Mechanical properties of bacterial hook filament

像Sal这样的鞭毛细菌。鼠伤寒蚤通过旋转螺旋鞭毛细丝来游泳，鞭毛细丝相互捆绑并同步。由于细菌马达的轴向不同，马达与鞭毛丝之间需要有柔性连接部分。已知细菌钩作为该零件的万向节工作。然而，其刚性等力学特性尚不清楚。本文采用突变体Sal的长约1μm的多钩长丝对其刚性模量进行了测量。沙门氏菌感染(SWJ108)。纯化的多钩鱼丝在液态乙烷中快速冷冻并冷冻干燥。利用电子显微镜的阴影图像对螺旋螺距和直径的分布进行了评价。结果表明，多钩丝的螺旋螺距为95±23nm，直径为31±9.9nm。我们还测量了阴性染色样品的螺旋节距和鞭毛丝直径的波动。通过比较多钩和鞭毛丝的波动，我们计算出刚性比为G_<鞭毛>/G<钩>=120。根据鞭毛丝刚度的文献值3.8×10^9Pa，得到多钩的刚度为3.3×10^7Pa。我们还尝试用薄玻璃毛细管直接测量鞭毛在溶液中的刚性。用直径小于1μm的玻璃毛细管吸附抗鞭毛蛋白固定荧光标记的鞭毛丝。在荧光显微镜下通过玻璃毛细管的弯曲变形测量pN范围内的张力。我们现在正在积累这一过程的成果。我们将用同样的方法测量长度为几微米的超聚钩的刚度。

Flagellated bacteria like Sal. Typhimurium swims by rotating helical flagella filaments with bundling and synchronizing them each other. Because axs of bacterial motors directed in different way, flexible joint part is required between motor and flagella filament. It is known that bacterial hook work as a universal joint of this part. However its mechanical feature like rigidity is not known exactly. Here we measured modulus of rigidity by using polyhook filament, length about 1μm, from mutant Sal. Typhimurium(SWJ108). Purified polyhook filaments were frozen rapidly in liquid ethane and freeze dried. Distribution of helix pitch and diameter were evaluated from electron micrographs of shadowed images. We got value of 95±23nm for helix pitch and 31±9.9nm for diameter of polyhook filament. We also measured fluctuation of helical pitch and diameter of flagella filament from negative stained samples. By comparing fluctuation of polyhook and flagella filaments, we have calculated the ratio of rigidity as G_<flagella>/G<hook>=120. According to the literature value of flagella filament rigidity, 3.8×10^9Pa, we obtained rigidity of polyhook as 3.3×10^7Pa. We also tried to measure the rigidity of flagella in solution directly using thin glass capillary. Fluorescent labeled flagella filament was fixed by anti-flagellin adsorbed on a glass capillary of diameter less than 1μm. Tension in pN range was measured from bending deformation of glass capillary under fluorescent microscope. We are now accumulating the results in this process. We are going to measure rigidity of super-poly hook which has length of few micro-meter by the same method.