The Prc and CtpA proteases modulate cell-surface signaling activity and virulence in Pseudomonas aeruginosa

Cell-surface signaling (CSS) is a signal transfer system of Gram-negative bacteria that produces the activation of an extracytoplasmic function σ factor (σ^ECF) in the cytosol in response to an extracellular signal. Activation requires the regulated and sequential proteolysis of the σ^ECF-associated anti-σ factor, and the function of the Prc and RseP proteases. In this work, we have identified another protease that modulates CSS activity, namely the periplasmic carboxyl-terminal processing protease CtpA. CtpA functions upstream of Prc in the proteolytic cascade and seems to prevent the Prc-mediated proteolysis of the CSS anti-σ factor. Importantly, using zebrafish embryos and the A549 lung epithelial cell line as hosts, we show that mutants in the rseP and ctpA proteases of the human pathogen Pseudomonas aeruginosa are considerably attenuated in virulence while the prc mutation increases virulence likely by enhancing the production of membrane vesicles.