JB Accepts, published online ahead of print on 29 September 2006

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J. Bacteriol. doi:10.1128/JB.00157-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The effect of site-specific mutations in different phosphotransfer domains of the chemosensory protein ChpA on Pseudomonas aeruginosa motility

Andrew J. Leech and John S. Mattick^*

Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD 4072, Australia

^* To whom correspondence should be addressed. Email: j.mattick{at}imb.uq.edu.au.

Virulence of Pseudomonas aeruginosa and other surface pathogens involves the coordinate expression of a wide range of virulence determinants, including type IV pili. These surface filaments are important for colonization of host epithelial tissues and mediate bacterial attachment to, and translocation across, surfaces by a process known as twitching motility. This process is controlled in part by a complex signal transduction system whose central component ChpA possesses nine potential sites of phosphorylation, including six histidine-containing phosphotransfer (HPt) domains, one serine- and one threonine-containing phosphotransfer (SPt, TPt) domain, and one CheY-like receiver domain. Here, we show using site-directed mutagenesis that normal twitching motility is entirely dependent on the CheY-like receiver domain, and partially dependent on two of the HPt domains. Moreover, under different assay conditions, point mutations in several of the phosphotransfer domains of ChpA give rise to unusual "swarming" phenotypes, possibly reflecting more subtle perturbations in the control of P. aeruginosa motility that are not evident from the conventional twitching stab assay. Together, these results suggest that ChpA plays a central role in the complex regulation of type IV pili-mediated motility in P. aeruginosa.

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