Biofilm formation-gene expression relay system in Escherichia coli: modulation of sigma(S)-dependent gene expression by the CsgD regulatory protein via sigma(S) protein stabilization

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 (sigmaS) regulon. Protein pattern analysis of E. coli cells in stationary phase shows that CsgD affects the expression of several proteins encoded by sigmaS-dependent genes. CsgD regulation of sigmaS-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 sigmaS intracellular concentration. Increase in sigmaS cellular amount is mediated by CsgD-dependent transcription activation of iraP, encoding a factor involved in sigmaS protein stabilization. Our results strongly suggest that the CsgD regulatory protein plays a major role as a relay between adhesion factors production and sigmaS-dependent gene expression via sigmaS 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.