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Journal of Bacteriology, March 2009, p. 1695-1702, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01536-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Growth Phase- and Cell Division-Dependent Activation and Inactivation of the {sigma}32 Regulon in Escherichia coli{triangledown} ,{dagger}

Maria Anna Wagner, Doris Zahrl,{ddagger} Gernot Rieser, and Günther Koraimann*

Institut für Molekulare Biowissenschaften, Karl-Franzens-Universität Graz, Humboldtstrasse 50, A-8010 Graz, Austria

Received 30 October 2008/ Accepted 16 December 2008

Alternative sigma factors allow bacteria to reprogram global transcription rapidly and to adapt to changes in the environment. Here we report on growth- and cell division-dependent {sigma}32 regulon activity in Escherichia coli in batch culture. By analyzing {sigma}32 expression in growing cells, an increase in {sigma}32 protein levels is observed during the first round of cell division after exit from stationary phase. Increased {sigma}32 protein levels result from transcriptional activation of the rpoH gene. After the first round of bulk cell division, rpoH transcript levels and {sigma}32 protein levels decrease again. The late-logarithmic phase and the transition to stationary phase are accompanied by a second increase in {sigma}32 levels and enhanced stability of {sigma}32 protein but not by enhanced transcription of rpoH. Throughout growth, {sigma}32 target genes show expression patterns consistent with oscillating {sigma}32 protein levels. However, during the transition to early-stationary phase, despite high {sigma}32 protein levels, the transcription of {sigma}32 target genes is downregulated, suggesting functional inactivation of {sigma}32. It is deduced from these data that there may be a link between {sigma}32 regulon activity and cell division events. Further support for this hypothesis is provided by the observation that in cells in which FtsZ is depleted, {sigma}32 regulon activation is suppressed.

* Corresponding author. Mailing address: Institut für Molekulare Biowissenschaften, Karl-Franzens-Universität Graz, Humboldtstrasse 50, A-8010 Graz, Austria. Phone: 43 (316) 380 5620. Fax: 43 (316) 380 9898. E-mail: guenther.koraimann{at}uni-graz.at

{triangledown} Published ahead of print on 29 December 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Roche Diagnostics Graz GmbH, Kratkystrasse 2, A-8020 Graz, Austria.

Journal of Bacteriology, March 2009, p. 1695-1702, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01536-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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