Role of the ArcAB two-component system in oxidative stress

Salmonella enterica serovar Typhimurium is a Gram-negative bacterium, facultative anaerobe and intracellular pathogen that causes enteric fever in mice. Once orally ingested, Salmonella invades and traverse the mucosal intestinal epithelia, where it is phagocytized by specialized cells including macrophages, dendritic cells and neutrophils. Within these cells, the bacterium is kept in a compartment termed Salmonella containing vacuole where it is exposed to different adverse conditions including nutrient deprivation, acid pH, reactive oxygen (ROS) as well as nitrogen (RNS) species and low oxygen levels. Among the signals encountered by the bacteria, oxidative stress is one of the main challenges that it has to overcome in order to survive. In this context, the OxyR and SoxRS proteins are the most studied regulators involved in response to ROS. However, in the past years growing evidence suggests that the ArcAB two-component system might play a key role in modulating gene expression in response to ROS. Furthermore, the global regulator ArcA is required for the resistance of Escherichia coli, S. Enteritidis and Typhimurium to hydrogen peroxide (H2O2), however, the ArcA regulon under oxidative stress conditions remains elusive. Therefore, the aim of this work was to demonstrate that ArcAB regulates the expression of genes in response to hydrogen peroxide and determine the ArcA regulon under this condition. To achieve this, we evaluated transcriptomic changes in strain 14028s, ∆arcA in response to H2O2. Total RNA was harvested from three biological replicates of wt and arcA mutant cultures exposed or unexposed to 1.5 mM hydrogen peroxide for 20 min in LB medium.