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Pseudomonas aeruginosa is an opportunistic pathogen that is capable of causing both acute and chronic infections. P. aeruginosa virulence is subject to sophisticated regulatory control by two-component systems that enable it to sense and respond to environmental stimuli. We recently reported that the two-component sensor KinB regulates virulence in acute P. aeruginosa infection. Furthermore, it regulates acute-virulence-associated phenotypes such as pyocyanin production, elastase production, and motility in a manner independent of its kinase activity. Here we show that KinB regulates virulence through the global sigma factor AlgU, which plays a key role in repressing P. aeruginosa acute-virulence factors, and through its cognate response regulator AlgB. However, we show that rather than phosphorylating AlgB, KinB's primary role in the regulation of virulence is to act as a phosphatase to dephosphorylate AlgB and alleviate phosphorylated AlgB's repression of acute virulence.