游过粘性流体,鞭毛细菌必须通过旋转鞭毛或一束多个鞭毛来克服其身体上的液体阻力。因为阻力随着细菌的大小而增加,从理论上讲,细菌的游泳速度与其体长成反比。然而,尽管进行了广泛的研究,鞭毛细菌的基本大小-速度关系尚不清楚,不同实验报告的结果相互矛盾.这里,通过批判性地审查现有的证据并协同我们自己的大样本量实验,流体动力学建模,和模拟,我们证明了大肠杆菌的平均游泳速度,一个主要的细菌模型,与它们的身体长度无关。我们的定量分析表明,这种违反直觉的关系是由体长与细菌鞭毛数量之间的线性相关所决定的集体鞭毛动力学的结果。值得注意的是,我们的研究揭示了细菌如何利用越来越多的鞭毛来调节鞭毛的运动负荷。多个鞭毛之间的集体负载共享导致每个鞭毛马达上的负载较低,因此鞭毛旋转更快,这补偿了较高的液体对较长的细菌体的阻力。如果没有这种平衡机制,单调细菌的游泳速度通常随着体长的增加而降低,限制细菌大小变化的特征。总之,我们的研究解决了长期以来关于鞭毛细菌大小-速度关系的争议,并提供了对细菌中多鞭毛的功能益处的见解.
To swim through a viscous fluid, a flagellated bacterium must overcome the fluid drag on its body by rotating a flagellum or a bundle of multiple flagella. Because the drag increases with the size of bacteria, it is expected theoretically that the swimming speed of a bacterium inversely correlates with its body length. Nevertheless, despite extensive research, the fundamental size-speed relation of flagellated bacteria remains unclear with different experiments reporting conflicting results. Here, by critically reviewing the existing evidence and synergizing our own experiments of large sample sizes, hydrodynamic modeling, and simulations, we demonstrate that the average swimming speed of Escherichia coli, a premier model of peritrichous bacteria, is independent of their body length. Our quantitative analysis shows that such a counterintuitive relation is the consequence of the collective flagellar dynamics dictated by the linear correlation between the body length and the number of flagella of bacteria. Notably, our study reveals how bacteria utilize the increasing number of flagella to regulate the flagellar motor load. The collective load sharing among multiple flagella results in a lower load on each flagellar motor and therefore faster flagellar rotation, which compensates for the higher fluid drag on the longer bodies of bacteria. Without this balancing mechanism, the swimming speed of monotrichous bacteria generically decreases with increasing body length, a feature limiting the size variation of the bacteria. Altogether, our study resolves a long-standing controversy over the size-speed relation of flagellated bacteria and provides insights into the functional benefit of multiflagellarity in bacteria.