论文标题
在细菌鞭毛的束形成期间，直接与间接流体动力相互作用
Direct vs indirect hydrodynamic interactions during bundle formation of bacterial flagella
论文作者
论文摘要
大多数运动细菌通过旋转多个螺旋鞭毛细丝在粘性液中游泳。这些半刚性丝反复连接（“束”）和分开（“无缠绕”），从而导致了单元的两对准随机行动运动。在此过程中，已知细丝之间的流体动力相互作用起着重要作用，可以分为两种不同的类型：通过通过丝素本身的致动而产生的流程介导的直接相互作用，以及通过细胞体运动介导的间接相互作用（即，在促进前进的游泳框架中诱导的流动型）。为了了解这两种相互作用的相对重要性，我们研究了鞭毛捆绑的最小奇点模型。使用流体动力图像，我们通过分析求解流量，并准确地计算直接和间接相互作用，这是鞭毛丝的长度及其角度分离的函数。我们表明（i）仅鞭毛的产生就足以通过两种类型的相互作用将系统驱动到捆绑状态； （ii）间接对流在长细丝和大分离中主导，即主要在捆绑过程的早期阶段； （iii）相比之下，当鞭毛细丝在彼此的尾流中时，直接相互作用占主导地位，我们从数学上表征了这一点。我们进一步引入了一个数值弹性水力动力学模型，该模型使我们能够分别分析直接和间接相互作用，计算每个鞭毛细丝的螺旋轴的动力学。因此，我们表明（IV）在捆绑过程中直接和间接相互作用之间的平衡转移是非单调的，并且直接优势的峰值，并且鞭毛的不同部分受这些变化对不同扩展的影响。
Most motile bacteria swim in viscous fluids by rotating multiple helical flagellar filaments. These semi-rigid filaments repeatedly join ('bundle') and separate ('unbundle'), resulting in a two-gait random walk-like motion of the cell. In this process, hydrodynamic interactions between the filaments are known to play an important role and can be categorised into two distinct types: direct interactions mediated through flows that are generated through the actuation of the filaments themselves, and indirect interactions mediated through the motion of the cell body (i.e. flows induced in the swimming frame that result from propulsion). To understand the relative importance of these two types of interactions, we study a minimal singularity model of flagellar bundling. Using hydrodynamic images, we solve for the flow analytically and compute both direct and indirect interactions exactly as a function of the length of the flagellar filaments and their angular separation. We show (i) that the generation of thrust by flagella alone is sufficient to drive the system towards a bundled state through both types of interaction; (ii) that indirect advection dominates for long filaments and at wide separation, i.e. primarily during the early stages of the bundling process; and (iii) that, in contrast, direct interactions dominate when flagellar filaments are in each other's wake, which we characterise mathematically. We further introduce a numerical elastohydrodynamic model that allows us to compute the dynamics of the helical axes of each flagellar filament while analysing direct and indirect interactions separately. With this we show (iv) that the shift in balance between direct and indirect interactions is non-monotonic during the bundling process, with a peak in direct dominance, and that different sections of the flagella are affected by these changes to different extents.
