Pathogenesis of Vascular Infections Unit, Institut Pasteur, 75015, Paris, France.
Service de Physique de l'Etat Condensé, CEA, CNRS, Université Paris-Saclay, CEA-Saclay, 91191, Gif-sur-Yvette, France.
Nat Commun. 2018 Oct 26;9(1):4486. doi: 10.1038/s41467-018-06842-6.
A suspension of swimming bacteria is possibly the simplest realization of active matter, i.e. a class of systems transducing stored energy into mechanical motion. Collective swimming of hydrodynamically interacting bacteria resembles turbulent flow. This seemingly chaotic motion can be rectified by a geometrical confinement. Here we report on self-organization of a concentrated suspension of motile bacteria Bacillus subtilis constrained by two-dimensional (2D) periodic arrays of microscopic vertical pillars. We show that bacteria self-organize into a lattice of hydrodynamically bound vortices with a long-range antiferromagnetic order controlled by the pillars' spacing. The patterns attain their highest stability and nearly perfect order for the pillar spacing comparable with an intrinsic vortex size of an unconstrained bacterial turbulence. We demonstrate that the emergent antiferromagnetic order can be further manipulated and turned into a ferromagnetic state by introducing chiral pillars. This strategy can be used to control a wide class of active 2D systems.
悬浮游动的细菌可能是最简单的活性物质实现形式，即一类将储存的能量转化为机械运动的系统。受水力作用影响而集体游动的细菌类似于湍流。这种看似混乱的运动可以通过几何约束来纠正。在这里，我们报告了受二维（2D）周期性微垂直立柱阵列约束的运动细菌枯草芽孢杆菌浓缩悬浮液的自组织现象。我们表明，细菌会自组织成一个由水力束缚的漩涡组成的晶格，其具有由立柱间距控制的长程反铁磁序。对于与无约束细菌湍流的固有涡旋大小相当的立柱间距，图案达到了最高的稳定性和近乎完美的有序性。我们证明，通过引入手性立柱，可以进一步操纵并将新出现的反铁磁序转变为铁磁态。这种策略可用于控制广泛的二维活性系统。
