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

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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, PAOampR, with that of an isogenic ampR+ parent. The ampR mutation greatly altered AmpC production. In the absence of antibiotic, PAOampR expressed increased basal β-lactamase levels. However, this increase was not followed by a concomitant increase in the PampC 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 PampR promoter activity in PAOampR 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 PlasA, PlasI, and PlasR expression. The reduction in the LasB activity was positively correlated with the PrhlR 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.

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