Chen Meiting, Zhao Ziyi, Yang Jin, Peng Kai, Baker Matthew Ab, Bai Fan, Lo Chien-Jung
Department of Physics and Graduate Institute of Biophysics, National Central University, Jhongli, Taiwan.
Biodynamic Optical Imaging Center (BIOPIC), School of Life Sciences, Peking University, Beijing, China.
Elife. 2017 Jan 18;6:e22140. doi: 10.7554/eLife.22140.
Bacterial flagella are extracellular filaments that drive swimming in bacteria. During motor assembly, flagellins are transported unfolded through the central channel in the flagellum to the growing tip. Here, we applied in vivo fluorescent imaging to monitor in real time the polar flagella growth. The flagellar growth rate is found to be highly length-dependent. Initially, the flagellum grows at a constant rate (50 nm/min) when shorter than 1500 nm. The growth rate decays sharply when the flagellum grows longer, which decreases to ~9 nm/min at 7500 nm. We modeled flagellin transport inside the channel as a one-dimensional diffusive process with an injection force at its base. When the flagellum is short, its growth rate is determined by the loading speed at the base. Only when the flagellum grows longer does diffusion of flagellin become the rate-limiting step, dramatically reducing the growth rate. Our results shed new light on the dynamic building process of this complex extracellular structure.
细菌鞭毛是驱动细菌游动的细胞外细丝。在鞭毛组装过程中，鞭毛蛋白以未折叠状态通过鞭毛中的中央通道运输到生长顶端。在此，我们应用体内荧光成像技术实时监测极鞭毛的生长。发现鞭毛的生长速率高度依赖于长度。最初，当鞭毛短于1500纳米时，它以恒定速率（50纳米/分钟）生长。当鞭毛变长时，生长速率急剧下降，在7500纳米时降至约9纳米/分钟。我们将通道内鞭毛蛋白的运输建模为一维扩散过程，在其基部有一个注入力。当鞭毛短时，其生长速率由基部的加载速度决定。只有当鞭毛变长时，鞭毛蛋白的扩散才成为限速步骤，显著降低生长速率。我们的结果为这种复杂细胞外结构的动态构建过程提供了新的见解。
