Potential impact of microbial activity on the oxidant capacity and organic carbon budget in clouds

Abstract

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 photoproduced 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.biodegradation | cloud chemistry T he cloud system is an ideal medium for the development of complex multiphase chemistry, in which chemical species from the gas, solid, and aqueous phases are transformed. This process perturbs the homogeneous gas phase chemistry through the dissolution of various chemical compounds that undergo efficient photochemical processing. During a cloud's lifetime, cloud chemistry can lead to the formation of new, low volatile compounds, such as organic and inorganic acids, that modify the physical and chemical properties of aerosols after cloud evaporation and can also contribute to the formation of secondary aerosols (1, 2). The formation of clouds is, consequently, modified, and this process remains one of the major uncertainties in climate models that assess the earth's radiative balance (3).Within this framework, the presence of free radicals and oxidants in the cloud system leads to aqueous phase oxidations, transforming both inorganic and organic compounds. Cloud chemistry models predict that the • OH radicals represent the most important oxidant in the cloud aqueous phase (4). This oxidant can either be transferred from the gas phase or produced in situ in the aqueous phase through photochemical processes or related reactions with hydrogen peroxide and transition metal ions, such as iron (5). Multiple other oxidants that are produced in clouds can also oxidize chemicals, and these oxidation processes must be better understood because they impact atmospheric chemical cycles and radiation. Indeed, the resulting aerosols increase or decrease the scattering a...

Vertical distribution of airborne bacterial communities in an Asian-dust downwind area, Noto Peninsula

“…Viable bacteria have been identified in super cooled cloud droplets, and their ability to metabolize organic matters in the environment has been confirmed (Sattler et al, 2001;Vaïtilingom et al, 2013).…”

A better understanding of hydroxyl radical photochemical sources in cloud waters collected at the puy de Dôme station – experimental versus modelled formation rates

“…It has been previously demonstrated that filtration does not modify the soluble iron quantification in natural cloud water samples (Parazols et al, 2006;Vaitilingom et al, 2013). It is not possible to measure particulate iron because the ferrozine method cannot solubilize solid phase-iron (the contact time between acidic reagents and particulate iron is too short).…”

H<sub>2</sub>O<sub>2</sub> modulates the energetic metabolism of the cloud microbiome

“…Vaïtilingom et al (2013) have demonstrated that microorganisms present in real cloud water are able to efficiently degrade hydrogen peroxide. This suggests that cloud microorganisms found strategies to survive and resist stresses encountered in this medium, and in particular oxidative stress.…”

“…A few decades ago, living microorganisms were observed in cloud water (Sattler et al, 2001;Amato et al, 2005Amato et al, , 2007aWei et al, 2017). Particularly through measurements of adenosine triphosphate (ATP) and anabolic precursors or nutrient incorporation rates, it has been shown that cloud microorganisms are metabolically active and play an important role in cloud chemical reactivity (Sattler et al, 2001;Amato et al, 2007a;Hill et al, 2007;Vaïtilingom et al, 2012Vaïtilingom et al, , 2013. Several studies performed on simplified or real microcosms have demonstrated that cloud microorganisms are able to degrade carbon compounds (Ariya et al, 2002;Amato et al, 2005Amato et al, , 2007cHusarova et al, 2011;Vaïtilingom et al, 2010Vaïtilingom et al, , 2011Vaïtilingom et al, , 2013Matulovà et al, 2014); recent studies have also shown that this could be the case in the air (Krumins et al, 2014).…”

“…), incubated in a photo-bioreactor designed to mimic cloud conditions (Vaïtilingom et al, 2013). Thanks to ADP/ATP ratio measurements, reflecting the energetic metabolism of microorganisms, exposed or not to solar radiation, it has been shown that microorganisms were not impacted by artificial light and consequently by the generation of radicals from H 2 O 2 photo-reactivity.…”