Role of Salmonella Typhimurium small RNAs RyhB-1 and RyhB-2 in the oxidative stress response

As part of the response to specific stress conditions, bacteria express small molecules of non-coding RNA which maintain cellular homeostasis by regulating gene expression, commonly at the post-transcriptional level. Among these, in Salmonella enterica sv. Typhimurium, the paralog small non-coding RNAs RyhB-1 and RyhB-2 play an important role in iron homeostasis. In addition, in the present work, we show that RyhB-1 and RyhB-2 also participate in the response to hydrogen peroxide (H₂O₂). Deletion of RyhB-1 and/or RyhB-2 resulted in increased levels of intracellular reactive oxygen species, protein carbonylation and an altered NADH/NAD⁺ ratio. Analyses of the transcriptional profiles of ryhB-1 and ryhB-2 by northern blot and qRT-PCR showed that they are induced in response to H₂O₂ in an OxyR-dependent manner. By using lacZ-fusions and electrophoretic mobility shift assays, we confirmed the requirement of OxyR for inducing expression of both ryhB-1 and ryhB-2. Taken together, our results support a model in which, in response to peroxide treatment, ryhB-1 and ryhB-2 are upregulated by OxyR through direct interaction with their promoter region.