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J. Bacteriol. doi:10.1128/JB.00900-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A 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

^* To whom correspondence should be addressed. Email: paolo.landini{at}unimi.it.

	Abstract

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 by-pass 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 co-ordination between biofilm formation and expression of the rpoS regulon could positively impact important biological processes, such as host colonization or response to environmental stresses.

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