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Mol Microbiol. 2011 Jan;79(1):264-78. doi: 10.1111/j.1365-2958.2010.07444.x. Epub 2010 Nov 17.

Continuous control of flagellar gene expression by the σ28-FlgM regulatory circuit in Salmonella enterica.

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Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.


The flagellar genes in Salmonella enterica are expressed in a temporal hierarchy that mirrors the assembly process itself. The σ(28)-FlgM regulatory circuit plays a key role in controlling this temporal hierarchy. This circuit ensures that the class 3 genes are expressed only when the hook-basal body (HBB), a key intermediate in flagellar assembly, is complete. In this work, we investigated the role of the σ(28)-FlgM regulatory circuit in controlling the timing and magnitude of class 3 gene expression using a combination of mathematical modelling and experimental analysis. Analysis of the model predicted that this circuit continuously controls class 3 gene expression in response to HBB abundance. We experimentally validated these predictions by eliminating different components of the σ(28)-FlgM regulatory system and also by rewiring the transcriptional hierarchy. Based on these results, we conclude that the σ(28)-FlgM regulatory circuit continuously senses the HBB assembly process and regulates class 3 gene expression and possibly flagellar numbers in response.

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