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

TL;DR

This study uses molecular dynamics simulations to explore the growth, structure, and invasion behaviors of bacterial colonies, revealing how active forces and cell interactions influence colony dynamics and shape fluctuations.

Contribution

It introduces a versatile simulation method for active particle systems with fluctuating bonds and applies it to bacterial colonies, highlighting the role of pili in colony organization and invasion.

Findings

Pilus retraction enhances local order within colonies.

Segregation occurs based on pili-mediated interactions among different cell types.

Active force generation enables colonies to invade narrow channels.

Abstract

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.