GlpR Regulates Motility and Viscoelasticity Properties of Pseudomonas aeruginosa

Abstract

Despite the onset of highly effective modulator therapies people with Cystic Fibrosis continue to experience recurrent microbial lung infections. Many of these individuals will have at least one positive culture per year for Pseudomonas aeruginosa, a bacterium that readily adapts to chronic CF airway disease. Of these adaptations, the formation of a protective biofilm and changes in motility are hallmarks of established infections. We have shown previous evidence that glycerol metabolism and the P. aeruginosa glycerol regulon repressor, GlpR, is linked to enhanced biofilm production and reduced susceptibility to tobramycin. In the current study, we report that loss of GlpR contributes to higher viscosity and elasticity in synthetic cystic fibrosis sputum media. Further, we show that the loss of the glycerol repressor GlpR, or growth on glycerol, both resulting in derepression of the GlpR/glycerol regulon, cause decreased motility in both acute and chronic CF-adapted lab strains. RNA sequencing analysis indicated that loss of GlpR altered the expression of genes involved in motility, iron scavenging, transport, metabolism, and virulence. An in silico search of P. aeruginosas genome using GlpRs previously determined binding consensus site identified potential bindings sites in genes related to biofilm development, motility, antibiotic resistance, and metabolism, and these binding sites were confirmed using chromatin immunoprecipitation sequencing. Collectively, our results indicate that GlpR regulates P. aeruginosa phenotypes that facilitate persistence in the CF airway and we provide evidence that GlpR regulates genes outside of the canonical glp regulon. IMPORTANCEPseudomonas aeruginosa continues to persist in the airways of individuals with cystic fibrosis (CF), even with modulator therapy. The nutritional environment of the CF airway has been shown to trigger the microevolution of P. aeruginosa to assist this bacterium in adaptation and persistence. P. aeruginosa can liberate glycerol from lung surfactant to use as a nutritional source. Previous studies have shown that glycerol metabolic genes are constitutively expressed in P. aeruginosa isolates recovered from CF sputum, highlighting the importance of the glp (glycerol) regulon, which is regulated by the transcriptional repressor, GlpR. Since glycerol is a critical nutritional source for P. aeruginosa adaptation, it is essential to understand the regulatory network controlled by GlpR.