Nitric Oxide Disrupts Zinc Homeostasis in Salmonella enterica Serovar Typhimurium

Nitric oxide (NO center dot) produced by mammalian cells exerts antimicrobial actions that result primarily from the modification of protein thiols (S-nitrosylation) and metal centers. A comprehensive approach was used to identify novel targets of Na in Salmonella enterica serovar Typhimurium (S. Typhimurium). Newly identified targets include zinc metalloproteins required for DNA replication and repair (DnaG, PriA, and TopA), protein synthesis (AlaS and RpmE), and various metabolic activities (CIpX, GloB, MetE, PepA, and QueC). The cytotoxic actions of free zinc are mitigated by the ZntA and ZitB zinc efflux transporters, which are required for S. Typhimurium resistance to zinc overload and nitrosative stress in vitro. Zinc efflux also ameliorates NO center dot-dependent zinc mobilization following internalization by activated macrophages and is required for virulence in NO center dot-producing mice, demonstrating that hostderived NO center dot causes zinc stress in intracellular bacteria. IMPORTANCE Nitric oxide (NO center dot) is produced by macrophages in response to in-CO flammatory stimuli and restricts the growth of intracellular bacteria. Mechanisms of NO center dot-dependent antimicrobial actions are incompletely understood. Here, we show that zinc metalloproteins are important targets of NO center dot in Salmonella, including the DNA replication proteins DnaG and PriA, which were hypothesized to be NO center dot targets in earlier studies. Like iron, zinc is a cofactor for several essential proteins but is toxic at elevated concentrations. This study demonstrates that NO center dot mobilizes free zinc in Salmonella and that specific efflux transporters ameliorate the cytotoxic effects of free zinc during infection.