Activation of regulator ArcA in the presence of hypochlorite in Salmonella enterica serovar Typhimurium.

Oxidative stress is the main mechanism behind efficient disinfectants, causing damage in bacterial macromolecules. Importantly, bacteria activate resistance mechanisms in response to damage generated by oxidative stress. Strategies allowing pathogens to survive oxidative stress are highly conserved among microorganisms. Many of these strategies entail genomic responses triggered by signals transduced through Two Component Systems (TCS). Recently, we demonstrated that the TCS ArcAB (specifically ArcA) participates in bacterial responses to hypochlorite, regulating the uptake of this toxic compound and being involved in resistance and survival inside neutrophils, where hypochlorous acid abounds. Here, we demonstrated that ArcA is required in the response to oxidative stress generated by hypochlorite, independent of its cognate sensor ArcB or the Asp54 of ArcA, the only phosphorylable residue in ArcA, which is required to function as a gene regulator. Our results suggest that ArcA could have additional functions to respond to oxidative stress, independent of its regulatory activity, which might require interaction with other unknown relevant proteins.

Correction: The ArcAB two-component regulatory system promotes resistance to reactive oxygen species and systemic infection by Salmonella Typhimurium.

[This corrects the article DOI: 10.1371/journal.pone.0203497.].

The ArcAB two-component regulatory system promotes resistance to reactive oxygen species and systemic infection by Salmonella Typhimurium.

Salmonella enterica Serovar Typhimurium (S. Typhimurium) is an intracellular bacterium that overcomes host immune system barriers for successful infection. The bacterium colonizes the proximal small intestine, penetrates the epithelial layer, and is engulfed by macrophages and neutrophils. Intracellularly, S. Typhimurium encounters highly toxic reactive oxygen species including hydrogen peroxide and hypochlorous acid. The molecular mechanisms of Salmonella resistance to intracellular oxidative stress is not completely understood. The ArcAB two-component system is a global regulatory system that responds to oxygen. In this work, we show that the ArcA response regulator participates in Salmonella adaptation to changing oxygen levels and is also involved in promoting intracellular survival in macrophages and neutrophils, enabling S. Typhimurium to successfully establish a systemic infection.

The transcription factor SlyA from Salmonella Typhimurium regulates genes in response to hydrogen peroxide and sodium hypochlorite.

Salmonella Typhimurium is an intracellular pathogen that is capable of generating systemic fever in a murine model. Over the course of the infection, Salmonella faces different kinds of stressors, including harmful reactive oxygen species (ROS). Various defence mechanisms enable Salmonella to successfully complete the infective process in the presence of such stressors. The transcriptional factor SlyA is involved in the oxidative stress response and invasion of murine macrophages. We evaluated the role of SlyA in response to H2O2 and NaOCl and found an increase of slyA expression upon exposure to these toxics. However, the SlyA target genes and the molecular mechanisms by which they influence the infective process are unknown. We hypothesised that SlyA regulates the expression of genes required for ROS resistance, metabolism, or virulence under oxidative stress conditions. Transcriptional profiling in wild type and ΔslyA strains confirmed that SlyA regulates the expression of several genes involved in virulence [sopD (STM14_3550), sopE2 (STM14_2244), hilA (STM14_3475)] and central metabolism [kgtP (STM14_3252), fruK (STM14_2722), glpA (STM14_2819)] in response to H2O2 and NaOCl. These findings were corroborated by functional assay and transcriptional fusion assays using GFP. DNA-protein interaction assays showed that SlyA regulates these genes through direct interaction with their promoter regions.