Activation of the <i>Pseudomonas aeruginosa</i> glycerol regulon reduces antibiotic susceptibility and modulates virulence phenotypes

Chronic infections with <i>Pseudomonas aeruginosa</i> are a major contributor of lung decline in persons with cystic fibrosis (pwCF). <i>P. aeruginosa</i> establishes life-long infections in the CF airway by utilizing various adaptation strategies to persist, including altering the expression of metabolic genes to acquire nutrients that are abundant in the CF airway. Glycerol, which is readily available in the airway, is imported and metabolized by genes in the <i>glp</i> regulon, which is under the control of the GlpR repressor. Previously, it has been shown that the loss of GlpR results in increased biofilm development in a CF-adapted isolate of <i>P. aeruginosa</i> compared to a wound isolate. Based on the increased biofilm phenotype previously observed and because biofilms are associated with reduced antibiotic susceptibility, we questioned whether GlpR plays a role in mediating antibiotic susceptibility of <i>P. aeruginosa</i>. In this report, we show that loss of GlpR reduces tobramycin susceptibility of a CF-adapted isolate in synthetic sputum and in airway epithelial cell and <i>Drosophila melanogaster</i> colonization models. Furthermore, transcriptomics analysis revealed that CF-adapted mutants of <i>glpR</i> overexpress genes involved in multidrug resistance and chronic infection phenotypes such as alginate. In summary, our study illustrates that the activation of the glycerol (<i>glp</i>) regulon may promote <i>P. aeruginosa</i> persistence in the CF airway.