Manganese scavenging and oxidative stress response mediated by type VI secretion system in Burkholderia thailandensis
Manganese scavenging and oxidative stress response mediated by type VI secretion system in Burkholderia thailandensis
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泰国伯克霍尔德菌 VI 型分泌系统介导的锰清除和氧化应激反应
DOI：
10.1073/pnas.1614902114
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发表时间：
2017-03-14
影响因子：
11.1
通讯作者：
Shen, Xihui
中科院分区：
文献类型：
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作者：
Si, Meiru;Zhao, Chao;Shen, Xihui
作为一种必需的微量营养素，革兰氏阴性菌必须通过主动转运系统将Mn 2+浓缩到细胞溶质中以满足细胞的需求。尽管已经表征了内膜Mn 2+转运蛋白，但是尚未描述用于Mn 2+跨外膜转运的活性转运蛋白。在这里，我们报告了一个Mn 2 +-清除途径组成的一个新发现的TonB依赖的外膜锰转运蛋白，MnoT，和VI型分泌系统（T6 SS）分泌的Mn 2 +-结合蛋白，TseM。传统上，T6 SS被认为是一种接触依赖性的纳米机器，可以将效应物注入真核或原核细胞中，以获得毒力或细菌间竞争。本文报道的T6 SS在金属获取和细菌-细菌竞争中的非接触性功能表明，T6 SS可能已被某些细菌改造，以在进化过程中获得额外的适应功能。VI型分泌系统（T6 SS）是一种广泛存在于革兰氏阴性菌中的多功能蛋白质输出系统。已知T6 SS将蛋白质底物转运至真核和原核靶细胞以引起细胞损伤，T6 SS主要被认为是微生物-宿主和微生物种间竞争的接触依赖性细菌武器。在这里，我们报告的接触无关的功能T6 SS的金属收购，细菌竞争，抗氧化应激。我们表明，T6 SS-4在伯克霍尔德氏菌泰国是至关重要的生存氧化应激下，受OxyR，一个保守的氧化应激调节。T6 SS-4对氧化应激下细胞内锰（Mn 2+）的积累很重要。接下来，我们鉴定了T6 SS-4依赖性Mn 2+结合效应子TseM及其相互作用伴侣MnoT，Mn 2+特异性TonB依赖性外膜转运蛋白。与T6 SS-4基因类似，mnoT的表达受OxyR调节，并在氧化应激和低Mn 2+条件下诱导。TseM和MnoT都是在Mn 2+限制和氧化应激条件下跨外膜有效吸收Mn 2+所必需的。TseM-MnoT介导的主动Mn 2+转运系统也参与非接触性细菌-细菌竞争和细菌毒力。这一发现为理解金属离子摄取机制和T6 SS在细菌-细菌竞争中的作用提供了一个视角。
Significance As an essential micronutrient, Gram-negative bacteria must concentrate Mn2+ into the cytosol via active transport systems to meet cellular demands. Whereas inner membrane Mn2+ transporters have been characterized, an active transporter for translocation of Mn2+ across the outer membrane has not been described. Here we report a Mn2+-scavenging pathway consisting of a newly identified TonB-dependent outer membrane manganese transporter, MnoT, and a type VI secretion system (T6SS)-secreted Mn2+-binding protein, TseM. Traditionally, T6SS is recognized as a contact-dependent nanomachine to inject effectors into eukaryotic or prokaryotic cells for virulence or for interbacterial competition. The contact-independent functions of T6SS for metal acquisition and bacteria–bacteria competition, reported here, suggest that T6SS may have been retrofitted by some bacteria to gain additional adaptive functions during evolution. Type VI secretion system (T6SS) is a versatile protein export machinery widely distributed in Gram-negative bacteria. Known to translocate protein substrates to eukaryotic and prokaryotic target cells to cause cellular damage, the T6SS has been primarily recognized as a contact-dependent bacterial weapon for microbe–host and microbial interspecies competition. Here we report contact-independent functions of the T6SS for metal acquisition, bacteria competition, and resistance to oxidative stress. We demonstrate that the T6SS-4 in Burkholderia thailandensis is critical for survival under oxidative stress and is regulated by OxyR, a conserved oxidative stress regulator. The T6SS-4 is important for intracellular accumulation of manganese (Mn2+) under oxidative stress. Next, we identified a T6SS-4–dependent Mn2+-binding effector TseM, and its interacting partner MnoT, a Mn2+-specific TonB-dependent outer membrane transporter. Similar to the T6SS-4 genes, expression of mnoT is regulated by OxyR and is induced under oxidative stress and low Mn2+ conditions. Both TseM and MnoT are required for efficient uptake of Mn2+ across the outer membrane under Mn2+-limited and -oxidative stress conditions. The TseM–MnoT-mediated active Mn2+ transport system is also involved in contact-independent bacteria–bacteria competition and bacterial virulence. This finding provides a perspective for understanding the mechanisms of metal ion uptake and the roles of T6SS in bacteria–bacteria competition.