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Poster

Session: Session 1 Presenting Authors at Posters (Evens)

P-196 - Oxidative stress tolerance in the plant pathogen Pseudomonas syringae

Tuesday, July 15, 2025
09:55 - 11:30  
Location: Confex Hall 3
Microbial infection strategies (pathogens & non-pathogens)
During host colonisation the plant-associated bacterium Pseudomonas syringae encounters

reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), released by the host, as well

as endogenous ROS generated in response to environmental stressors. P. syringae must suppress

the release of or tolerate ROS to prevent lethal oxidative stress. Different P. syringae strains from

a number of phylogroups exhibit varying abilities to tolerate ROS, but the causes are not fully

understood. Upon exposure to H2O2, the transcriptional regulator OyxR plays a vital role by

regulating genes involved in the response to H2O2. By predicting the OxyR regulon for strains with

varying H2O2 tolerances and correlating this with RNA-seq data containing gene expression

changes in two model strains under H2O2 treatment, we have identified candidate genes that may

contribute to the differences in ROS tolerance. One candidate is an operon encoding an alternative

methionine biosynthesis pathway that is only present in higher tolerance strains potentially

providing an alternative way to synthesise methionine, especially under oxidative stress. In vitro

experiments with a knockout mutant of the operon demonstrates a two-fold reduction in H2O2

tolerance. Further characterisation of these candidates will help us to further understand how
the synthesis and metabolism of key metabolites contributes to bacterial stress tolerance and

infection outcomes and inform the development of targeted antimicrobials.