Biozentrum, University of Basel, Basel, Switzerland.
Infect Immun. 2021 Jun 16;89(7):e0057920. doi: 10.1128/IAI.00579-20.
Francisella tularensis causes the deadly zoonotic disease tularemia in humans and is able to infect a broad range of organisms including arthropods, which are thought to play a major role in transmission. However, while mammalian and infection models are widely used to investigate pathogenicity, a detailed characterization of the major virulence factor, a noncanonical type VI secretion system (T6SS), in an arthropod infection model is missing. Here, we use Galleria mellonella larvae to analyze the role of the T6SS and its corresponding effectors in F. tularensis subsp. virulence. We report that G. mellonella larvae killing depends on the functional T6SS and infectious dose. In contrast to other mammalian infection models, even one of the T6SS effectors PdpC, PdpD, or OpiA is sufficient to kill G. mellonella larvae, while sheath recycling by ClpB is dispensable. We further demonstrate that treatment by polyethylene glycol (PEG) activates T6SS in liquid culture and that this is independent of the response regulator PmrA. PEG-activated IglC secretion is dependent on T6SS structural component PdpB but independent of putative effectors PdpC, PdpD, AnmK, OpiB, OpiB, and OpiB. The results of larvae infection and secretion assay suggest that AnmK, a putative T6SS component with unknown function, interferes with OpiA-mediated toxicity but not with general T6SS activity. We establish that the easy-to-use G. mellonella larvae infection model provides new insights into the function of T6SS and pathogenesis of .
弗朗西斯菌会导致人类致命的人畜共患疾病——野兔热，并且能够感染包括节肢动物在内的广泛生物体，这些生物体被认为在传播中起着重要作用。然而，尽管哺乳动物感染模型和感染模型被广泛用于研究致病性，但在节肢动物感染模型中，一种主要的毒力因子——一种非典型的 VI 型分泌系统（T6SS），其详细特征尚未得到描述。在这里，我们使用家蚕幼虫来分析 T6SS 及其相应效应物在弗朗西斯菌亚种中的作用。我们报告说，家蚕幼虫的死亡依赖于功能正常的 T6SS 和感染剂量。与其他哺乳动物感染模型不同，即使是 T6SS 效应物 PdpC、PdpD 或 OpiA 中的一种，也足以杀死家蚕幼虫，而 ClpB 的鞘回收则是可有可无的。我们进一步证明，聚乙二醇（PEG）处理可在液体培养中激活 T6SS，而这与响应调节子 PmrA 无关。PEG 激活的 IglC 分泌依赖于 T6SS 结构成分 PdpB，但不依赖于假定的效应物 PdpC、PdpD、AnmK、OpiB、OpiB 和 OpiB。幼虫感染和分泌试验的结果表明，AnmK 是一种具有未知功能的假定 T6SS 成分，它干扰 OpiA 介导的毒性，但不干扰一般的 T6SS 活性。我们建立了易于使用的家蚕幼虫感染模型，为 T6SS 的功能和的发病机制提供了新的见解。
