Envelope stress response during Salmonella infection:role of σE

Maturana, Pauline. Envelope stress response during Salmonella infection:role of σE. 2020, Doctoral Thesis, University of Basel, Faculty of Science.


Official URL: https://edoc.unibas.ch/78542/

Downloads: Statistics Overview


Bacterial infections are a major public health problem worldwide. Over the years, multi-drug resistant (MDR) pathogens emergence combined with approval absence of new antibiotics in clinics has resulted in untreatable infections. Thus, routine medical procedure constitutes a risk of infection for patients. Therefore, it is crucial to identify novel strategies to efficiently and effectively combat bacterial pathogens.
In vitro, it is challenging to reproduce the microenvironment that pathogens encounter in vivo. Consequently, important stress conditions are omitted, decreasing the ability to identify relevant inhibitor targets. The host immune response largely focuses on the pathogen envelope that constitutes the first line of defense for pathogens and a strong physical barrier. Pathogens possess several envelope stress response systems that enable an adapted response to host attacks, ensuring survival and growth. Inhibiting these systems may enhance host immunity and provide efficient infection control. The extracytoplasmic stress response factor sigma E (E), encoded by rpoE, is crucial for the virulence of several pathogens, including Salmonella. E regulates expression of more than 100 genes, including those that encode proteases, chaperones, and sRNAs to maintain envelope homeostasis. However, it remains unclear which E-regulated gene(s) is (are) critical for in vivo fitness. Here, we used an unbiased approach to identify target mutations that restore ∆rpoE survival by using a transposon library screen. While the parental strain ∆rpoE was cleared from infected mice, several transposon mutants with inactivated ompC survived, indicating partial fitness rescue. Clean mutations (i.e., ∆rpoE ∆ompC) reproduced the transposon effect, confirming the involvement of OmpC in ∆rpoE survival. OmpC could be the entry pore for a toxic molecule whose damages require E-mediated repair. Or, OmpC itself could be or generate a cargo in the periplasm. Further studies are required to understand the exact underlying molecular mechanisms, but the effect of ompC deletion on ∆rpoE fitness is remarkable. Another in vivo screen of the transposon library identified pnp as a target mutation. pnp encodes a major regulator involved in mRNAs degradation and cold shock resistance. Truncated pnp, in combination with ∆rpoE ∆ompC, almost reached WT-like fitness. Surprisingly, in vivo proteomics data demonstrated few differences between WT and mutant bacteria. This suggests that Salmonella can bypass E by a few minor alterations mediated by ompC and pnp deletions.
Collectively, we demonstrate that a small number of mutations can rescue the in vivo fitness of an avirulent regulatory mutant. Synergizing with host studies allows the identification of inhibitor targets that would not be found with our standard in vitro mimicking conditions. We therefore invalidated rpoE as an inhibitor target. Our approach could be more widely used in the future to evaluate other major systems such as the master regulator phoP or the general stress response sigma factor rpoS before potential inhibitors reach the clinics.
Advisors:Bumann, Dirk and Jenal, Urs
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Infection Biology > Molecular Microbiology (Bumann)
UniBasel Contributors:Bumann, Dirk and Jenal, Urs
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:13765
Thesis status:Complete
Number of Pages:102
Identification Number:
  • urn: urn:nbn:ch:bel-bau-diss137657
edoc DOI:
Last Modified:27 Jan 2021 15:57
Deposited On:27 Jan 2021 15:57

Repository Staff Only: item control page