Pseudomonas aeruginosa biofilm antibiotic resistance gene ndvB 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 Pseudomonas aeruginosa, 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 ndvB, 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 ndvB. We found that in addition to its expression in biofilms, ndvB was upregulated in planktonic cells as they enter stationary phase. The transcription of ndvB 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 ndvB promoter abolished the activity of the promoter in stationary-phase cells. Overall, we have expanded our understanding of the temporal expression of ndvB in P. aeruginosa and have uncovered a regulatory basis for its growth phase-dependent expression.