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Biofilm Formation-Gene Expression Relay System in Escherichia coli: Modulation of ^S-Dependent Gene Expression by the CsgD Regulatory Protein via ^S Protein Stabilization ^,

Department of Biomolecular Sciences and Biotechnology, University of Milan, Via Celoria 26, 20133 Milan, Italy

Received 8 June 2007/ Accepted 4 September 2007

Bacteria can switch from a single-cell (planktonic) mode to a multicellular community (biofilm) mode via production of cell-cell aggregation and surface adhesion factors. In this report, we present evidence that the CsgD protein, a transcription regulator involved in biofilm formation in Escherichia coli, modulates the expression of the rpoS (^S) regulon. Protein pattern analysis of E. coli cells in stationary phase shows that CsgD affects the expression of several proteins encoded by ^S-dependent genes. CsgD regulation of ^S-dependent genes takes place at gene transcription level, does not bypass the need for rpoS, and is abolished in an rpoS-null mutant. Consistent with these results, we find that CsgD expression leads to an increase in ^S intracellular concentration. Increase in ^S cellular amount is mediated by CsgD-dependent transcription activation of iraP, encoding a factor involved in ^S protein stabilization. Our results strongly suggest that the CsgD regulatory protein plays a major role as a relay between adhesion factors production and ^S-dependent gene expression via ^S protein stabilization. Direct coordination between biofilm formation and expression of the rpoS regulon could positively impact important biological processes, such as host colonization or response to environmental stresses.

Published ahead of print on 14 September 2007.

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