Dual role of CsrA in regulating the hemolytic activity of Escherichia coli O157:H7

ABSTRACT

Post-transcriptional global carbon storage regulator A (CsrA) is a sequence-specific RNA-binding protein involved in the regulation of multiple bacterial processes. Hemolysin is an important virulence factor in the enterohemorrhagic Escherichia coli O157:H7 (EHEC). Here, we show that CsrA plays a dual role in the regulation of hemolysis in EHEC. CsrA significantly represses plasmid-borne enterohemolysin (EhxA)-mediated hemolysis and activates chromosome-borne hemolysin E (HlyE)-mediated hemolysis through different mechanisms. RNA structure prediction revealed a well-matched stem-loop structure with two potential CsrA binding sites located on the 5' untranslated region (UTR) of ehxB, which encodes a translocator required for EhxA secretion. CsrA inhibits EhxA secretion by directly binding to the RNA leader sequence of ehxB to repress its expression in two different ways: CsrA either binds to the Shine–Dalgarno sequence of ehxB to block ribosome access or to ehxB transcript to promote its mRNA decay. The predicted CsrA-binding site 1 of ehxB is essential for its regulation. There is a single potential CsrA-binding site at the 5'-end of the hlyE transcript, and its mutation completely abolishes CsrA-dependent activation. CsrA can also stabilize hlyE mRNA by directly binding to its 5' UTR. Overall, our results indicate that CsrA acts as a hemolysis modulator to regulate pathogenicity under certain conditions.

KEYWORDS:

• Escherichia coli O157:H7
• hemolysis
• CsrA/RsmA
• virulence
• protein–RNA interaction

Acknowledgment

We thank Prof. Rahul V. Kulkarni at the University of Massachusetts, Boston, for providing the computer code (CSRA_TARGET) for CsrA-binding site prediction.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/21505594.2022.2073023.

Additional information

Funding

This work was supported by grants from the National Natural Science Foundation of China [Nos. 81902035, 81830068, and 81772140], Key Research and Development Project of China [No.2016YFA0500600], GuangCi Professorship Program of Ruijin Hospital Shanghai Jiao Tong University School of Medicine, the State Key Development Programs for Basic Research of China [973 Program No. 2015CB554203], the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, China Postdoctoral Science Foundation [2018M630447], and Key R&D Program of Jiangsu Province [BE2020707].