Peng Yi, Liu Zhengyang, Cheng Xiang
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Sci Adv. 2021 Apr 23;7(17). doi: 10.1126/sciadv.abd1240. Print 2021 Apr.
We experimentally study the emergence of collective bacterial swimming, a phenomenon often referred to as bacterial turbulence. A phase diagram of the flow of 3D suspensions spanned by bacterial concentration, the swimming speed of bacteria, and the number fraction of active swimmers is systematically mapped, which shows quantitative agreement with kinetic theories and demonstrates the dominant role of hydrodynamic interactions in bacterial collective swimming. We trigger bacterial turbulence by suddenly increasing the swimming speed of light-powered bacteria and image the transition to the turbulence in real time. Our experiments identify two unusual kinetic pathways, i.e., the one-step transition with long incubation periods near the phase boundary and the two-step transition driven by long-wavelength instabilities deep inside the turbulent phase. Our study provides not only a quantitative verification of existing theories but also insights into interparticle interactions and transition kinetics of bacterial turbulence.
我们通过实验研究了集体细菌游动的出现，这一现象常被称为细菌湍流。系统地绘制了由细菌浓度、细菌游动速度和活跃游动者的数量分数所构成的三维悬浮液流动相图，该相图与动力学理论显示出定量一致性，并证明了流体动力学相互作用在细菌集体游动中的主导作用。我们通过突然提高光驱动细菌的游动速度来引发细菌湍流，并实时成像向湍流的转变。我们的实验确定了两条不同寻常的动力学路径，即在相边界附近具有长潜伏期的一步转变以及在湍流相深处由长波长不稳定性驱动的两步转变。我们的研究不仅对现有理论进行了定量验证，还深入了解了细菌湍流中的粒子间相互作用和转变动力学。
