Metabolomic study of the response to cold shock in a strain of Pseudomonas syringae isolated from cloud water

Introduction Active microorganisms have been recently discovered in clouds, thus demonstrating the capacity of microorganisms to exist in harsh environments, including exposure to UV and oxidants, osmotic and cold shocks, etc. It is important to understand how microorganisms respond to and survive such stresses at the metabolic level. Objectives The objective of this work is to assess metabolome modulation in a strain of Pseudomonas syringae isolated from cloud water and facing temperature downshift from 17 to 5 degrees C by identifying key molecules and pathways of the response/adaptation to cold shock. Methods Bacterial extracts from suspensions of cells grown at 17 degrees C and further incubated in microcosms at 5 and 17 degrees C to mimic cloud conditions were analysed by combining LC-MS and NMR; the results were evaluated in comparison to similar suspensions kept at constant temperature. The differences in the metabolome profiles were deciphered using multivariate statistics (PLS-DA). Results Key cold shock biomarkers were observed, including cryoprotectants (trehalose, glucose, glycerol, carnitine, glutamate), antioxidants (glutathione and carnitine) and their precursors, alkaloids (bellendine and slaframine) and metabolites involved in energy metabolism (ATP, carbohydrates). Furthermore, new short peptides (nine dipeptides and a tetrapeptide) were found that have no known function. Conclusions This study shows that in response to cold temperatures, Pseudomonas syringae PDD-32b-74 demonstrates numerous metabolism modifications to counteract the impacts of low temperatures.