Implication of the σ

Area of Science:

• Bacterial outer membrane protein structure and function
• Microbial stress response mechanisms
• Genomic and transcriptomic analysis in bacteria

Background:

• Outer membrane protein A (OmpA) is vital for bacterial cell envelope integrity.
• A Stenotrophomonas maltophilia mutant lacking the OmpA C-terminal domain (KJΔOmpA299-356) shows reduced tolerance to oxidative stress.
• The precise mechanism behind this decreased tolerance remains to be fully elucidated.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the reduced menadione-mediated oxidative stress tolerance in the Stenotrophomonas maltophilia KJΔOmpA299-356 mutant.
• To identify key genes and regulatory factors involved in the stress response pathway affected by OmpA C-terminal domain loss.
• To elucidate the regulatory circuit connecting OmpA function, σ factor activity, and oxidative stress tolerance.

Main Methods:

• Comparative transcriptome analysis of wild-type and KJΔOmpA299-356 Stenotrophomonas maltophilia strains.
• Gene complementation assays to validate the role of specific genes (e.g., ompO) in stress tolerance.
• Analysis of σ factor expression levels (rpoN, rpoP, rpoE) in response to OmpA mutation.
• Construction and characterization of mutant strains for individual σ factors to assess their contribution to stress tolerance.

Main Results:

• The ompO gene was significantly downregulated in the KJΔOmpA299-356 mutant, and its complementation restored menadione tolerance.
• Expression of three σ factors, rpoN (downregulated), rpoP (upregulated), and rpoE (upregulated), was altered in the mutant.
• Downregulation of rpoN and upregulation of rpoE were identified as key contributors to the decreased oxidative stress tolerance.
• Loss of the OmpA C-terminal domain triggered an envelope stress response, leading to σE activation, which in turn reduced rpoN and ompO expression.

Conclusions:

• The OmpA C-terminal domain is critical for maintaining oxidative stress tolerance in Stenotrophomonas maltophilia.
• A regulatory circuit involving the ΔompA299-356 mutant, rpoE, and ompO mediates changes in oxidative stress tolerance.
• Cross-regulation between rpoE and rpoN plays a significant role in the observed stress response phenotypes.
• OmpA's interaction with the peptidoglycan layer is essential for envelope integrity and bacterial stress tolerance.