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

Background Salmonella 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 H 2 O 2 through modulation of gene expression. After exposure of Salmonella to H 2 O 2 , 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. Results In this work we sought to evaluate the transcriptional and post-transcriptional regulation of ompX under H 2 O 2 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 H 2 O 2 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 H 2 O 2 -induced stress in Salmonella during the exponential growth phase in Lennox broth. Conclusions Our results demonstrate that ompX mRNA is regulated in response to H 2 O 2 by the sRNAs CyaR, MicA and OxyS is Salmonella Typhimurium.