Probing the RyhB-2 regulon in Salmonella Typhimurium

Typically, the expression of sRNAs is activated in response to environmental stimuli in order to regulate gene expression through post-transcriptional mechanisms. In the present work we show that the Salmonella Typhimurium paralog sRNAs RyhB-1 and RyhB-2 are induced in response to the nitrosating agent S-nitrosoglutathione (GSNO). Inactivation of these sRNAs decreased S. Typhimurium resistance to GSNO and increased the levels of nitrosylated proteins. These results prompted us to evaluate a possible role of these sRNAs in nitrosative stress resistance. RNA profiling was used as a screening to identify novel RyhB-1 and RyhB-2 regulated targets, and a subset of genes was filtered based on their potential role in the response to nitrosative stress. To confirm our observation, expression of the candidate targets was analyzed by quantitative RT-PCR in a wild type, single and double mutant strains (ΔryhB1, ΔryhB2 and ΔryhB1 ΔryhB2) treated with GSNO. In response to GSNO RyhB-1 and RyhB-2 negatively regulate the expression of the genes cyoABC (cytochrome o oxidase complex), cydB (cytochrome d oxidase complex), cybC (cytochrome b-562), and positively regulate the nirBCD operon (nitrite reductase system). Together, these results suggest that RyhB-1 and RyhB-2 finely tune the expression of genes coding for cytochrome and the nitrate reductase system, allowing the cell to cope with GSNO-induced stress. Total RNA was harvested from two biological replicates of wt S. Typhimurium overexpressing the sRNA RyhB-2 grown in LB medium, in order to identify RhyB-2 targets that might be implicated in reactive nitrogen stress resistance.