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J. Bacteriol. doi:10.1128/JB.01443-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Analysis of secretin-induced stress in Pseudomonas aeruginosa suggests prevention rather than response and identifies a novel protein involved in secretin function

Department of Microbiology, New York University School of Medicine, New York, NY 10016; and Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115

^* To whom correspondence should be addressed. Email: andrew.darwin{at}med.nyu.edu.

	Abstract

Secretins are bacterial outer membrane proteins important for protein export. However, they can also mislocalize and cause stress to the bacterial cell, which is dealt with by the well-conserved phage-shock-protein (Psp) system in a highly specific manner. Nevertheless, some bacteria have secretins but no Psp system. A notable example is Pseudomonas aeruginosa, a prolific protein secretor with the potential to produce seven different secretins. We were interested to investigate how P. aeruginosa might deal with the potential for secretin-induced stress without a Psp system. Microarray analysis revealed the absence of any transcriptional response to XcpQ secretin overproduction. However, transposon insertions in either rpoN, truB, PA4068, PA4069 or PA0943 rendered P. aeruginosa hypersensitive to XcpQ production. The PA0943 gene was studied further and found to encode a soluble periplasmic protein important for XcpQ localization to the outer membrane. Consistent with this, a PA0943 null mutation reduced the levels of type 2 secretion-dependent proteins in the culture supernatant. Therefore, this work has identified a novel protein required for normal secretin function in P. aeruginosa. Taken together, all of our data suggests that P. aeruginosa lacks a functional equivalent of the Psp stress-response system. Rather, null mutations in genes such as PA0943 may cause increased secretin-induced stress to which P. aeruginosa cannot respond. Providing the PA0943 mutant with the ability to respond, in the form of critical Psp proteins from another species, alleviated its secretin-sensitivity.