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Journal of Bacteriology, August 2008, p. 5567-5575, Vol. 190, No. 16
0021-9193/08/$08.00+0     doi:10.1128/JB.00577-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Fur-Dependent Detoxification of Organic Acids by rpoS Mutants during Prolonged Incubation under Aerobic, Phosphate Starvation Conditions{triangledown}

Mélanie L. Guillemet and Patrice L. Moreau*

Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, 13009 Marseille, France

Received 25 April 2008/ Accepted 9 June 2008

The activity of amino acid-dependent acid resistance systems allows Escherichia coli to survive during prolonged incubation under phosphate (Pi) starvation conditions. We show in this work that rpoS-null mutants incubated in the absence of any amino acid survived during prolonged incubation under aerobic, Pi starvation conditions. Whereas rpoS+ cells incubated with glutamate excreted high levels of acetate, rpoS mutants grew on acetic acid. The characteristic metabolism of rpoS mutants required the activity of Fur (ferric uptake regulator) in order to decrease the synthesis of the small RNA RyhB that might otherwise inhibit the synthesis of iron-rich proteins. We propose that RpoS ({sigma}S) and the small RNA RyhB contribute to decrease the synthesis of iron-rich proteins required for the activity of the tricarboxylic acid (TCA) cycle, which redirects the metabolic flux toward the production of acetic acid at the onset of stationary phase in rpoS+ cells. In contrast, Fur activity, which represses ryhB, and the lack of RpoS activity allow a substantial activity of the TCA cycle to continue in stationary phase in rpoS mutants, which decreases the production of acetic acid and, eventually, allows growth on acetic acid and Pi excreted into the medium. These data may help explain the fact that a high frequency of E. coli rpoS mutants is found in nature.

* Corresponding author. Mailing address: CNRS-LCB, 31 chemin Joseph Aiguier, 13009 Marseille, France. Phone: (33) 4 91 16 43 53. Fax: (33) 4 91 71 89 14. E-mail: moreau{at}ibsm.cnrs-mrs.fr

{triangledown} Published ahead of print on 13 June 2008.

Journal of Bacteriology, August 2008, p. 5567-5575, Vol. 190, No. 16
0021-9193/08/$08.00+0     doi:10.1128/JB.00577-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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