METACLOUD

Clouds play a major role in atmospheric chemical reactivity. They are complex multiphase environments of gas, liquid and solid particles. In the last decade, considerable progress has been made in understanding the reactivity of these multiphase systems, notably with the discovery of active microbial communities potentially involved in organic matter transformations in clouds. Nonetheless, nighttime atmospheric chemistry remains poorly understood, especially since biological activity may drive the chemical transformations at night. The role of microbial activity needs to be considered in numerical models of cloud chemistry. To date, no numerical models have taken into account these biological processes. The objective of METACLOUD is to improve the fundamental understanding of the cloud system, including its chemistry and biodiversity. More specifically, we want to assess the potential role of microbial metabolism in C1 chemistry in clouds, particularly at night. This will be achieved by: i) obtaining novel and detailed data on cloud microbiome metabolic networks and their modulations in contrasting atmospheric scenarios, in particular with detailed "meta-fluxome maps" to reveal the dynamics of the system; ii) integrating this new knowledge, in particular biodegradation rates of C1 compounds, into new explicit numerical models of cloud multiphase chemistry. This project focuses on C1 compounds, the major end products of radical chemistry, and in particularly, on formaldehyde. Formaldehyde is found at highly concentrations in clouds (microM) and is at the intersection of several metabolic pathways in methylotrophic microorganisms. Large cloud water samples will be collected from the puy de Dôme observatory (France), an international reference site for atmospheric research, using cloud droplet collectors constructed in 2018. The chemical content and microbial biodiversity will be characterized. After tangential filtration concentration, the endogenous microorganisms will be incubated in microcosms. These microcosms were designed to mimic contrasted "summer day" (light, H2O2, 17°C) or "winter night" (dark, no H2O2, 5°C) scenarios, representing reference scenarios of atmospheric chemistry. The behaviour of the microbial communities will be assessed by transcriptomics and metabolomics under these two atmospheric scenarios. The integration of these "omics" data will give a completely new "metabolic network map" that will be exploited to validate the Meta-fluxome map of C1 compounds determined using 13C-formaldehyde. Metabolic fluxes will be measured from 13C-labelled compounds and the transformation rates implemented, along with the corresponding pathways, in a newly developed cloud chemistry numerical model. This project is ambitious and innovative both for its integrative, multidisciplinary concept ("biogeochemistry" of clouds, integration of biological data in atmospheric chemistry models) and the proposed methodologies (meta-fluxomics performed on a whole ecosystem is particularly new). The originality of the project relies on collaboration between LaMP and ICCF one of the few groups worldwide working on cloud microorganisms and their implication in atmospheric chemistry. It also benefits from the GMGM team with recognized expertise of microbial C1 metabolism and from the LISBP team’s unique expertise in developing fluxomics tools. The interdisciplinary nature of the project, linking cloud chemistry, modelling, and the study of the microbial behavior by "omics" approaches, is also, to the best of our knowledge, absolutely unique worldwide. Results will be disseminated in high impact factor reviews and journals, communications in major international conferences, an organized international workshop, communications to the general public, active participation in education (summer schools, "Les cours d’eau H2O" for scholars), and production of a dedicated open source software.