Potential role of the cloud microbiote in atmospheric processes
Imparte: Anne-Marie Delort, Institute of Chemistry of Clermont-Ferrand, France
lthough microorganisms were discovered by Pasteur in the air, the investigation of their activity in the atmospheric compartment is rather recent. Our team works mainly on microorganisms present in clouds1. Cloud samples are collected at the puy de Dôme observatory which is labelled at the international level as a GAW (Global Atmosphere Watch) station.
Our objective is to study the potential role of microorganisms in the chemistry and the microphysics of clouds.
First we have shown that microorganisms are metabolically active in clouds and can thus potentially modify the chemical composition of clouds and be an alternative route to radical chemistry. We have mainly studied the biotransformation of simple carbon compounds (acetate, succinate, formate, methanol, formaldehyde), or of oxidants (H2O2). Biodegradation rates are within the same range of order than photo-transformation rates; the cloud microbiote could play thus an active role in atmospheric chemistry2.
Second, concerning cloud microphysics, we have looked at the potential role of microorganisms in the formation of cloud droplets. In addition to their CCN properties (Cloud Condensation Nuclei), some microorganisms can produce biosurfactants that can modify the surface tension of the droplets and thus their size. We have screened a large number of cloud microorganisms for their ability to produce such biosurfactants by using the pending drop method3.
In addition, some bacteria from the phyllosphere, particularly belonging to the Pseudomonas genus, have surface proteins that induce the formation of ice at rather high temperature (from -2 to -8°C) and could be thus very efficient IN (Ice Nuclei) in the atmosphere. Indeed pure water freezes at -39°C and non-biological IN are efficient at -15°C. We have shown that IN active microorganisms were present in cloud waters and could thus induce precipitations4,5.
Finally we try to understand how microorganisms adapt their metabolism facing atmospheric stresses (cold, oxidants, light, freeze-thaw cycle, osmotic shocks etc…). We have studied in great details the modulation of the cloud microbiome metabolism by H2O2, the major oxidant of cloud waters6.
1P. AMATO, M. JOLY, L. BESAURY, A. OUDART, N TAIB, A. MONE, L. DEGUILLAUME, A.M. DELORT, D. DEBROAS. (2017). Active microorganisms thrive among extremely diverse communities in cloud water. PLoS ONE. 2017,12(8):e0182869.https://doi.org/10.1371/journal.pone.0182869.me.
2M. VAÏTILINGOM, L. DEGUILLAUME, V. VINATIER, M. SANCELME, P. AMATO, N. CHAUMERLIAC, A-M DELORT. Potential impact of microbial activity on the oxidant capacity and organic carbon budget in clouds. PNAS USA, 2013, 110, 559-564.
3P. RENARD, I. CANET, M. SANCELME, N. WIRGOT, L. DEGUILLAUM , A.-M. DELORT. Screening of cloud microorganisms isolated at the puy de Dôme (France) station for the production of biosurfactants, Atmos. Chem. Phys. 2016, 16, 12347-12358.
4M. JOLY, P. AMATO, L. DEGUILLAUME, M. MONIE R, C. HOOSE, A.-M. DELORT. Quantification of ice nuclei active at near 0°C temperatures in low-altitude clouds at the Puy de Dôme atmospheric station. Atmos. Chem. Phys., 2014, 14, 8185-8195.
5P. AMATO, M. JOLY, C. SCHAUPP, E. ATTARD, O. MOEHLER, C. E ; MORRIS, Y. BRUNET, A.-M. DELORT. Survival and ice nucleation activity of bacteria as aerosol in a cloud simulation chamber. Atmos. Chem. Phys, 2015, 15, 6455-6465.
6N. WIRGOT, V. VINATIER, L. DEGUILLAUME, M. SANCELME, A.-M. DELORT.. H2O2 modulates the metabolic activity of the cloud microbiome. Atmos. Chem. Phys. 2017, 17, 14841-14851, https://doi.org/10.5194/acp-17-14841-2017.