His research focuses on multiphase chemistry inside clouds by a modeling approach. He participates in the Exchange program within the European Science Foundation activity entitled "Interdisciplinary Tropospheric Research: from the laboratory to global change". From July 2005, he will carry out postdoctoral research on mesoscale chemistry modeling at the Laboratoire Inter-Universitaire des Systèmes Atmosphérique in Paris. Maud Leriche was born in Le Havre, France, in 1974. She received her B.Sc. in physics from Pierre et Marie Curie University (Paris, France) in 1995 and, then, her M.Sc. in atmospheric physics from the Blaise Pascal University (Clermont-Ferrand, France) in 1997. She obtained her Ph.D. in atmospheric physics and chemistry from Blaise Pascal University in 2000 with Dr. Nadine Chaumerliac, studying multiphase chemistry inside clouds. After a temporary position as assistant professor at Blaise Pascal University and a visiting fellowship from NATO at Harvard University with Professor Daniel Jacob, she joined the Centre National de la Recherche Scientifique in 2002, where she is presently a researcher at the Laboratoire de Météorologie Physique at Clermont-Ferrand. Her research interests are mainly in the areas of atmospheric cloud chemistry including the cloud processing of aerosols and the coupling between microphysical and chemical processes in clouds. She is involved in the international AMMA program looking at the redistribution of soluble chemical species by convective clouds. Karine V. Desboeufs received her M.Sc. in atmospheric chemistry in 1997 and her Ph.D. in 2001 from the Paris 7 University with Professor Jean-Louis Colin. Her graduate research focused on the dissolution processes of aerosol particles in cloud droplets and, more particularly, on the release of dissolved trace metals from dust particles. After her Ph.D., she worked as a CNES postdoctoral researcher at the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), where she performed atmospheric dust transport modeling to study interactions of dust particles with clouds. Currently, she is an assistant professor in chemistry at the Paris 7 University, and she develops her research in the LISA (Laboratoire Interuniversitaire des Systèmes Atmosphériques). Her research interests are iron biogeochemistry and its atmospheric cycling. Gilles Mailhot obtained his Ph.D. in physical chemistry in 1991 from the University Blaise Pascal at Clermont-Ferrand. He studied polymerization photoindiced by charge transfer in a coordination complex. After a postdoctoral fellowship under the supervision of Pr. Gabor Somorjai at the University of California in Berkeley, in 1995 he joined the Centre National de Recherche Scientifique, where he is presently a researcher at the Laboratoire de Photochimie Moléculaire et Macromoléculaire (Clermont-Ferrand, France). His research interests are principally in the areas of photochemistry. He especially focuses on pollutant decomposition in aquatic environments (continental waters, atmospheric liquid phases...

This work constitutes the first large report on aerobic cultivable microorganisms present in cloud water. Seven cloud-event samples were collected at the Puy de Dôme summit, and cultivation was performed leading to the isolation of 71 bacterial, 42 fungal and 15 yeast strains. Most of the fungi isolated were of Cladosporium or Trametes affiliation, and yeasts were of Cryptococcus affiliation. Bacteria, identified on the basis of their 16S rRNA gene sequence, were found to belong to Actinobacteria, Firmicutes, Proteobacteria (Alpha, Beta and Gamma subclasses) and Bacteroidetes phyla, and mainly to the genera Pseudomonas, Sphingomonas, Staphylococcus, Streptomyces, and Arthrobacter. These strains appear to be closely related to some bacteria described from cold environments, water (sea and freshwater), soil or vegetation. Comparison of the distribution of Gram-negative vs. Gram-positive bacteria shows that the number of Gram-negative bacteria is greater in summer than in winter. Finally, a very important result of this study concerns the ability of half of the tested strains to grow at low temperatures (5 degrees C): most of these are Gram-negative bacteria, and a few are even shown to be psychrophiles. On the whole, these results give a good picture of the microbial content of cloud water in terms of classification, and suggest that a large proportion of bacteria present in clouds have the capacity to be metabolically active there. This is of special interest with respect to the potential role of these microorganisms in atmospheric chemistry.