Investigator: Anne Reid, Salve Regina University
Theme: Environmental Health Sciences
Title: Impact of flagellin methylation on plant immune responses against human pathogens
Award: SURF PUI Training Award (2022-2024)
Abstract: Over 1 million cases of salmonellosis occur annually in the US, with outbreaks increasingly linked to fresh fruits and vegetables. Bacterial flagella mediate swimming motility as well as adherence to biotic and abiotic surfaces and are recognized by plant and animal immune systems. Many bacteria vary their flagellin proteins via altered sequences and post-translational modification. The role of flagellin methylation in the environmental fitness of the human pathogen, Salmonella enterica, is currently unknown. This research project seeks to determine whether flagellin methylation influences interactions between human pathogens and plants. Changes in methylation levels are expected to affect flagellin recognition and the strength of the immune response mounted by plants in response to contact with these human pathogens. Improved knowledge of mechanisms that favor S. enterica’s colonization of plants could be leveraged to decrease the burden of foodborne diseases in the US.
Specific Aim 1: Influence of methylation levels on Salmonella-plant interactions. Deletion mutants of the flagellin methylase, fliB, will be used to study the effect of reduced methylation on plant-bacterium interactions. Conversely, the fliB gene will be overexpressed in S. enterica strains to study the impact of increased flagellin methylation on these interactions. The model plant system Arabidopsis thaliana will be used for these studies, and immune activation will be assessed by microscopic examination of stomatal opening and callose deposition, reactive oxygen species production, and expression levels of plant defense genes by qPCR.
Specific Aim 2: Induction of flagellin methylation in Escherichia coli. E. coli does not modify its flagellin proteins and triggers a stronger plant immune response than S. enterica. The cloned flagellin methylase of S. enterica will be expressed in E. coli and flagellin methylation sites and levels will be mapped by Mass Spectrometry. The ability of wild-type and fliB-expressing E. coli to activate the A. thaliana immune response will be assessed as described in aim 1.
Relevance: The contamination of fresh foods by S. enterica and other human pathogens is an important environmental health issue, as this can lead to costly and devastating multistate outbreaks. A better understanding of the molecular mechanisms used by human pathogens to interact with plants could inform the development of practices to interfere with these interactions and decrease the burden of foodborne disease in the United States.