Peritrichous bacteria synchronize and bundle their flagella to actively swim, while disruption of the bundle leads to a slow motility phase with a weak propulsion. It is still not known whether the number of flagella represents an evolutionary adaptation toward optimizing bacterial navigation. We study the swimming dynamics of differentially flagellated Bacillus subtilis strains in a quasi-two-dimensional system. We find that decreasing the number of flagella N_f reduces the average turning angle between two successive run phases and enhances the run time and the directional persistence of the run phase. As a result, having fewer flagella is beneficial for long-distance transport and fast spreading, while having a lot of flagella is advantageous for the processes that require a slower spreading, such as biofilm formation. We develop a two-state random walk model that incorporates spontaneous switchings between the states and yields exact analytical expressions for transport properties, in remarkable agreement with experiments. The results of numerical simulations based on our two-state model suggest that the efficiency of searching and exploring the environment is optimized at intermediate values of N_f. The optimal choice of N_f, for which the search time is minimized, decreases with increasing the size of the environment in which the bacteria swim.

中文翻译：

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鞭毛数量决定细菌的传播和运输效率。

周毛细菌同步并捆绑其鞭毛以主动游动，而鞭毛束的破坏会导致推进力较弱的缓慢运动阶段。目前尚不清楚鞭毛的数量是否代表了优化细菌导航的进化适应。我们研究了准二维系统中差异鞭毛枯草芽孢杆菌菌株的游动动力学。我们发现，减少鞭毛数量N _f会减少两个连续运行阶段之间的平均转动角度，并提高运行时间和运行阶段的方向持久性。因此，较少的鞭毛有利于长距离运输和快速扩散，而较多的鞭毛有利于需要较慢扩散的过程，例如生物膜形成。我们开发了一种二态随机游走模型，该模型结合了状态之间的自发切换，并产生输运特性的精确解析表达式，与实验非常一致。基于我们的两种状态模型的数值模拟结果表明，搜索和探索环境的效率在N _f的中间值处得到优化。N _f的最佳选择（搜索时间最小化）随着细菌游动环境大小的增加而减小。