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Journal of Bacteriology, September 2006, p. 6611-6621, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00632-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Expression and Assembly of a Functional Type IV Secretion System Elicit Extracytoplasmic and Cytoplasmic Stress Responses in Escherichia coli

Doris Zahrl, Maria Wagner, Karin Bischof, and Günther Koraimann*

Institut für Molekulare Biowissenschaften (IMB), Karl-Franzens-Universität Graz, Universitätsplatz 2, A-8010 Graz, Austria

Received 4 May 2006/ Accepted 7 July 2006

Conditions perturbing protein homeostasis are known to induce cellular stress responses in prokaryotes and eukaryotes. Here we show for the first time that expression and assembly of a functional type IV secretion (T4S) machinery elicit extracytoplasmic and cytoplasmic stress responses in Escherichia coli. After induction of T4S genes by a nutritional upshift and assembly of functional DNA transporters encoded by plasmid R1-16, host cells activated the CpxAR envelope stress signaling system, as revealed by induction or repression of downstream targets of the CpxR response regulator. Furthermore, we observed elevated transcript levels of cytoplasmic stress genes, such as groESL, with a concomitant increase of {sigma}32 protein levels in cells expressing T4S genes. A traA null mutant of plasmid R1-16, which lacks the functional gene encoding the major pilus protein pilin, showed distinctly reduced stress responses. These results corroborated our conclusion that the activation of bacterial stress networks was dependent on the presence of functional T4S machinery. Additionally, we detected increased transcription from the rpoHp1 promoter in the presence of an active T4S system. Stimulation of rpoHp1 was dependent on the presence of CpxR, suggesting a hitherto undocumented link between CpxAR and {sigma}32-regulated stress networks.

* Corresponding author. Mailing address: Institut für Molekulare Biowissenschaften (IMB), Karl-Franzens-Universität Graz, Universitätsplatz 2, A-8010 Graz, Austria. Phone: 43 (316) 380 5620. Fax: 43 (316) 380 9898. E-mail: guenther.koraimann{at}uni-graz.at.

Journal of Bacteriology, September 2006, p. 6611-6621, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00632-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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