Pseudomonas aeruginosa Biofilm Antibiotic Resistance Gene<i>ndvB</i>Expression Requires the RpoS Stationary-Phase Sigma Factor

Abstract

Chronic, biofilm-based bacterial infections are exceptionally difficult to eradicate due to the high degree of antibiotic recalcitrance exhibited by cells in biofilm communities. In the opportunistic pathogen <i>Pseudomonas aeruginosa</i>, biofilm recalcitrance is multifactorial and arises in part from the preferential expression of resistance genes in biofilms compared to exponential-phase planktonic cells. One such mechanism involves <i>ndvB</i>, which we have previously shown to be expressed specifically in biofilms. In this study, we investigated the regulatory basis of this lifestyle-specific expression by developing an unstable green fluorescent protein (GFP) transcriptional reporter to observe the expression pattern of <i>ndvB</i> We found that in addition to its expression in biofilms, <i>ndvB</i> was upregulated in planktonic cells as they enter stationary phase. The transcription of <i>ndvB</i> in both growth phases was shown to be dependent on the stationary-phase sigma factor RpoS, and mutation of a putative RpoS binding site in the <i>ndvB</i> promoter abolished the activity of the promoter in stationary-phase cells. Overall, we have expanded our understanding of the temporal expression of <i>ndvB</i> in <i>P. aeruginosa</i> and have uncovered a regulatory basis for its growth phase-dependent expression.<b>IMPORTANCE</b> Bacterial biofilms are more resistant to antibiotics than free-living planktonic cells, and understanding the mechanistic basis of this resistance can inform treatments of biofilm-based infections. In addition to chemical and structural barriers that can inhibit antibiotic entry, the upregulation of specific genes in biofilms contributes to the resistance. We investigated this biofilm-specific gene induction by examining expression patterns of <i>ndvB</i>, a gene involved in biofilm resistance of the opportunistic pathogen <i>Pseudomonas aeruginosa</i> We characterized <i>ndvB</i> expression in planktonic and biofilm growth conditions with an unstable green fluorescent protein (GFP) reporter and found that the expression of <i>ndvB</i> in biofilms is dependent on the stationary-phase sigma factor RpoS. Overall, our results support the physiological similarity between biofilms and stationary-phase cells and suggest that the induction of some stationary-phase genes in biofilms may contribute to their increased antibiotic resistance.