Hydrogen peroxide (H2O2, HP) is a universal toxin that organisms deploy to kill competing or invading cells. Bactericidal action of H2O2 presents several questions. First, the lethal H2O2 concentrations in bacterial cultures are 1000x higher than, for example, those calculated for the phagosome. Second, H2O2-alone kills bacteria in cultures either by mode-one, via iron-mediated chromosomal damage, or by mode-two, via unknown targets, but the killing mode in phagosomes is unclear. Third, phagosomal H2O2 toxicity is enhanced by production of nitric oxide (NO), but in vitro studies disagree: some show NO synergy with H2O2 antimicrobial action, others instead report alleviation. To investigate this "NO paradox," we treated Escherichia coli with various concentrations of H2O2-alone or H2O2+NO, measuring survival and chromosome stability. We found that all NO concentrations make sublethal H2O2 treatments highly lethal, via triggering catastrophic chromosome fragmentation (mode-one killing). Yet, NO-alone is not lethal, potentiating H2O2 toxicity by blocking H2O2 scavenging in cultures. Catalases represent obvious targets of NO inhibition, and catalase-deficient mutants are indeed killed equally by H2O2-alone or H2O2+NO treatments, also showing similar levels of chromosome fragmentation. Interestingly, iron chelation blocks chromosome fragmentation in catalase-deficient mutants without blocking H2O2-alone lethality, indicating mode-two killing. In fact, mode-two killing of WT cells by much higher H2O2 concentrations is transiently alleviated by NO, reproducing the "NO paradox." We conclude that NO potentiates H2O2 toxicity by promoting mode-one killing (via catastrophic chromosome fragmentation) by otherwise static low H2O2 concentrations, while transiently suppressing mode-two killing by immediately lethal high H2O2 concentrations.

中文翻译：

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一氧化氮对过氧化氢酶的抑制作用会增强过氧化氢，从而在大肠杆菌中引发灾难性的染色体断裂。

过氧化氢 (H2O2, HP) 是一种通用毒素，生物体部署它来杀死竞争或入侵的细胞。H2O2 的杀菌作用提出了几个问题。首先，细菌培养物中的致死 H2O2 浓度比例如为吞噬体计算的浓度高 1000 倍。其次，H2O2 单独通过模式一（通过铁介导的染色体损伤）或模式二（通过未知靶标）杀死培养物中的细菌，但吞噬体中的杀死模式尚不清楚。第三，吞噬体 H2O2 的毒性因一氧化氮 (NO) 的产生而增强，但体外研究不同意：一些研究显示 NO 与 H2O2 的抗菌作用有协同作用，而另一些则报告了缓解作用。为了研究这种“NO 悖论”，我们用不同浓度的 H2O2 单独或 H2O2+NO 处理大肠杆菌，测量存活率和染色体稳定性。我们发现，所有 NO 浓度都会通过触发灾难性的染色体碎片（模式一杀戮）使亚致死性 H2O2 治疗高度致命。然而，NO 本身并不是致命的，它通过阻止培养物中的 H2O2 清除来增强 H2O2 的毒性。过氧化氢酶代表 NO 抑制的明显目标，过氧化氢酶缺陷突变体确实被 H2O2 单独或 H2O2+NO 处理同样杀死，也显示出相似水平的染色体片段化。有趣的是，铁螯合可阻断过氧化氢酶缺陷突变体中的染色体断裂，而不会阻断 H2O2 单独的致死性，表明模式二杀伤。事实上，通过更高浓度的 H2O2 杀死 WT 细胞的模式二会被 NO 暂时缓解，从而重现“NO 悖论”。