Bacteria solve the problem of crowding by moving slowly
Bacteria solve the problem of crowding by moving slowly
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DOI：
10.1038/s41567-020-01070-6
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发表时间：
2020-11-23
期刊：
影响因子：
19.6
通讯作者：
Durham, W. M.
中科院分区：
文献类型：
--
作者：
Meacock, O. J.;Doostmohammadi, A.;Durham, W. M.
细菌通常以包含数十亿个细胞的密集集合体附着在表面上(1)。虽然众所周知，运动性使这些群体能够集体扩张到新的领域(2-5)，但细菌如何在如此紧密的条件下集体穿过表面仍知之甚少。在这里，我们结合实验、细胞追踪和基于个体的建模来研究病原体铜绿假单胞菌，因为它使用抓钩状菌毛集体在表面迁移(3,6,7)。我们发现，在高细胞密度下，超毛化突变体的快速移动细胞会被移动较慢的野生型细胞超越并击败。利用研究液晶的理论(8-13)，我们证明这种效应是由拓扑缺陷的物理现象介导的，拓扑缺陷是具有不同方向的细胞彼此相遇的点。我们的分析表明，当拓扑电荷 +1/2 的缺陷相互碰撞时，快速移动的突变细胞会旋转到垂直方向并被捕获。通过更慢地移动，野生型细胞避免了这种捕获机制并产生集体行为，从而导致更快的迁移。通过这种方式，液晶物理学解释了缓慢的细菌如何在争夺新领地的竞争中击败更快的细胞。细菌能够作为巨大而密集的集体移动。作者在这里表明，缓慢的运动是这种集体行为的关键，因为速度更快的细菌会导致拓扑缺陷碰撞在一起并将细胞困在适当的位置。
Bacteria commonly live attached to surfaces in dense collectives containing billions of cells(1). While it is known that motility allows these groups to expand en masse into new territory(2-5), how bacteria collectively move across surfaces under such tightly packed conditions remains poorly understood. Here we combine experiments, cell tracking and individual-based modelling to study the pathogen Pseudomonas aeruginosa as it collectively migrates across surfaces using grappling-hook-like pili(3,6,7). We show that the fast-moving cells of a hyperpilated mutant are overtaken and outcompeted by the slower-moving wild type at high cell densities. Using theory developed to study liquid crystals(8-13), we demonstrate that this effect is mediated by the physics of topological defects, points where cells with different orientations meet one another. Our analyses reveal that when defects with topological charge +1/2 collide with one another, the fast-moving mutant cells rotate to point vertically and become trapped. By moving more slowly, wild-type cells avoid this trapping mechanism and generate collective behaviour that results in faster migration. In this way, the physics of liquid crystals explains how slow bacteria can outcompete faster cells in the race for new territory.Bacteria are able to move as vast, dense collectives. Here the authors show that slow movement is key to this collective behaviour because faster bacteria cause topological defects to collide together and trap cells in place.