The Pseudomonas aeruginosa Two-Component Regulator AlgR Directly Activates <i>rsmA</i> Expression in a Phosphorylation-Independent Manner

Abstract

<i>Pseudomonas aeruginosa</i> is an important pathogen of the immunocompromised, causing both acute and chronic infections. In cystic fibrosis (CF) patients, <i>P. aeruginosa</i> causes chronic disease. The impressive sensory network of <i>P. aeruginosa</i> allows the bacterium to sense and respond to a variety of stimuli found in diverse environments. Transcriptional regulators, including alternative sigma factors and response regulators, integrate signals changing gene expression, allowing <i>P. aeruginosa</i> to cause infection. The two-component transcriptional regulator AlgR is important in <i>P. aeruginosa</i> pathogenesis in both acute and chronic infections. In chronic infections, AlgR and the alternative sigma factor AlgU activate the genes responsible for alginate production. Previous work demonstrated that AlgU controls <i>rsmA</i> expression. RsmA is a posttranscriptional regulator that is antagonized by two small RNAs, RsmY and RsmZ. In this work, we demonstrate that AlgR directly activates <i>rsmA</i> expression from the same promoter as AlgU. In addition, phosphorylation was not necessary for AlgR activation of <i>rsmA</i> using <i>algR</i> and <i>algZ</i> mutant strains. AlgU and AlgR appear to affect the antagonizing small RNAs <i>rsmY</i> and <i>rsmZ</i> indirectly. RsmA was active in a <i>mucA22</i> mutant strain using leader fusions of two RsmA targets, <i>tssA1</i> and <i>hcnA</i> AlgU and AlgR were necessary for posttranscriptional regulation of <i>tssA1</i> and <i>hcnA</i> Altogether, our work demonstrates that the alginate regulators AlgU and AlgR are important in the control of the RsmA posttranscriptional regulatory system. These findings suggest that RsmA plays an unknown role in mucoid strains due to AlgU and AlgR activities.<b>IMPORTANCE</b> <i>P. aeruginosa</i> infections are difficult to treat and frequently cause significant mortality in CF patients. Understanding the mechanisms of persistence is important. Our work has demonstrated that the alginate regulatory system also significantly impacts the posttranscriptional regulator system RsmA/Y/Z. We demonstrate that AlgR directly activates <i>rsmA</i> expression, and this impacts the RsmA regulon. This leads to the possibility that the RsmA/Y/Z system plays a role in helping <i>P. aeruginosa</i> persist during chronic infection. In addition, this furthers our understanding of the reach of the alginate regulators AlgU and AlgR.