Metabolic modulations of Pseudomonas graminis in response to H(2)O(2) in cloud water

In cloud water, microorganisms are exposed to very strong stresses especially related to the presence of reactive oxygen species including H(2)O(2) and radicals, which are the driving force of cloud chemistry. In order to understand how the bacterium Pseudomonas graminis isolated from cloud water respond to this oxidative stress, it was incubated in microcosms containing a synthetic solution of cloud water in the presence or in the absence of H(2)O(2). P. graminis metabolome was examined by LC-MS and NMR after 50 min and after 24 hours of incubation. After 50 min, the cells were metabolizing H(2)O(2) while this compound was still present in the medium, and it was completely biodegraded after 24 hours. Cells exposed to H(2)O(2) had a distinct metabolome as compared to unexposed cells, revealing modulations of certain metabolic pathways in response to oxidative stress. These data indicated that the regulations observed mainly involved carbohydrate, glutathione, energy, lipid, peptides and amino-acids metabolisms. When cells had detoxified H(2)O(2) from the medium, their metabolome was not distinguishable anymore from unexposed cells, highlighting the capacity of resilience of this bacterium. This work illustrates the interactions existing between the cloud microbial metabolome and cloud chemistry.