Pseudomonas aeruginosa AmpR Is a Global Transcriptional Factor That Regulates Expression of AmpC and PoxB β-Lactamases, Proteases, Quorum Sensing, and Other Virulence Factors

Abstract

ABSTRACT In members of the family Enterobacteriaceae , ampC , which encodes a β-lactamase, is regulated by an upstream, divergently transcribed gene, ampR . However, in Pseudomonas aeruginosa , the regulation of ampC is not understood. In this study, we compared the characteristics of a P. aeruginosa ampR mutant, PAO ampR , with that of an isogenic ampR + parent. The ampR mutation greatly altered AmpC production. In the absence of antibiotic, PAO ampR expressed increased basal β-lactamase levels. However, this increase was not followed by a concomitant increase in the P ampC promoter activity. The discrepancy in protein and transcription analyses led us to discover the presence of another chromosomal AmpR-regulated β-lactamase, PoxB. We found that the expression of P. aeruginosa ampR greatly altered the β-lactamase production from ampC and poxB in Escherichia coli : it up-regulated AmpC but down-regulated PoxB activities. In addition, the constitutive P ampR promoter activity in PAO ampR indicated that AmpR did not autoregulate in the absence or presence of inducers. We further demonstrated that AmpR is a global regulator because the strain carrying the ampR mutation produced higher levels of pyocyanin and LasA protease and lower levels of LasB elastase than the wild-type strain. The increase in LasA levels was positively correlated with the P lasA , P lasI , and P lasR expression. The reduction in the LasB activity was positively correlated with the P rhlR expression. Thus, AmpR plays a dual role, positively regulating the ampC , lasB , and rhlR expression levels and negatively regulating the poxB , lasA , lasI , and lasR expression levels.