Genetic regulation of the ompX porin of Salmonella Typhimurium in response to hydrogen peroxide stress

A C Briones,A A Hidalgo,M Espinoza,A Cofre,C E Cabezas,M S Baquedano,G I Krüger,E H Morales,J Castro-Severyn,C Pardo-Esté,D Lorca,F Remonsellez,C R Salinas,C P Saavedra

doi:10.1186/s40659-022-00377-3

A C Briones, A A Hidalgo + Show 12 more

Open Access

https://doi.org/10.1186/s40659-022-00377-3

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Abstract

BackgroundSalmonella Typhimurium is a Gram-negative pathogen that causes a systemic disease in mice resembling typhoid fever. During its infective cycle, S. Typhimurium is phagocytized by macrophages and proliferates inside a Salmonella-containing vacuole where Salmonella is exposed and survives oxidative stress induced by H2O2 through modulation of gene expression. After exposure of Salmonella to H2O2, the expression of the porin-encoding gene ompX increases, as previously shown by microarray analysis. Expression of ompX mRNA is regulated at a post-transcriptional level by MicA and CyaR sRNAs in aerobiosis. In addition, sequence analysis predicts a site for OxyS sRNA in ompX mRNA.ResultsIn this work we sought to evaluate the transcriptional and post-transcriptional regulation of ompX under H2O2 stress. We demonstrate that ompX expression is induced at the transcriptional level in S. Typhimurium under such conditions. Unexpectedly, an increase in ompX gene transcript and promoter activity after challenges with H2O2 does not translate into increased protein levels in the wild-type strain, suggesting that ompX mRNA is also regulated at a post-transcriptional level, at least under oxidative stress. In silico gene sequence analysis predicted that sRNAs CyaR, MicA, and OxyS could regulate ompX mRNA levels. Using rifampicin to inhibit mRNA expression, we show that the sRNAs (MicA, CyaR and OxyS) and the sRNA:mRNA chaperone Hfq positively modulate ompX mRNA levels under H2O2-induced stress in Salmonella during the exponential growth phase in Lennox broth.ConclusionsOur results demonstrate that ompX mRNA is regulated in response to H2O2 by the sRNAs CyaR, MicA and OxyS is Salmonella Typhimurium.

Highlights

Every year, Salmonella enterica causes around 1800 food-borne illness cases in the United States, resulting in about 200 hospitalizations
Our results show that Outer membrane porin X (ompX) transcript levels increase under peroxide stress, yet there are no changes at the protein level under the same conditions
To investigate whether the observed increase in ompX Messenger Ribonucleic Acid (mRNA) and promoter activity levels correlated with higher protein levels, we measured the OmpX protein by immunoblot

Summary

Introduction

Salmonella enterica causes around 1800 food-borne illness cases in the United States, resulting in about 200 hospitalizations. Salmonella survives within innate immune host cells, including macrophages [37], where bacteria are exposed to adverse conditions that limit its survival. ROS generated by phagocytic cells, superoxide anions (O2−) and hydrogen peroxide (H2O2), target bacterial components such as proteins, membranes, and nucleic acids [21]. Typhimurium is phagocytized by macrophages and proliferates inside a Salmonella-containing vacuole where Salmonella is exposed and survives oxidative stress induced by H 2O2 through modulation of gene expression. After exposure of Salmonella to H 2O2, the expression of the porin-encoding gene ompX increases, as previously shown by microarray analysis. Expression of ompX mRNA is regulated at a posttranscriptional level by MicA and CyaR sRNAs in aerobiosis. Sequence analysis predicts a site for OxyS sRNA in ompX mRNA

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