Vibrio species are Gram-negative rod-shaped bacteria that are ubiquitous and often highly motile in aqueous environments. Vibrio swimming motility is driven by a polar flagellum covered with a membranous sheath, but this sheathed flagellum is not well understood at the molecular level because of limited structural information. Here, we use Vibrio alginolyticus as a model system to study the sheathed flagellum in intact cells by combining cryoelectron tomography (cryo-ET) and subtomogram analysis with a genetic approach. We reveal striking differences between sheathed and unsheathed flagella in V. alginolyticus cells, including a novel ring-like structure at the bottom of the hook that is associated with major remodeling of the outer membrane and sheath formation. Using mutants defective in flagellar motor components, we defined a Vibrio-specific feature (also known as the T ring) as a distinctive periplasmic structure with 13-fold symmetry. The unique architecture of the T ring provides a static platform to recruit the PomA/B complexes, which are required to generate higher torques for rotation of the sheathed flagellum and fast motility of Vibrio cells. Furthermore, the Vibrio flagellar motor exhibits an intrinsic length variation between the inner and the outer membrane bound complexes, suggesting the outer membrane bound complex can shift slightly along the axial rod during flagellar rotation. Together, our detailed analyses of the polar flagella in intact cells provide insights into unique aspects of the sheathed flagellum and the distinct motility of Vibrio species.

中文翻译：

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溶藻弧菌的鞘极鞭毛的分子结构

弧菌是革兰氏阴性杆状细菌，在水环境中普遍存在，并且通常具有很高的运动力。弧菌游泳运动是由覆盖有膜鞘的极鞭毛驱动的，但是由于有限的结构信息，这种鞘鞘的鞭毛在分子水平上还没有被很好地理解。在这里，我们使用溶藻弧菌作为模型系统，通过将冷冻电子断层扫描（cryo-ET）和断层图像分析与遗传方法相结合，研究完整细胞中带鞘的鞭毛。我们揭示溶藻弧菌的鞘和未鞘鞭毛之间的显着差异细胞，在钩的底部包括一种新颖的环状结构，与外膜的重大重塑和鞘的形成有关。使用鞭毛运动成分缺陷的突变体，我们将弧菌特异性特征（也称为T环）定义为具有13倍对称性的独特周质结构。T环的独特结构为招募PomA / B复合物提供了一个静态平台，这需要产生更高的扭矩来旋转鞘膜鞭毛和弧菌细胞的快速运动。此外，弧菌鞭毛马达在内部和外部膜结合复合物之间表现出固有的长度变化，这表明在鞭毛旋转期间，外部膜结合复合物可沿轴向杆轻微移动。总之，我们对完整细胞中极鞭毛的详细分析提供了对鞘式鞭毛的独特方面以及弧菌物种独特运动性的见解。