosols. The frequency of dust outbreaks, altitude reached, and long residence times of fine-sized particulates are postulated as critical factors that significantly shape the long-range and persistence of aerial assemblages, while air mass provenance playing a secondary role. Our findings highlight the profound and long-lasting impact of desert aerosols on terrestrial ecosystems, calling for further exploration of intercontinental aerial connections with deserts and drylands elsewhere, and the ecological implications of desert immigrants on worldwide ecosystems.

How to cite: Cáliz, J., Menéndez-Serra, M., Triadó-Margarit, X., Avila, A., and O. Casamayor, E.: Microorganisms from North African deserts persist in Southern Europe’s atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18628, https://doi.org/10.5194/egusphere-egu25-18628, 2025.

Introduction:

High-altitude snowy regions are recognized as unique biomes hosting diverse microbial communities. Microorganisms in these environments have evolved adaptations to survive extreme conditions, such as low temperatures, high UV radiation, and limited nutrient availability. These adaptations may include antibiotic resistance and virulence factors, which could pose ecological and public health risks if transferred to human pathogens or clinically relevant ecosystems. 

This study aimed to isolate and identify bacterial strains from these environments, assess their temperature tolerance, hemolytic activity, and potential antibiotic resistance profiles and to investigate the presence of antibiotic resistance genes (ARGs) and their potential public health risks.

Methods:

Snow samples were collected from Chamrousse Ski Resort (Grenoble, France) and cultivated on R2A agar at 4°C, 15°C, and 37°C, with morphologically distinct colonies isolated and purified. Growth was monitored over 7 days at 4°C, 15°C, 25°C, and 37°C by measuring OD600 at 24-hour intervals to assess temperature tolerance. Hemolytic activity was evaluated on sheep and horse blood agar plates incubated at 15°C, 25°C, and 37°C, with patterns of alpha, beta, or gamma hemolysis recorded. Genomic DNA was extracted, and 16S rRNA sequencing was used to identify the isolates at the species level. Whole genome sequencing was conducted using the Oxford Nanopore method, and antibiotic resistance genes (ARGs) were identified via the CARD database. Minimum inhibitory concentration (MIC) testing is planned as a follow-up to validate resistance profiles and assess the functional expression of the identified ARGs.

Results:

Sanger sequencing of the 16S rRNA gene identified Peribacillus simplex for isolates 1, 2, and 3, and Sphingomonas faeni for isolate 4, with 100% sequence homology. Growth monitoring revealed that Peribacillus isolates grew best at 25°C, with Peribacillus 1 showing moderate growth at 37°C, while Sphingomonas exhibited psychrotolerant traits, thriving at 15°C and 25°C but performing poorly at other temperatures. Hemolytic activity tests showed that Peribacillus 1 exhibited alpha hemolysis on both sheep and horse blood agar, whereas Peribacillus 2 and 3 showed gamma hemolysis, and Sphingomonas did not grow on blood agar. Whole genome sequencing identified several antibiotic resistance genes (ARGs) linked to multidrug resistance and virulence, including blaZ and vanY in Peribacillus spp., and acrB and mexA in Sphingomonas spp.

Conclusion:

This study highlights the adaptability of microbial communities in snowy alpine environments to changing climates and their potential to spread ARGs and hemolytic features into ecosystems. The presence of such traits in these microorganisms underscores their possible role as reservoirs of antibiotic resistance and virulence factors in natural habitats. Further studies, including MIC testing and pathogenicity assessments, are crucial to fully understanding the ecological and public health implications of these findings.

How to cite: Kashiri, M., Zervas, A., H. H. Brill, F., Steinmann, J., and M. Anesio, A.: Isolation and characterization of potentially pathogenic bacteria from mountainous regions in France, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16671, https://doi.org/10.5194/egusphere-egu25-16671, 2025.

Clouds have been regarded as atmospheric oasis for microbes including psychrophilic bacteria (Delort et al., 2017; Péguilhan et al., 2023). However, adaptations of bacteria to the cloud environment and interactions with viruses are not fully understood. In this study, cloudwater was sampled with six compact Caltech active strand cloud water collectors (Demoz et al., 1996) on the Mount Verde, a mountain of 744 m height on the São Vicente island in the tropical Atlantic Ocean (van Pinxteren et al., 2020) and stored frozen. From iron-flocculated and filtered cloudwater samples, DNA was short-read sequenced for metagenomics, and 24 bacteria were additionally isolated from these samples on Luria-Bertani (LB) and Reasoner's 2A (R2A) agar. After purification, the bacterial DNA was subjected to whole-genome sequencing, revealing a diverse array of microbial taxa. The isolate genomes were identified as belonging to Gram-positive species, including Agrococcus sp., Alkalihalobacillus_A gibsonii_A, Arthrobacter sp., Bacillus spizizenii, Cytobacillus oceanisediminis, Curtobacterium spp., Deinococcus sp., Micrococcus luteus, and Rossellomorea spp., as well as Gram-negative species such as Paracoccus marcusii, and Sphingomonas sp. This microbial diversity highlights the presence of spore-forming, halotolerant, and marine-associated bacteria in cloudwater. The genomes had an average GC content of 58.3% (range 41% – 73%) and encoded for cold-shock genes probably supporting survival during sample freezing and in supercooled cloudwater. The presence of 24 prophages and a diverse arsenal of antiviral defense systems, including adaptive CRISPR immunity targeting viral operational taxonomic units (vOTUs), indicates ongoing bacterial-viral interactions in cloudwater. On average, bacterial strains encoded for five defense systems, with restriction-modification systems being the most common. Interestingly, the isolated strain Sphingomonas sp. MPC37 encoded for the highest number of defense systems (12), indicating its potential ecological significance in this unique environment. Metagenomic sequencing identified 458 vOTUs, with major bacterial hosts predicted as Sphingomonas spp. (75 vOTUs), Deinococcus spp. (15), Novosphingobium spp. (14), and Methylobacterium spp. (13). Analysis of air mass trajectories for the cloudwater suggests a marine origin for certain samples, which were associated with the highest counts of both unique and total vOTUs. We also find genetic variability within a population of closely related viruses (microdiversity). Viral variants arise sequentially during different cloud events and are shared among temporally proximate events. Our results reveal clouds as dynamic microbial and viral ecosystems with complex survival strategies and interactions.

References

Delort, A. M., Vaïtilingom, M., Joly, M., … & Deguillaume, L. (2017). Clouds: a transient and stressing habitat for microorganisms. Microbial ecology of extreme environments, 215-245. https://doi.org/10.1007/978-3-319-51686-8_10

Demoz, B. B., Collett, J. L., & Daube, B. C. (1996). On the Caltech Active Strand Cloudwater Collectors. Atmospheric Research, 41(1), 47-62. https://doi.org/10.1016/0169-8095(95)00044-5

Péguilhan, R., Rossi, F., Joly, M., … & Amato, P. (2023). Clouds, oases for airborne microbes – Differential metagenomics/ metatranscriptomics analyses of cloudy and clear atmospheric situations. bioRxiv, 2023.2012.2014.571671. https://doi.org/10.1101/2023.12.14.571671

van Pinxteren, M., Fomba, K. W., Triesch, N., . . . & Herrmann, H. (2020). Marine organic matter in the remote environment of the Cape Verde islands – an introduction and overview to the MarParCloud campaign. Atmos. Chem. Phys., 20(11), 6921-6951. https://doi.org/10.5194/acp-20-6921-2020

How to cite: Rahlff, J., Das, R., Büschel, R., Micheel, J., and van Pinxteren, M.: Hidden Ecosystems Above: Unraveling Viral-Bacterial Interactions in Cloudwater, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1548, https://doi.org/10.5194/egusphere-egu25-1548, 2025.

Primary Biological Aerosols (PBAPs) or bioaerosols are airborne particles originating from biological sources that are directly emitted from the biosphere into the atmosphere. These include bacteria, archaea, viruses, pollen, fungal spores, and fragments of plants and animals (Després, 2012) PBAPs play a significant role in atmospheric processes, climate regulation, and human health, making it essential to investigate their sources, composition, and emission mechanisms.

Bioaerosols can be transported over short or long distances, influenced by factors such as atmospheric turbulence, and environmental conditions (Fröhlich-Nowoisky, 2016) However, the mixing of locally emitted particles with those transported over long distances complicates the accurate identification of their emission sources. This challenge hinders our ability to fully understand their real influence on the atmosphere and ecosystem of origin.

To better elucidate the exchange of particles between these interconnected systems, in this study we investigated the plant and soil litter composition of a temperate floodplain forest thanks to the Leipzig Canopy Crane facility, located in the Leipzig Auwald, along with the dynamics of bioparticles in the air between the spring and autumn seasons.

Relevant data were obtained through sequencing the samples. By comparing the sequences with their potential sources, we obtained temporal and source-specific variations in the bioaerosol community structure across the different months. In Bacteria there is an increase in the overall diversity from spring to autumn, similar seasonal variation is observed in the fungal population. Ascomycota, one of the more dominant groups in the microbial community, varies in abundance with seasonal shifts, being consistently more abundant in the air samples when compared to Basidiomycota which are more prevalent in source communities, likely contributed by their individual dispersion properties.

References-

• Després, V. R., Huffman, J., et al. (2012). Primary biological aerosol particles in the atmosphere: A review. Tellus B: Chemical and Physical Meteorology, 64(0), 15598. https://doi.org/10.3402/tellusb.v64i0.15598
• Fröhlich-Nowoisky, J., et al. (2016). Bioaerosols in the Earth system: Climate, health, and ecosystem interactions. Atmospheric Research, 182, 346–376. https://doi.org/10.1016/j.atmosres.2016.07.018

How to cite: Valath Bhuan Das, B., Herrmann, M., Michalzik, B., Dunker, S., and Sánchez-Parra, B.: In-depth analysis of the origin of Primary Biological Aerosol Particles in a temperate forest of Leipzig, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11035, https://doi.org/10.5194/egusphere-egu25-11035, 2025.

The atmospheric dust cycle serves as a global conduit for microorganisms, with implications for environmental processes, ecosystem health, and human well-being. This study investigates the growth dynamics of dust-borne bacteria, focusing on their ability to thrive on atmospheric dust substrates, the characterization of the microbiome, their localization, and interactions. Dust samples collected from the eastern Mediterranean were cultured to identify selected bacterial with versatile metabolic capacities that are often associated with significant ecological and health impacts. We will present our findings of their growth patterns, substrate utilization, and environmental tolerance, explored under laboratory conditions. Our preliminary findings highlight the diversity of dust-borne bacterial community, their potential interactions, and their durability in different environmental conditions and anthropogenic effects.

How to cite: Lahav, E. and Lang-Yona, N.: Growth Dynamics of Dust-Borne Bacteria on Atmospheric Dust Substrates and Potential Implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19919, https://doi.org/10.5194/egusphere-egu25-19919, 2025.

How to cite: Mascitelli, A., Chiacchiaretta, P., Prestileo, F., Stella, E. M., Aruffo, E., Simeone, P., Lanuti, P., Di Lodovico, S., Di Giulio, M., Guarnieri, S., Del Boccio, P., Cufaro, M. C., Gatta, V., Anaclerio, F., Dietrich, S., and Di Carlo, P.:  Cyanobacteria and climate change: Insights from Atmospheric and Heritage Studies , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1414, https://doi.org/10.5194/egusphere-egu25-1414, 2025.

Lipidomics, a subfield of metabolomics, is an emerging field where hundreds to thousands of lipid species are simultaneously identified. Given the ubiquity and diverse biological roles of lipids, lipidomics offers valuable insights into mechanisms and the discovery of biomarkers related to environmental stressors that affect the cellular physiology and their numerous biochemical pathways. The major source of lipids in the atmosphere are the biogenic particles (bioaerosols) e.g., bacteria, fungi, pollen, plant fragments and viruses. Specifically, the terrestrial ecosystems including deserts, are the major sources of the atmospheric bioaerosols with urban environments and areas with agricultural and industrial activity being particularly important. The desert dust aerosols contain high concentrations of bioaerosols mainly composed of soil microorganisms and plant detritus. Agricultural dust can contain significantly more amounts of biological material, which subsequently can be enriched with additional biogenic particles when they are transported across terrestrial and aquatic environment through their coagulation with other airborne bioaerosols. The lipidome of airborne biogenic particles is unexplored to date, yet it can provide unique insights on bioaerosols, their stress state and oxidant exposure history. During this study we used lipidomics as a novel tool for the atmospheric research, to study the lipid changes in bioaerosols systems induced by their exposure to air pollutants and other atmospheric aging factors.

To achieve this, Saharan dust aerosols (n= 15) were sampled from East Mediterranean (Crete, Greece) using a high-volume (85 m³ h⁻¹) TSPs sampler (TISCH). Dust atmospheric particles were collected on precombusted (450 °C for 5 h) 20 × 25 cm quartz filters (Pall, 2500QAT-UP). A reliable analytical protocol was established for lipidomics analysis of Saharan dust aerosols, which allowed us to identify approximately 60 lipid species, primarily phosphatidylcholines (PC), phosphatidylethanolamines (PE), triglycerides (TG), and their oxidation products, ceramides (Cer), and monogalactosyldiacylglycerols (MGDG). In addition to lipid analysis, biological identification and chemical analysis, including metals, major ions, and sugars, was also performed and will be discussed in detail.

Each dust event has a distinct signature, reflecting not only the chemical composition of the Saharan soil but also the atmospheric processing during its long-range transport. Preliminary results indicate a higher percentage contribution from the oxidation products of TG (OxTG, 33%) and PCs (OxPC, 22%) to the total identified lipids. The significant correlation between PCs and mannitol indicates a fungal contribution to airborne cholines. Furthermore, the correlation between anthropogenic metals (e.g., V, Ni, As, Cr, Pb) and galactolipids (MGDG), which are common plant membrane lipids, indicates a complex mixture of anthropogenic emissions and plant material in the dust aerosols due to long range transport of Saharan soil.

How to cite: Violaki, K., Panagiotopoulos, C., Rossi, P., Abboud, E., Kanakidou, M., Evangeliou, N., Groot Zwaaftink, C., and Nenes, A.: Lipidome of Saharan dust aerosols, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15888, https://doi.org/10.5194/egusphere-egu25-15888, 2025.

Pseudomonas syringae is a common plant pathogen, posing significant threats to the global crop production. By producing ice-nucleating proteins (INpro), encoded by the inaZ gene, cells can inflict frost injuries to plants, gaining access to nutrient-rich plant tissue. Furthermore, P. syringae can impact cloud formation and interfere with atmospheric chemistry through their metabolic and ice-nucleation activity. Both metabolic activity and inaZ gene expression under atmospheric conditions remain poorly understood, limiting our ability to accurately predict the atmospheric impact and dispersal success of P. syringae.

Our fist aim was to investigate the metabolic activity of P. syringae at simulated atmospheric conditions. We exposed single cells placed on polycarbonate filters to RH 94-100% in presence of D₂O. We used the incorporation of deuterium as an activity marker detected via nanoscale secondary ion mass spectrometry (NanoSIMS). Cells exhibited metabolic activity when liquid water was available (RH 100%) without the addition of carbon sources, suggesting that P. syringae can maintain activity based on storage compounds. While we observed a significant decrease in deuterium incoorporation when water was supplied through the vapor phase (<100% RH), likely due to reduced viability, a fraction of cells remained metabolically active at 97% and 94% RH. Interestingly, we observed deuterium incorporation in non-viable cells, likely because of residual enzymatic activity. Such residual enzymatic activity in dead airborne cells may have unknown impacts on atmospheric chemistry, which remain to be determined. Altogether, the results suggest that metabolic activity is possible both in cloud droplets and in dry atmosphere based on storage compounds available in cells, which could support cells in actively modifying their surface properties, by e.g. synthesizing novel INpro while airborne.

Our second aim was to investigate the effect of aerosolization on the inaZ gene expression in P. syringae. Using bubble-bursting aerosolization combined with immunofluorescence staining we found a significantly larger proportion of INpro-bearing cells in the aerosolized fraction (33.2%) compared to pre-aerosolization (10.7%). Using microbial adhesion to hydrocarbon test in combination with a droplet-freezing assay to quantify INpro-bearing cells, we found that cell surface hydrophobicity did not vary between INpro-bearing and other cells, suggesting that our observation was not linked to preferential aerosolization of INpro-bearing cells. Finally, we assessed the relation between cell viability and the number of INpro-bearing cells, to decipher whether INpro synthesis is triggered in aerosolized cells. Here, cells were aerosolized using a Sparging Liquid Aerosol Generator into a flow tube at varying RH and were recollected using different methods which both affected cell viability. Viability was determined by live/dead staining and flow cytometry. We found that the increase in INpro-bearing cell fraction after aerosolization, as determined via the droplet-freezing assay, correlated with the fraction of viable cells, suggesting that a stress response triggered inaZ gene expression leading to the synthesis of novel INpro.

Overall, we demonstrated that metabolic activity and inaZ gene expression is feasible in airborne P. syringae and leads to a significant increase in INpro-bearing cells. These processes may have profound impacts on cloud formation,  atmospheric chemistry, and the dispersal success of P. syringae.

How to cite: Šantl-Temkiv, T., Wieber, C., Sánchez, M. P., Legin, A., Schintlmeister, A., Imminger, S., Christiansen, S., Ling, M., Isaksen, A. K., Bilde, M., Boesen, T., Woebken, D., Rosati, B., and Finster, K.: Metabolic activity and inaZ gene expression during atmospheric dispersal of plant pathogen Pseudomonas syringae , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19389, https://doi.org/10.5194/egusphere-egu25-19389, 2025.

The atmosphere harbors a great diversity of microorganisms. Among them, some taxa of bacteria, such as Methylobacterium species are abundant and recurring members of the viable fraction (Amato et al., 2017; Woo and Yamamoto, 2020). These include non-obligate light-users, and we postulate that this function could be linked with their prevalence and survival capacity in the atmosphere. The alternative use of light to generate biochemical energy (ATP) through photoheterotrophy and anoxygenic photosynthesis is known to enhance survival under nutrient-deficient conditions (Soora and Cypionka, 2013). The use of light could therefore be beneficial and favor survival by supporting the maintenance of metabolic activity in the atmospheric environment,  with dispersed droplets or particles where access to substrates is limited.

To test the hypothesis that photoheterotrophy is beneficial to the survival of airborne bacteria, two distinct phenotypes of the same strain (with or without the photosynthetic pigment bacteriochlorophyll; [BChl+] or [BChl-], respectively, which can be controlled by growing cells under dark or light conditions, respectively) of a facultative photoheterotrophic strain of Methylobacterium sp. (R17b-9), isolated from clouds, were injected into the atmospheric simulation chamber (ASC) "ChAMBRe" (Vernocchi et al., 2023). Their survival was monitored for 2 hours while being exposed to different light intensities. During experimentation in the ASC, cell viability, cultivability, ATP concentration and residence time were measured.

Bacteria containing bacteriochlorophyll retained greater viability and cultivability than those lacking this photosynthetic pigment.  Light exposure on [BChl-] phenotype had a negative impact on cultivability, but not on viability. The mean half-lives (measuring by cultures) of bacteria [BChl-] was ~100-700 min depending on light intensity whereas there was no loss of cultivability over time for bacteria with pigment independently from light exposure. The ATP/cell ratio was 3 times greater for bacteria with bacteriochlorophyll than without. In addition, bacteria with bacteriochlorophyll sedimented 1.71 times faster than their counterparts without the pigment. This study supports the idea that not all bacteria are equal to atmospheric transport, and that specific phenotypic traits can be involved. It is possible that the widespread distribution, at low level, of photoheterotrophy in bacteria in the global environment could be promoted by their increased ability to disperse aerially.

Reference

Amato, P., Joly, M., Besaury, L., Oudart, A., Taib, N., Moné, A. I., Deguillaume, L., Delort, A.-M., and Debroas, D.: Active microorganisms thrive among extremely diverse communities in cloud water, PLOS ONE, 12, e0182869, https://doi.org/10.1371/journal.pone.0182869, 2017.

Soora, M. and Cypionka, H.: Light Enhances Survival of Dinoroseobacter shibae during Long-Term Starvation, PLOS ONE, 8, e83960, https://doi.org/10.1371/journal.pone.0083960, 2013.

Vernocchi, V., Abd El, E., Brunoldi, M., Danelli, S. G., Gatta, E., Isolabella, T., Mazzei, F., Parodi, F., Prati, P., and Massabò, D.: Airborne bacteria viability and air quality: a protocol to quantitatively investigate the possible correlation by an atmospheric simulation chamber, Atmospheric Measurement Techniques, 16, 5479–5493, https://doi.org/10.5194/amt-16-5479-2023, 2023.

Woo, C. and Yamamoto, N.: Falling bacterial communities from the atmosphere, Environmental Microbiome, 15, 22, https://doi.org/10.1186/s40793-020-00369-4, 2020.

How to cite: Mathonat, F., Mazzei, F., Prévot, M., Vernocchi, V., Gatta, E., Joly, M., Théveniot, M., Ervens, B., and Amato, P.: Photoheterotrophy provides increased fitness in airborne bacteria: Aerosol simulation chamber studies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6447, https://doi.org/10.5194/egusphere-egu25-6447, 2025.

Transboundary movement of atmospheric microorganisms through dust transportation plays a pivotal role in influencing human health, agricultural productivity, and climate dynamics by participating in cloud condensation processes. Present study investigates long-range transported atmospheric bacteria along with dust particlesover Darjeeling (27°03′N, 88°26′E), a high-altitude region (2.2 km amsl) in the Eastern Himalayas, India. 27 samples are collected in winter (Temp: 6.2± 1.5°C; RH: 85.2 ± 9.6%) and summer 2022 (Temp: 16 ± 1.5°C; RH: 93.5 ± 6.5%). Total bacterial cell count is found tobe increased by 24 ± 0.4% in summer compared to that in winter. Concurrently, particle number concentrations, measured using a Scanning Mobility Particle Sizer (SMPS) within the size range of 8-350 nm, showed 70% increasein summer, with modal size shifting from 110 nm to 150 nm.Satellite observations from MODIS on-board Aqua, Terra, and OMI on-board Aura reveal an increase in Aerosol Optical Depth (AOD) from 0.4 in winter to 0.7 in summer, alongside decline in Angstrom Exponent from 1.6 to 0.3, indication of coarser aerosol abundances. Aerosol Index also rises from 0.8 to 2.1, indicating dust dominance. CALIPSO data identifies a 1 km thick dust layer within 2 to 3 km altitude above the Eastern Himalayas. Air mass back-trajectory analysis suggests dust particles travel at an altitude of 2 to 3 km from the Thar Desert to Eastern Himalayas.Seasonal shifts in microbial communities are evident, with higher Shannon diversity in summer (4.4 ± 0.8) compared to winter (2.3 ± 0.6). Beta diversity analyses confirm distinct community compositions in summer that is due to transport of unique bacteria attached with desert dust. In summer, predominant bacterial genera included Flavobacterium (5.4 ± 3.6%), Nocardioides (4.2 ± 3%), and Corynebacterium (4.2 ± 1.4%), while Corynebacterium (2.4 ± 0.5%), Acinetobacter (1.8 ± 0.9%), and Massilia (1.3 ± 0.3%) in winter. Notably, pathogenic genera such as Afipia and Clostridium, linked to human and animal infections, are detected with dust exclusively in summer.Presentresult highlights the role of transported dust-associated microbes in altering the airborne bacterial composition in the Himalayas, providing critical insights into the sources and biodiversity changes over the Eastern Himalayas in India.

How to cite: Pramanick, A., Saikh, S. R., Mushtaque, M. A., and Das, S. K.: Study on long-range transport of dust-associated airborne bacteria over Eastern Himalayas in India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1069, https://doi.org/10.5194/egusphere-egu25-1069, 2025.