Atmos. Chem. Phys. Discuss., 7, 5253-5276, 2007
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
A fate for organic acids, formaldehyde and methanol in cloud water: their biotransformation by micro-organisms
P. Amato1,2,*, F. Demeer1, A. Melaouhi1, S. Fontanella1, A.-S. Martin-Biesse1, M. Sancelme1, P. Laj2, and A.-M. Delort1,*
1Laboratoire de Synthèse et Etudes de Systèmes à Intérêt Biologique, UMR 6504 CNRS-Université Blaise Pascal, Aubière, France
2Laboratoire de Météorologie Physique, UMR 6016 CNRS-Université Blaise Pascal Aubière, France
*now at: Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, USA

Abstract. The interactions between microbial and chemical contents of cloud water were investigated. First, we observe that the bulk cloud water solution provides a substantial environment where bacteria can develop significantly. Then, a total number of 60 microbial strains originating from seven distinct samples of cloud water and affiliated to various taxonomic groups were looked for their ability to degrade some of the main atmospheric carboxylic compounds: formate, acetate, lactate, succinate, formaldehyde and methanol. Biodegradation tests show that all these compounds can be transformed when used as single carbonaceous substrates, with activities depending on both the strain and the compound. The highest capacities of biodegradation are observed towards formaldehyde, formate and acetate, which are also the more concentrated compounds typically measured in cloud water. Hence, analyses by 1H NMR permitted to establish for instance that compounds like pyruvate or fumarate can be produced and released in the media in relation to the transformation of lactate or succinate. In addition, utilization of 13C labelled formaldehyde showed that it can be transformed through many metabolic pathways, similar to those induced by photochemistry and leading to the production of formate and/or methanol. These results suggest that microorganisms of cloud water can have various behaviours towards the chemical compounds present in the atmosphere: they can represent either a sink or source for organic carbon, and may have to be considered as actors of cloud chemistry.

Citation: Amato, P., Demeer, F., Melaouhi, A., Fontanella, S., Martin-Biesse, A.-S., Sancelme, M., Laj, P., and Delort, A.-M.: A fate for organic acids, formaldehyde and methanol in cloud water: their biotransformation by micro-organisms, Atmos. Chem. Phys. Discuss., 7, 5253-5276, doi:10.5194/acpd-7-5253-2007, 2007.
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