Geometry and Mechanics of Microdomains in Growing Bacterial Colonies

By Zhihong You, D. Pearce, A. Sengupta, L. Giomi. Physical Review X, 2017

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Bacterial colonies are abundant on living and non-living surfaces and are known to mediate a broad range of processes in ecology, medicine and industry. Although extensively researched, from single cells to demographic scales, a comprehensive biomechanical picture, highlighting the cell-to-colony dynamics, is still lacking. Here, using molecular dynamics simulations and continuous modelling, we investigate the geometrical and mechanical properties of a bacterial colony growing on a substrate with free boundary, and demonstrate that such an expanding colony self-organizes into a "mosaic" of micro-domains consisting of highly aligned cells. The emergence of micro-domains is mediated by two competing forces: the steric forces between neighboring cells which favour cell alignment, and the extensile stresses due to cell growth that tend to reduce the local orientational order, and thereby distort the system. This interplay results into an exponential distribution of the domain areas, and sets a characteristic length scale proportional to the square root of the ratio between the system orientational stiffness and the magnitude of the extensile active stress. Finally, our examination of the internal stresses reveal that, in addition to biochemical pathways, the spatiotemporal organization in microbial colonies is significantly affected by the mechanical forces exerted and experienced by the growing cells.

Subfields: Cell Biology, Ecology, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/70016ecf90302e33fad4ebb4faebd9f3266b7b5b