CsrA and its regulators control the time-point of ColicinE2 release in Escherichia coli

TL;DR

This study uncovers how CsrA and its regulators control the timing of ColicinE2 toxin release in E. coli, highlighting the role of ssDNA as a novel regulatory element in toxin secretion.

Contribution

It reveals that CsrA controls the delay between toxin production and release, introducing ssDNA as a new post-transcriptional regulatory element affecting toxin timing.

Findings

CsrA controls the delay in ColicinE2 release.

ssDNA acts as a CsrA sequestering element.

CsrA functions as an ssDNA and mRNA-binding protein.

Abstract

The bacterial SOS response is a cellular reaction to DNA damage, that, among other actions, triggers the expression of colicin - toxic bacteriocins in Escherichia coli that are released to kill close relatives competing for resources. However, it is largely unknown, how the complex network regulating toxin expression controls the time-point of toxin release to prevent premature release of inefficient protein concentrations. Here, we study how different regulatory mechanisms affect production and release of the bacteriocin ColicinE2 in Escherichia coli. Combining experimental and theoretical approaches, we demonstrate that the global carbon storage regulator CsrA controls the duration of the delay between toxin production and release and emphasize the importance of CsrA sequestering elements for the timing of ColicinE2 release. In particular, we show that ssDNA originating from rolling-circle replication of the toxin-producing plasmid represents a yet unknown additional CsrA sequestering element, which is essential in the ColicinE2-producing strain to enable toxin release by reducing the amount of free CsrA molecules in the bacterial cell. Taken together, our findings show that CsrA times ColicinE2 release and reveal a dual function for CsrA as an ssDNA and mRNA-binding protein, introducing ssDNA as an important post-transcriptional gene regulatory element.