Non-equilibrium dynamics of bacterial colonies-growth, active fluctuations, segregation, adhesion, and invasion

K Zhou and M Hennes and B Maier and G Gompper and B Sabass, COMMUNICATIONS PHYSICS, 5, 251 (2022).

DOI: 10.1038/s42005-022-01018-7

Adhesion forces due to active pili govern the formation of biofilms by a wide range of bacteria. Using simulations, this work shows how such active adhesions determine the morphology of bacterial collectives, their non-equilibrium fluctuations, and the spreading dynamics in different geometries. Colonies of bacteria endowed with a pili-based self-propulsion machinery are ideal models for investigating the structure and dynamics of active many-particle systems. We study Neisseria gonorrhoeae colonies with a molecular-dynamics-based approach. A generic, adaptable simulation method for particle systems with fluctuating bond-like interactions is devised. The simulations are employed to investigate growth of bacterial colonies and the dependence of the colony structure on cell-cell interactions. In colonies, pilus retraction enhances local ordering. For colonies consisting of different types of cells, the simulations show a segregation depending on the pili-mediated interactions among different cells. These results agree with experimental observations. Next, we quantify the power-spectral density of colony-shape fluctuations in silico. Simulations predict a strong violation of the equilibrium fluctuation-response relation. Furthermore, we show that active force generation enables colonies to spread on surfaces and to invade narrow channels. The methodology can serve as a foundation for future studies of active many-particle systems at boundaries with complex shape.

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