Topological defects promote layer formation in Myxococcus xanthus colonies
Topological defects promote layer formation in Myxococcus xanthus colonies
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DOI：
10.1038/s41567-020-01056-4
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发表时间：
2020-11-23
期刊：
影响因子：
19.6
通讯作者：
Shaevitz, Joshua W.
中科院分区：
文献类型：
--
作者：
Copenhagen, Katherine;Alert, Ricard;Shaevitz, Joshua W.
土壤细菌黄粘球菌生活在密集的群体中，形成动态的三维模式以响应环境变化，例如饥饿期间的水滴状子实体(1)。这些多细胞结构的发育始于细胞层的顺序形成，这一过程目前尚不清楚(2)。在这里，利用共焦三维成像，我们发现活动的棒状 M. xanthus 细胞在每一层中紧密排列和排列，形成活性向列液晶。除了带有半整数拓扑电荷的点缺陷外，整个群体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，而孔优先在 -1/2 缺陷的位置打开。为了解释这些发现，我们将细菌菌落建模为具有各向异性摩擦的可拉伸活性向列液。与我们的实验测量一致，该模型预测细胞将流入 +1/2 缺陷，并预测细胞将从 -1/2 缺陷流出。我们的研究结果表明，细胞运动和机械细胞间相互作用足以促进拓扑缺陷处细胞层的形成，从而在黄花菌菌落中播种子实体。活性向列系统（如上皮组织和神经祖细胞）的拓扑缺陷可能与生物功能相关。在这里，作者表明，缺陷可以在土壤细菌黄粘球菌的层形成中发挥作用。
The soil bacterium Myxococcus xanthus lives in densely packed groups that form dynamic three-dimensional patterns in response to environmental changes, such as droplet-like fruiting bodies during starvation(1). The development of these multicellular structures begins with the sequential formation of cell layers in a process that is poorly understood(2). Here, using confocal three-dimensional imaging, we find that motile, rod-shaped M. xanthus 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 towards the +1/2 defects and an outflux of cells from the -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 M. xanthus.Topological defects in active nematic systems such as epithelial tissues and neural progenitor cells can be associated with biological functions. Here, the authors show that defects can play a role in the layer formation of the soil bacterium Myxococcus xanthus.