Department of Microbial Pathogenesis, Microbial Sciences Institute, Yale University, West Haven, Connecticut, USA.
Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Aichi Prefecture, Japan.
J Bacteriol. 2018 Oct 10;200(21). doi: 10.1128/JB.00387-18. Print 2018 Nov 1.
The bacterial flagellum has evolved as one of the most remarkable nanomachines in nature. It provides swimming and swarming motilities that are often essential for the bacterial life cycle and pathogenesis. Many bacteria such as and species use flagella as an external propeller to move to favorable environments, whereas spirochetes utilize internal periplasmic flagella to drive a serpentine movement of the cell bodies through tissues. Here, we use cryo-electron tomography to visualize the polar sheathed flagellum of with particular focus on a -specific feature, the H-ring. We characterized the H-ring by identifying its two components FlgT and FlgO. We found that the majority of flagella are located within the periplasmic space in the absence of the H-ring, which are different from those of external flagella in wild-type cells. Our results not only indicate the H-ring has a novel function in facilitating the penetration of the outer membrane and the assembly of the external sheathed flagella but also are consistent with the notion that the flagella have evolved to adapt highly diverse needs by receiving or removing accessary genes. Flagellum is the major organelle for motility in many bacterial species. While most bacteria possess external flagella, such as the multiple peritrichous flagella found in and or the single polar sheathed flagellum in spp., spirochetes uniquely assemble periplasmic flagella, which are embedded between their inner and outer membranes. Here, we show for the first time that the external flagella in can be changed as periplasmic flagella by deleting two flagellar genes. The discovery here may provide new insights into the molecular basis underlying assembly, diversity, and evolution of flagella.
细菌鞭毛已经进化成为自然界中最杰出的纳米机器之一。它提供了游泳和群集运动的动力，这对于细菌的生命周期和发病机制通常是必不可少的。许多细菌，如 和 物种，利用鞭毛作为外部螺旋桨来移动到有利的环境，而螺旋体则利用内部周质鞭毛来驱动细胞体通过组织的蛇形运动。在这里，我们使用冷冻电子断层扫描来可视化 的极性鞘鞭毛，特别关注一个 - 特异性特征，即 H 环。我们通过鉴定其两个组件 FlgT 和 FlgO 来表征 H 环。我们发现，大多数鞭毛位于周质空间内，没有 H 环，这与野生型细胞中外部鞭毛的位置不同。我们的结果不仅表明 H 环在促进外膜穿透和外部鞘鞭毛组装方面具有新的功能，而且还与鞭毛通过接收或去除附加基因来适应高度多样化的需求的观点一致。鞭毛是许多细菌物种运动的主要器官。虽然大多数细菌都具有外部鞭毛，例如 在 和 中发现的多个周毛鞭毛或 中的单个极性鞘鞭毛，但螺旋体独特地组装周质鞭毛，这些鞭毛嵌入在它们的内膜和外膜之间。在这里，我们首次表明，通过删除两个鞭毛基因， 中的外部鞭毛可以变成周质鞭毛。这里的发现可能为鞭毛的组装、多样性和进化的分子基础提供新的见解。
