ThePseudomonas aeruginosaefflux pump MexGHI-OpmD transports a natural phenazine that controls gene expression and biofilm development

Abstract

Redox-cycling compounds, including endogenously produced phenazine antibiotics, induce expression of the efflux pump MexGHI-OpmD in the opportunistic pathogenPseudomonas aeruginosa. Previous studies ofP. aeruginosavirulence, physiology, and biofilm development have focused on the blue phenazine pyocyanin and the yellow phenazine-1-carboxylic acid (PCA). InP. aeruginosaphenazine biosynthesis, conversion of PCA to pyocyanin is presumed to proceed through the intermediate 5-methylphenazine-1-carboxylate (5-Me-PCA), a reactive compound that has eluded detection in most laboratory samples. Here, we apply electrochemical methods to directly detect 5-Me-PCA and find that it is transported by MexGHI-OpmD inP. aeruginosastrain PA14 planktonic and biofilm cells. We also show that 5-Me-PCA is sufficient to fully induce MexGHI-OpmD expression and that it is required for wild-type colony biofilm morphogenesis. These physiological effects are consistent with the high redox potential of 5-Me-PCA, which distinguishes it from other well-studiedP. aeruginosaphenazines. Our observations highlight the importance of this compound, which was previously overlooked due to the challenges associated with its detection, in the context ofP. aeruginosagene expression and multicellular behavior. This study constitutes a unique demonstration of efflux-based self-resistance, controlled by a simple circuit, in a Gram-negative pathogen.