Texas A&M University Health Science Center, Bryan, Texas, USA.
Institute of Fundamental Medicine and Biology, Kazan Federal (Volga Region) University, Kazan, Russia.
mBio. 2020 May 5;11(3):e00528-20. doi: 10.1128/mBio.00528-20.
Nontyphoidal salmonellae (NTS) are exposed to reactive oxygen species (ROS) during their residency in the gut. To survive oxidative stress encountered during infection, salmonellae employ several mechanisms. One of these mechanisms involves the multidrug efflux pump MacAB, although the natural substrate of this pump has not been identified. MacAB homologs in pseudomonads secrete products of nonribosomal peptide synthesis (NRPS). In serovar Typhimurium, the siderophore enterobactin is produced by NRPS in response to iron starvation and this molecule can be processed into salmochelin and several linear metabolites. We found that mutants lacking the key NRPS enzyme EntF are sensitive to peroxide mediated killing and cannot detoxify extracellular HO Moreover, EntF and MacAB function in a common pathway to promote survival of during oxidative stress. We further demonstrated that Typhimurium secretes siderophores in iron-rich media when peroxide is present and that these MacAB-secreted metabolites participate in protection of bacteria against HO We showed that secretion of anti-HO molecules is independent of the presence of the known siderophore efflux pumps EntS and IroC, well-described efflux systems involved in secretion of enterobactin and salmochelin. Both salmochelin and enterobactin are dispensable for Typhimurium protection against ROS; however, linear metabolites of enterobactin produced by esterases IroE and Fes are needed for bacterial survival in peroxide-containing media. We determined that linearized enterobactin trimer protects Typhimurium against peroxide-mediated killing in a MacAB-dependent fashion. Thus, we suggest that linearized enterobactin trimer is a natural substrate of MacAB and that its purpose is to detoxify extracellular reactive oxygen species. Nontyphoidal bacteria induce a classic inflammatory diarrhea by eliciting a large influx of neutrophils, producing a robust oxidative burst. Despite substantial progress understanding the benefits to the host of the inflammatory response to , little is known regarding how can simultaneously resist the damaging effects of the oxidative burst. The multidrug efflux pump is important for survival of oxidative stress both and during infection. We describe a new pathway used by Typhimurium to detoxify extracellular reactive oxygen species using a multidrug efflux pump (MacAB) to secrete a linear siderophore, a metabolite of enterobactin. The natural substrates of many multidrug efflux pumps are unknown, and functional roles of the linear metabolites of enterobactin are unknown. We bring two novel discoveries together to highlight an important mechanism used by to survive under the oxidative stress conditions that this organism encounters during the classic inflammatory diarrhea that it also induces.
非伤寒沙门氏菌（NTS）在肠道中定居时会暴露于活性氧（ROS）。为了在感染过程中存活下来，沙门氏菌采用了几种机制。其中一种机制涉及多药外排泵 MacAB，尽管该泵的天然底物尚未确定。假单胞菌中的 MacAB 同源物分泌非核糖体肽合成（NRPS）的产物。在 血清型鼠伤寒沙门氏菌中，铁载体 enterobactin 由 NRPS 产生，以响应缺铁，并且该分子可以被加工成 salmochelin 和几种线性代谢物。我们发现，缺乏关键 NRPS 酶 EntF 的 突变体对过氧化物介导的杀伤敏感，并且不能解毒细胞外 HO。此外，EntF 和 MacAB 在共同途径中起作用，以促进 在氧化应激下的存活。我们进一步证明，当存在过氧化物时， Typhimurium 在富含铁的培养基中分泌铁载体，并且这些 MacAB 分泌的代谢物参与了细菌对 HO 的保护。我们表明，抗 HO 分子的分泌独立于已知铁载体外排泵 EntS 和 IroC 的存在，这些外排系统涉及 enterobactin 和 salmochelin 的分泌。salmochelin 和 enterobactin 对 Typhimurium 抵御 ROS 都不是必需的；然而，酯酶 IroE 和 Fes 产生的 enterobactin 的线性代谢物对于含有过氧化物的培养基中的细菌存活是必需的。我们确定，线性化 enterobactin 三聚体以 MacAB 依赖的方式保护 Typhimurium 免受过氧化物介导的杀伤。因此，我们认为线性化 enterobactin 三聚体是 MacAB 的天然底物，其目的是解毒细胞外的活性氧。非伤寒沙门氏菌通过引发大量中性粒细胞流入，产生强烈的氧化爆发，引起典型的炎症性腹泻。尽管人们在理解宿主对 炎症反应的好处方面取得了很大进展，但对于 如何能够同时抵抗氧化爆发的破坏性影响知之甚少。多药外排泵 对于 感染期间和感染期间的氧化应激生存都很重要。我们描述了 Typhimurium 用来解毒细胞外活性氧的一种新途径，该途径使用多药外排泵（MacAB）分泌线性铁载体，enterobactin 的代谢物。许多多药外排泵的天然底物尚不清楚，并且 enterobactin 的线性代谢物的功能作用尚不清楚。我们将两个新发现结合在一起，强调了 在感染过程中遇到的经典炎症性腹泻诱导的氧化应激条件下生存的一种重要机制。
