Characterization of a novel post-transcriptional regulator in P. aeruginosa

Abstract Pseudomonas aeruginosa is an important opportunistic pathogen of humans. It is the principal cause of morbidity and mortality in people with cystic fibrosis, is a major cause of hospital-acquired pneumonia and is particularly problematic in chronic wound infections. Post-transcriptional regulators are known to play important roles in controlling the virulence of P. aeruginosa and the best characterized of these are the RNA-binding proteins Hfq and RsmA. However, apart from these two regulators, little is known about the roles played by other RNA-binding proteins in this gram-negative bacterium. Here we propose to study a putative RNA-binding protein in P. aeruginosa called PhaF that we have recently found to be a global post-transcriptional regulator. In Aim 1 we propose to identify the direct regulatory targets of PhaF in P. aeruginosa strain PAO1, a commonly used laboratory strain, at different phases of growth and investigate the activity of PhaF in clinical isolates of P. aeruginosa. We will also identify PhaF target transcripts in cells grown under conditions that more closely mimic infection conditions, as well as in an animal model of chronic infection. In addition, we propose to test whether PhaF influences the virulence of P. aeruginosa through its effects on several of the targets we have already identified that are linked to biofilm formation and virulence. These experiments will help better define the PhaF regulon under standard laboratory growth conditions, as well as conditions that are relevant to infections. Furthermore, they will provide the first assessment of the extent to which the PhaF regulon is conserved between laboratory strains of P. aeruginosa and clinical isolates. The putative RNA-binding domain present in the C- terminal domain (CTD) of PhaF is remarkable in that it contains 20 or more repeats of the motif KPAA found in histone H1 from eukaryotes. In Aim 2 we will determine whether the CTD of PhaF constitutes a novel RNA- binding determinant, investigate the mechanism by which PhaF positively regulates the translation of target transcripts, and determine what governs the apparent switch in PhaF target specificity that occurs in response to varying growth conditions. Our studies are expected to illuminate the regulatory roles and mechanism of action of a newly identified global post-transcriptional regulator that controls the expression of important determinants of biofilm formation and virulence in P. aeruginosa. The experiments we describe are relevant for understanding post-transcriptional control exerted by RNA-binding proteins in clinical isolates of this bacterium.