Small RNAs in the control of RpoS, CsgD, and biofilm architecture of Escherichia coli

Abstract

Amyloid curli fibers and cellulose are extracellular matrix components produced in the stationary phase top layer of E. coli macrocolonies, which confer physical protection, strong cohesion, elasticity, and wrinkled morphology to these biofilms. Curli and cellulose synthesis is controlled by a three-level transcription factor (TF) cascade with the RpoS sigma subunit of RNA polymerase at the top, the MerR-like TF MlrA, and the biofilm regulator CsgD, with two c-di-GMP control modules acting as key switching devices. Additional signal input and fine-tuning is provided by an entire series of small RNAs—ArcZ, DsrA, RprA, McaS, OmrA/OmrB, GcvB, and RydC—that differentially control all three TF modules by direct mRNA interaction. This review not only summarizes the mechanisms of action of these sRNAs, but also addresses the question of how these sRNAs and the regulators they target contribute to building the intriguing three-dimensional microarchitecture and macromorphology of these biofilms.

Keywords: :

• ArcZ
• biofilm
• c-di-GMP
• cellulose
• CsgD
• curli
• Hfq
• McaS
• RpoS
• RprA

^{Submitted: 02/16/2014; Revised: 04/10/2014; Accepted: 04/12/2014}

^{10.4161/rna.28867}

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We thank our colleague and coworker Diego O Serra for contributing Figure 1 and the scanning EM image integrated in Figure 3. Research on sRNAs and biofilm regulation in the Hengge laboratory has been funded by the Deutsche Forschungsgemeinschaft (He 1556/14) and the European Research Council under the European Unions Seventh Framework Programme (ERC-AdG 249780 to Hengge R).