Abstract
To colonize in the digestive tract of animals and humans, Yersinia pseudotuberculosis has to deal with reactive oxygen species (ROS) produced by host cells and microbiota. However, an understanding of the ROS-scavenging systems and their regulation in this bacterium remains largely elusive. In this study, we identified OxyR as the master transcriptional regulator mediating cellular responses to hydrogen peroxide (H2O2) in Y. pseudotuberculosis through genomics and transcriptomics analyses. OxyR activates transcription of diverse genes, especially the core members of its regulon, including those encoding catalases, peroxidases, and thiol reductases. The data also suggest that sulfur species and manganese may play a particular role in the oxidative stress response of Y. pseudotuberculosis. Among the three H2O2-scavenging systems in Y. pseudotuberculosis, catalase/peroxidase KatE functions as the primary scavenger for high levels of H2O2; NADH peroxidase alkyl hydroperoxide reductase (AhpR) and catalase KatG together are responsible for removing low levels of H2O2. The simultaneous loss of both AhpC (the peroxidatic component of AhpR) and KatG results in activation of OxyR. Moreover, we found that AhpC, unlike its well-characterized Escherichia coli counterpart, has little effect on protecting cells against toxicity of organic peroxides. These findings provide not only novel insights into the structural and functional diversity of bacterial H2O2-scavenging systems but also a basic understanding of how Y. pseudotuberculosis copes with oxidative stress.
Highlights
Oxidative stress caused by reactive oxygen species (ROS), including superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl radical (OH·), is inevitable to all organisms that respire oxygen (Li et al, 2016)
alkyl hydroperoxide reductase (AhpR) typically consists of two cytoplasmic proteins encoded by a single operon, the peroxidase component AhpC and its cognate reductase AhpF: the former is a bacterial representative of typical 2-Cys peroxiredoxins and the latter is a flavoprotein with NADH:disulfide oxidoreductase activity (Poole, 2005)
The sequence similarities between YpOxyR and dual-activity OxyRs, such as that of S. oneidensis, are substantially lower (E-value = 7e-47; identities, 33%; Supplementary Figure 2), implying that YpOxyR might function as an activator only
Summary
Oxidative stress caused by reactive oxygen species (ROS), including superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl radical (OH·), is inevitable to all organisms that respire oxygen (Li et al, 2016). Oxidative Stress Response of Y. pseudotuberculosis enters into cells nearly freely, where it reacts with Fe2+ to generate most deadly hydroxyl radicals (Li et al, 2016) Because of these features, most bacteria employ multiple enzymes, including catalases, various peroxidases, and rubrerythrin, to keep the intracellular concentrations of H2O2 at safe limit (nanomolar levels; Mishra and Imlay, 2012). Because of the essential roles of catalase and AhpR in H2O2-scavenging, bacterial strains lacking both together display a drastically elevated sensitivity to H2O2 and carry an apparent aerobic growth defect (Cosgrove et al, 2007; Ezraty et al, 2017)
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