Copenhagen Katherine, Alert Ricard, Wingreen Ned S, Shaevitz Joshua W
Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA.
Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544, USA.
Nat Phys. 2021 Feb;17(2):211-215. doi: 10.1038/s41567-020-01056-4. Epub 2020 Nov 23.
The soil bacterium lives in densely packed groups that form dynamic three-dimensional patterns in response to environmental changes, such as droplet-like fruiting bodies during starvation. The development of these multicellular structures begins with the sequential formation of cell layers in a process that is poorly understood. Using confocal three-dimensional imaging, we find that motile rod-shaped cells are densely packed and aligned in each layer, forming an active nematic liquid crystal. Cell alignment is nearly perfect throughout the population except at point defects that carry half-integer topological charge. We observe that new cell layers preferentially form at the position of +1/2 defects, whereas holes preferentially open at -1/2 defects. To explain these findings, we model the bacterial colony as an extensile active nematic fluid with anisotropic friction. In agreement with our experimental measurements, this model predicts an influx of cells toward +1/2 defects, and an outflux of cells from -1/2 defects. Our results suggest that cell motility and mechanical cell-cell interactions are sufficient to promote the formation of cell layers at topological defects, thereby seeding fruiting bodies in colonies of .
这种土壤细菌以密集排列的群体形式存在，会根据环境变化形成动态的三维模式，比如在饥饿时形成水滴状的子实体。这些多细胞结构的发育始于细胞层的顺序形成，而这一过程目前还了解甚少。利用共聚焦三维成像技术，我们发现活动的杆状细胞在每一层中都紧密排列且相互对齐，形成一种活性向列型液晶。除了携带半整数拓扑电荷的点缺陷处，整个群体中的细胞排列几乎是完美的。我们观察到新的细胞层优先在 +1/2 缺陷的位置形成，而空洞则优先在 -1/2 缺陷处出现。为了解释这些发现，我们将细菌菌落模拟为一种具有各向异性摩擦的可拉伸活性向列型流体。与我们的实验测量结果一致，该模型预测细胞会向 +1/2 缺陷处流入，从 -1/2 缺陷处流出。我们的结果表明，细胞运动性和细胞间的机械相互作用足以促进拓扑缺陷处细胞层的形成从而在该细菌菌落中催生子实体。
