Deng Jiayi, Molaei Mehdi, Chisholm Nicholas G, Stebe Kathleen J
Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, United States.
Langmuir. 2020 Jun 30;36(25):6888-6902. doi: 10.1021/acs.langmuir.9b03578. Epub 2020 Mar 4.
Bacteria are important examples of active or self-propelled colloids. Because of their directed motion, they accumulate near interfaces. There, they can become trapped and swim adjacent to the interface via hydrodynamic interactions, or they can adsorb directly and swim in an adhered state with complex trajectories that differ from those in bulk in both form and spatiotemporal implications. We have adopted the monotrichous bacterium PA01 as a model species and have studied its motion at oil-aqueous interfaces. We have identified conditions in which bacteria swim persistently without restructuring the interface, allowing detailed and prolonged study of their motion. In addition to characterizing the ensemble behavior of the bacteria, we have observed a gallery of distinct trajectories of individual swimmers on and near fluid interfaces. We attribute these diverse swimming behaviors to differing trapped states for the bacteria in the fluid interface. These trajectory types include Brownian diffusive paths for passive adsorbed bacteria, curvilinear trajectories including curly paths with radii of curvature larger than the cell body length, and rapid pirouette motions with radii of curvature comparable to the cell body length. Finally, we see interfacial visitors that come and go from the interfacial plane. We characterize these individual swimmer motions. This work may impact nutrient cycles for bacteria on or near interfaces in nature. This work will also have implications in microrobotics, as active colloids in general and bacteria in particular are used to carry cargo in this burgeoning field. Finally, these results have implications in engineering of active surfaces that exploit interfacially trapped self-propelled colloids.
细菌是主动或自驱动胶体的重要例子。由于它们的定向运动，它们会在界面附近聚集。在那里，它们可能会被困住，并通过流体动力相互作用在界面附近游动，或者它们可以直接吸附，并以附着状态游动，其复杂轨迹在形式和时空影响方面都与在本体中的轨迹不同。我们采用单端鞭毛菌PA01作为模型物种，并研究了它在油水界面的运动。我们确定了细菌在不改变界面结构的情况下持续游动的条件，从而能够对其运动进行详细和长时间的研究。除了表征细菌的整体行为外，我们还观察到了单个游动者在流体界面上及其附近的一系列不同轨迹。我们将这些多样的游动行为归因于细菌在流体界面中处于不同的被困状态。这些轨迹类型包括被动吸附细菌的布朗扩散路径、曲率半径大于细胞体长的曲线轨迹，如卷曲路径，以及曲率半径与细胞体长相当的快速旋转运动。最后，我们看到有界面访客在界面平面上来去。我们对这些单个游动者的运动进行了表征。这项工作可能会影响自然界中界面上或其附近细菌的营养循环。这项工作在微型机器人技术方面也将具有重要意义，因为一般的活性胶体，特别是细菌，在这个新兴领域被用于运载货物。最后，这些结果对利用界面捕获的自驱动胶体的活性表面工程具有重要意义。
