Iron Triggers λSo Prophage Induction and Release of Extracellular DNA in Shewanella oneidensis MR-1 Biofilms
Iron Triggers λSo Prophage Induction and Release of Extracellular DNA in Shewanella oneidensis MR-1 Biofilms
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DOI：
10.1128/aem.01480-14
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发表时间：
2014-09-01
影响因子：
4.4
通讯作者：
Thormann, Kai M.
中科院分区：
文献类型：
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作者：
Binnenkade, Lucas;Teichmann, Laura;Thormann, Kai M.
原噬菌体是细菌染色体中普遍存在的元件，并以多种方式影响宿主的生理学和生态学。我们之前已经证明，希瓦氏菌 MR-1 中细胞外 DNA (eDNA) 释放和正常生物膜形成需要噬菌体诱导的裂解。在这里，我们研究了生物膜中前噬菌体 lambda So 时空诱导的调节机制。为此，我们使用功能性荧光融合来监测各种突变背景下的 lambda So 激活以及对不同生理条件的反应。 lambda So 诱导主要以严格 RecA 依赖性方式发生在丝状细胞亚群中，表明氧化应激诱导的 DNA 损伤是主要触发因素。因此，受到氧化应激反应（Delta oxyR）或铁稳态（Delta Fur）影响的突变体表现出噬菌体诱导水平急剧增加和异常生物膜形成，而浮游细胞则没有或仅受到轻微影响。为了进一步研究氧化应激的作用，我们进行了突变体筛选，并鉴定了 OxyR 中两个独立的氨基酸取代（T104N 和 L197P），它们抑制过氧化氢 (H2O2) 诱导 lambda So。然而，两种突变体形成的生物膜中的 lambda So 诱导并未受到抑制，表明细胞内 H2O2 在此过程中的作用较小。相比之下，向生物膜中添加铁强烈增强了 lambda So 诱导和 eDNA 释放，而这两个过程在低铁水平下均受到显着抑制，强烈表明铁是限制因素。我们得出的结论是，生物膜形成过程中铁的吸收触发了 lambda So 介导的细胞亚群裂解，这可能是通过 RecA 感知到的铁介导的 DNA 损伤的增加所致。
Prophages are ubiquitous elements within bacterial chromosomes and affect host physiology and ecology in multiple ways. We have previously demonstrated that phage-induced lysis is required for extracellular DNA (eDNA) release and normal biofilm formation in Shewanella oneidensis MR-1. Here, we investigated the regulatory mechanisms of prophage lambda So spatiotemporal induction in biofilms. To this end, we used a functional fluorescence fusion to monitor lambda So activation in various mutant backgrounds and in response to different physiological conditions. lambda So induction occurred mainly in a subpopulation of filamentous cells in a strictly RecA-dependent manner, implicating oxidative stress-induced DNA damage as the major trigger. Accordingly, mutants affected in the oxidative stress response (Delta oxyR) or iron homeostasis (Delta fur) displayed drastically increased levels of phage induction and abnormal biofilm formation, while planktonic cells were not or only marginally affected. To further investigate the role of oxidative stress, we performed a mutant screen and identified two independent amino acid substitutions in OxyR (T104N and L197P) that suppress induction of lambda So by hydrogen peroxide (H2O2). However, lambda So induction was not suppressed in biofilms formed by both mutants, suggesting a minor role of intracellular H2O2 in this process. In contrast, addition of iron to biofilms strongly enhanced lambda So induction and eDNA release, while both processes were significantly suppressed at low iron levels, strongly indicating that iron is the limiting factor. We conclude that uptake of iron during biofilm formation triggers lambda So-mediated lysis of a subpopulation of cells, likely by an increase in iron-mediated DNA damage sensed by RecA.