RUI: Acid Signals and Bacterial Drug Efflux Systems

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Plants produce aromatic acids related to aspirin that may limit or reverse bacterial drug resistance within the soil environment and gut microbiome. Exposure to salicylic acid selects for Escherichia coli strains that have lost multidrug resistance. The mechanism of the increased fitness cost is unclear, but may involve depletion of the bacterial cell's proton motive force, the energy source that powers drug efflux pumps. In this project, undergraduate researchers will dissect the mechanism of how organic acids reverse multidrug resistance. The "First-years First" program will recruit eight incoming undergraduate students annually (24 over three years) to conduct research, with supervision by the principal investigator and a team of advanced undergraduates. The recruitment program is designed to attract students from economically limited backgrounds and encourage them to pursue research careers in STEM.Competition assays by flow cytometry will reveal which drug-efflux genes of E. coli incur fitness cost in the presence of salicylate or jasmonate. The role of proton motive force will be tested by using drug pump blockers, which may decrease the fitness cost of the proton-driven pumps. The role of specific acid anions will be tested by comparing the effects of salicylate and jasmonate with that of their methyl esters. The hypothesis of drug resistance reversal will be extended beyond E. coli by salicylate-dependent experimental evolution of bacterial species relevant to plant, soil and human microbiomes, including the plant commensal Pseudomonas fluorescens, the soil bacterium Bacillus subtilis, and the soil and gut fermenter Enterococcus faecalis. FACS sorting of ethidium-labeled cells will identify mutants that lose multidrug pumps. Genomes and transcriptomes of salicylate-evolved clones will reveal the rewiring of regulatory pathways unique to each species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.