Flagellated bacteria swim by rotating a bundle of helical flagella and commonly explore the surrounding environment in a “run-and-tumble” motility mode. Here, we show that the upcoming flow could impact the bacterial run-and-tumble behavior by affecting the formation and dispersal of the flagellar bundle. Using a dual optical tweezers setup to trap individual bacteria, we characterized the effects of the imposed fluid flow and cell body rotation on the run-and-tumble behavior. We found that the two factors affect the behavior differently, with the imposed fluid flow increasing the running time and decreasing the tumbling time and the cell body rotation decreasing the tumbling time only. Using numerical simulations, we computed the flagellar bundling time as a function of flow velocity, which agrees well with our experimental observations. The mechanical effects we characterized here provide novel, to our knowledge, ingredients for further studies of bacterial chemotaxis in complex environments such as dynamic fluid environments.

带鞭毛的细菌通过旋转一束螺旋鞭毛来游泳，并且通常以“奔跑”的运动模式探索周围环境。在这里，我们表明即将到来的流动可能通过影响鞭毛束的形成和分散来影响细菌的奔跑和翻滚行为。使用双光镊设置来捕获单个细菌，我们描述了施加的流体流动和细胞体旋转对跑步和翻滚行为的影响。我们发现这两个因素对行为的影响不同，施加的流体流动增加了运行时间并减少了翻滚时间，而细胞体旋转仅减少了翻滚时间。使用数值模拟，我们计算了鞭毛捆绑时间作为流速的函数，这与我们的实验观察结果非常吻合。