AEM Accepts, published online ahead of print on 23 October 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01127-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Contribution of microbial activity to carbon chemistry in clouds

Mickaël Vaitilingom, Pierre Amato, Martine Sancelme, Paolo Laj, Maud Leriche, and Anne-Marie Delort^*

Clermont Université, UBP, Laboratoire SEESIB, BP 10448, F-63000 CLERMONT-FERRAND; CNRS, UMR 6504, F-63177 Aubière; Clermont Université, UBP, LaMP, BP 10448, F-63000 CLERMONT-FERRAND; Laboratoire d'Aérologie, Université Paul Sabatier, Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France; CNRS, UMR 5560, F-31400 Toulouse

^* To whom correspondence should be addressed. Email: A-Marie.DELORT{at}univ-bpclermont.fr.

The biodegradation of the most abundant atmospheric organic C1-C4 compounds (formate, acetate, lactate, succinate) by five selected representative microbial strains (3 Pseudomonas, 1 Sphingomonas and 1 yeast) isolated from cloud water at the puy de Dôme have been studied. Experiments were first conducted under model conditions and consisted of a pure strain incubated in the presence of a single organic compound. Kinetics showed the ability of the isolates to degrade atmospheric compounds at temperatures representative of low altitude clouds (5°C and 17°C). Then, to provide data that can be extrapolated to real situations, microcosm experiments were developed. A solution that chemically mimicked that of cloud water was used as an incubation medium for microbial strains. Under these conditions, we determined that microbial activity would significantly contribute to the degradation of formate, acetate and succinate in cloud water at 5°C and 17°C, with lifetimes of 0.4 to 69.1 days. Compared with the reactivity involving free radicals, our results suggest that biological activity drives the oxidation of carbonaceous compounds during the night (90 to 99 %), while its contribution accounts for 2 to 37% of the reactivity during the day, competing with photochemistry.