- 1Aarhus University, Denmark (temkiv@bio.au.dk)
- 2University of Vienna, Austria
- 3University of the Faroe Islands, Faroe Islands
Pseudomonas syringae is a common plant pathogen, posing significant threats to the global crop production. By producing ice-nucleating proteins (INpro), encoded by the inaZ gene, cells can inflict frost injuries to plants, gaining access to nutrient-rich plant tissue. Furthermore, P. syringae can impact cloud formation and interfere with atmospheric chemistry through their metabolic and ice-nucleation activity. Both metabolic activity and inaZ gene expression under atmospheric conditions remain poorly understood, limiting our ability to accurately predict the atmospheric impact and dispersal success of P. syringae.
Our fist aim was to investigate the metabolic activity of P. syringae at simulated atmospheric conditions. We exposed single cells placed on polycarbonate filters to RH 94-100% in presence of D2O. We used the incorporation of deuterium as an activity marker detected via nanoscale secondary ion mass spectrometry (NanoSIMS). Cells exhibited metabolic activity when liquid water was available (RH 100%) without the addition of carbon sources, suggesting that P. syringae can maintain activity based on storage compounds. While we observed a significant decrease in deuterium incoorporation when water was supplied through the vapor phase (<100% RH), likely due to reduced viability, a fraction of cells remained metabolically active at 97% and 94% RH. Interestingly, we observed deuterium incorporation in non-viable cells, likely because of residual enzymatic activity. Such residual enzymatic activity in dead airborne cells may have unknown impacts on atmospheric chemistry, which remain to be determined. Altogether, the results suggest that metabolic activity is possible both in cloud droplets and in dry atmosphere based on storage compounds available in cells, which could support cells in actively modifying their surface properties, by e.g. synthesizing novel INpro while airborne.
Our second aim was to investigate the effect of aerosolization on the inaZ gene expression in P. syringae. Using bubble-bursting aerosolization combined with immunofluorescence staining we found a significantly larger proportion of INpro-bearing cells in the aerosolized fraction (33.2%) compared to pre-aerosolization (10.7%). Using microbial adhesion to hydrocarbon test in combination with a droplet-freezing assay to quantify INpro-bearing cells, we found that cell surface hydrophobicity did not vary between INpro-bearing and other cells, suggesting that our observation was not linked to preferential aerosolization of INpro-bearing cells. Finally, we assessed the relation between cell viability and the number of INpro-bearing cells, to decipher whether INpro synthesis is triggered in aerosolized cells. Here, cells were aerosolized using a Sparging Liquid Aerosol Generator into a flow tube at varying RH and were recollected using different methods which both affected cell viability. Viability was determined by live/dead staining and flow cytometry. We found that the increase in INpro-bearing cell fraction after aerosolization, as determined via the droplet-freezing assay, correlated with the fraction of viable cells, suggesting that a stress response triggered inaZ gene expression leading to the synthesis of novel INpro.
Overall, we demonstrated that metabolic activity and inaZ gene expression is feasible in airborne P. syringae and leads to a significant increase in INpro-bearing cells. These processes may have profound impacts on cloud formation, atmospheric chemistry, and the dispersal success of P. syringae.
How to cite: Šantl-Temkiv, T., Wieber, C., Sánchez, M. P., Legin, A., Schintlmeister, A., Imminger, S., Christiansen, S., Ling, M., Isaksen, A. K., Bilde, M., Boesen, T., Woebken, D., Rosati, B., and Finster, K.: Metabolic activity and inaZ gene expression during atmospheric dispersal of plant pathogen Pseudomonas syringae , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19389, https://doi.org/10.5194/egusphere-egu25-19389, 2025.