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A cloud water sample collected at the puy de Dôme observatory (PUY) has been incubated under dark conditions, with its endogenous microbiota at two different temperatures (5 and 15 °C), and the change in the molecular organic composition of this sample was analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Microorganisms were metabolically active and strongly modified the dissolved organic matter since they were able to form and consume many compounds. Using Venn diagrams, four fractions of compounds were identified: (1) compounds consumed by microbial activity; (2) compounds not transformed during incubation; (3) compounds resulting from dark chemistry (i.e., hydrolysis and Fenton reactions) and, finally, (4) compounds resulting from microbial metabolic activity. At 15 °C, microorganisms were able to consume 58% of the compounds initially present and produce 266 new compounds. For this cloud sample, the impact of dark chemistry was negligible. Decreasing the temperature to 5 °C led to the more efficient degradation of organic compounds (1716 compounds vs. 1094 at 15 °C) but with the less important production of new ones (173). These transformations were analyzed using a division into classes based on the O/C and H/C ratios: lipid-like compounds, aliphatic/peptide-like compounds, carboxylic-rich alicyclic molecule (CRAM)-like structures, carbohydrate-like compounds, unsaturated hydrocarbons, aromatic structures and highly oxygenated compounds (HOCs). Lipid-like, aliphatic/peptide-like and CRAMs-like compounds were the most impacted since they were consumed to maintain the microbial metabolism. On the contrary, the relative percentages of CRAMs and carbohydrates increased after incubation.

Clouds constitute the uppermost layer of the biosphere. They host diverse communities whose functioning remains obscure, although biological activity potentially participates to atmospheric chemical and physical processes. In order to gain information on the metabolic functioning of microbial communities in clouds, we conducted coordinated metagenomics/metatranscriptomics profiling of cloud water microbial communities. Samples were collected from a high altitude atmospheric station in France and examined for biological content after untargeted amplification of nucleic acids. Living microorganisms, essentially bacteria, maintained transcriptional and translational activities and expressed many known complementary physiological responses intended to fight oxidants, osmotic variations and cold. These included activities of oxidant detoxification and regulation, synthesis of osmoprotectants/cryoprotectants, modifications of membranes, iron uptake. Consistently these energy-demanding processes were fueled by central metabolic routes involved in oxidative stress response and redox homeostasis management, such as pentose phosphate and glyoxylate pathways. Elevated binding and transmembrane ion transports demonstrated important interactions between cells and their cloud droplet chemical environments. In addition, polysaccharides, potentially beneficial for survival like exopolysaccharides, biosurfactants and adhesins, were synthesized. Our results support a biological influence on cloud physical and chemical processes, acting notably on the oxidant capacity, iron speciation and availability, amino-acids distribution and carbon and nitrogen fates.

Clouds are key components in Earth's functioning. In addition of acting as obstacles to light radiations and chemical reactors, they are possible atmospheric oases for airborne microorganisms, providing water, nutrients and paths to the ground. Microbial activity was previously detected in clouds, but the microbial community that is active in situ remains unknown. Here, microbial communities in cloud water collected at puy de Dôme Mountain's meteorological station (1465 m altitude, France) were fixed upon sampling and examined by high-throughput sequencing from DNA and RNA extracts, so as to identify active species among community members. Communities consisted of ~103-104 bacteria and archaea mL-1 and ~102-103 eukaryote cells mL-1. They appeared extremely rich, with more than 28 000 distinct species detected in bacteria and 2 600 in eukaryotes. Proteobacteria and Bacteroidetes largely dominated in bacteria, while eukaryotes were essentially distributed among Fungi, Stramenopiles and Alveolata. Within these complex communities, the active members of cloud microbiota were identified as Alpha- (Sphingomonadales, Rhodospirillales and Rhizobiales), Beta- (Burkholderiales) and Gamma-Proteobacteria (Pseudomonadales). These groups of bacteria usually classified as epiphytic are probably the best candidates for interfering with abiotic chemical processes in clouds, and the most prone to successful aerial dispersion.

Within cloud water, microorganisms are metabolically active and, thus, are expected to contribute to the atmospheric chemistry. This article investigates the interactions between microorganisms and the reactive oxygenated species that are present in cloud water because these chemical compounds drive the oxidant capacity of the cloud system. Real cloud water samples with contrasting features (marine, continental, and urban) were taken from the puy de Dôme mountain (France). The samples exhibited a high microbial biodiversity and complex chemical composition. The media were incubated in the dark and subjected to UV radiation in specifically designed photo-bioreactors. The concentrations of H(2)O(2), organic compounds, and the ATP/ADP ratio were monitored during the incubation period. The microorganisms remained metabolically active in the presence of ()OH radicals that were photo-produced from H(2)O(2). This oxidant and major carbon compounds (formaldehyde and carboxylic acids) were biodegraded by the endogenous microflora. This work suggests that microorganisms could play a double role in atmospheric chemistry; first, they could directly metabolize organic carbon species, and second, they could reduce the available source of radicals through their oxidative metabolism. Consequently, molecules such as H(2)O(2) would no longer be available for photochemical or other chemical reactions, which would decrease the cloud oxidant capacity.

Bacteria circulate in the atmosphere, through clouds and precipitation to surface ecosystems. Here, we conducted a coordinated study of bacteria assemblages in clouds and precipitation at two sites distant of ∼800 m in elevation in a rural vegetated area around puy de Dôme Mountain, France, and analysed them in regard to meteorological, chemical and air masses' history data. In both clouds and precipitation, bacteria generally associated with vegetation or soil dominated. Elevated ATP-to-cell ratio in clouds compared with precipitation suggested a higher proportion of viable cells and/or specific biological processes. The increase of bacterial cell concentration from clouds to precipitation indicated strong below-cloud scavenging. Using ions as tracers, we derive that 0.2 to 25.5% of the 1.1 × 107 to 6.6 × 108 bacteria cell/m2/h1 deposited with precipitation originated from the source clouds. Yet, the relative species richness decreased with the proportion of inputs from clouds, pointing them as sources of distant microbial diversity. Biodiversity profiles, thus, differed between clouds and precipitation in relation with distant/local influencing sources, and potentially with bacterial phenotypic traits. Notably Undibacterium , Bacillus and Staphylococcus were more represented in clouds, while epiphytic bacteria such as Massilia , Sphingomonas , Rhodococcus and Pseudomonas were enriched in precipitation. [ABSTRACT FROM AUTHOR]

Evaluates multiphase chemistry versus the overall tropospheric chemistry and its role in the earth's radiative budget. Effect of multiphase chemistry on cloud optical properties; Aspects of chemical reactivity within the cloud; Source of metals in the atmospheric aqueous phase.

Abstract: Despite the enormous volume they represent and the importance they have for Earth’s climate, clouds remain environments where the microbiological features are still poorly understood. Studies of the microbial content existing in the atmosphere have demonstrated extreme quantitative and qualitative variability, of which the drivers yet need to be determined. Between 2007 and 2010, we collected cloud water from the puy de Dôme summit in France (1465m a.s.l.) for chemical and microbiological analysis. These data were combined with cloud data collected between 2004 and 2005 following similar protocols. Overall, the cultivable community of chemotrophic aerobic microorganisms was dominated by pigmented colonies and accounted for <1% of the 3.3×103 to 2.5×105 total bacteria mL−1, but up to 41% of the 8.9×102 to 3.2×104 fungal cells mL−1. None of the concentrations of the chemical compounds measured was linked to the variations observed for the microbiological content, suggesting distinct sources and/or distinct modes of incorporation into cloud water. However, the overall dataset indicated that microorganisms in clouds were mostly originating from continental areas, especially from vegetation. We isolated and identified 185 heterotrophic bacteria and 150 yeasts from our samples (including -Alpha, -Beta and Gamma-Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria, and Basidiomycetous and Ascomycetous yeasts), the corresponding 16S and 26S rRNA gene sequences of which have been deposited in GenBank. A few genera largely dominated the pool of cultivable microorganisms in clouds, such as Pseudomonas and Sphingomonas for bacteria, which were detected in more than 40% of the clouds sampled, and Dioszegia and Udeniomyces for yeasts, detected in more than 60% of the samples. The recurring presence of some groups of microorganisms suggests that they have elaborated strategies of increased survival in the atmosphere and clouds. [Copyright &y& Elsevier]

Abstract: In the first part of the work, we investigated the reactivity toward photogenerated hydroxyl radicals ( OH) of seven monocarboxylic acids and six dicarboxylic acids found in natural cloud water. This leads to the proposition of a schematic degradation pathway linking glutaric acid (C5) to complete mineralization into CO2. We report a detailed mechanism on the succinic acid reactivity toward OH leading to the formation of malonic, glyoxylic and consequently oxalic acids and a comparison with reported pathways proposed by the CAPRAM (Chemical Aqueous Phase RAdical Mechanism) is discussed. We also investigated the photooxidation of formic acid under atmospherically relevant conditions leading to the possible formation of oxalic acid via radical mediated recombination. The second part focuses on the polychromatic irradiation (closed to solar irradiation) of a collected cloud aqueous phase showing that irradiation of cloud water leads to the formation of both formic and acetic acids. Carboxylic acid formation increases in the presence of photogenerated hydroxyl radicals from hydrogen peroxide, showing that photooxidation could play a key role in the formation of carboxylic acids under atmospherically relevant conditions. [Copyright &y& Elsevier]

VOC precursors play a key role in air quality and climate by contributing to ozone productionand by modifying the physicochemical properties of aerosols, one of the main agents of theEarth&#x2019;s radiative forcing. Among VOCs, oxygenated VOC (OVOC) and biogenic VOC(BVOC) are of particular interest due to their high reactivity. Meanwhile, the cloud systemrepresents a multiphase medium (gas, aerosol, water) for transformations of VOC andparticularly of OVOC, highly soluble. Indeed, cloud droplets, which are able to trap and dissolve many gaseous and particulatecompounds, represent a very reactive media in the atmosphere. Microphysical processescontrol formation, lifetime and dissipation of the clouds and consequently modify thedistribution of the chemical species between the different reservoirs (cloud water, rain,particle phase, gaseous phase, and solid ice phase). Meanwhile, photochemical processesinside the droplets are strongly amplified when compared with the interstitial air.However, speciation and concentrations of organic compounds between gaseousphase (interstitial air) and atmospheric liquid phase (cloud droplets) are still poorlydescribed. Our objectives are to collect air and cloud water simultaneously by using differentsamplers and to characterize the gas/liquid partitioning of target organic compounds (OVOC,BVOC) that are considered as efficient SOA precursors both in the aqueous phase andgaseous phase. Several cloud events were sampled at the puy de Dôme station (PUY) in thecentre of France (1465 m a.s.l.) belonging to the GAW/ACTRIS network. Air massesreaching the summit present contrasted origins (from the marine influence to theanthropogenic one). A new analytical approach has been optimized (i.e., linearity, repeatability, sensitivity andrelative humidity) to explore VOCs in both gas and liquid phases by taking into account realcloud conditions. First, a newly developed gas sampler (AEROVOCC) collectsgaseous VOCs/OVOCs (–C=O and –OH functional groups) simultaneously bydeploying three types of Tenax TA sorbent tubes pre-coated with different derivatisationreagents. Simultaneously, cloud sampling is performed with a cloud collector. Then,(O)VOC concentrations in the cloud water samples are evaluated by using directliquid derivatization and extraction by Stir Bar Sorptive Extraction (SBSE). Finally,collected both gas and aqueous samples are analysed by desorption (TD) coupledwith gas chromatography (GC) and mass spectrometry (MS) at the laboratory. Thewhole set-up has been deployed on the field to study the partitioning of VOCs; thisexperimental partitioning is evaluated towards the theoretical one described bythe Henry&#x2019;s Law constants. Our results show that even observed concentrations ofhydrophobic VOCs are significant in the cloud droplet and supersaturated by afactor of 10-10000. Larger and less soluble carbonyl compounds were found to besupersaturated by a factor of 100-1000 in other studies. This result suggests that thepool of reactive organic compounds in the cloud phase is largely underestimated. [ABSTRACT FROM AUTHOR]