Spontaneous chiral symmetry breaking in model bacterial suspensions

TL;DR

This study uses large-scale simulations to demonstrate how bacterial suspensions can spontaneously develop chiral structures from achiral interactions, revealing conditions for the emergence and growth of such chiral states.

Contribution

It introduces a simple 3D model of bacterial suspensions that captures spontaneous chiral symmetry breaking through active motion and hydrodynamics, supported by extensive simulations.

Findings

Chiral structures can emerge spontaneously in bacterial suspensions.

Conditions for the growth of chiral states are identified.

Hydrodynamic interactions play a key role in symmetry breaking.

Abstract

Chiral symmetry breaking is ubiquitous in biological systems, from DNA to bacterial suspensions. A key unresolved problem is how chiral structures may spontaneously emerge from achiral interactions. We study a simple model of bacterial suspensions in three dimensions that effectively incorporates active motion and hydrodynamic interactions. We perform large-scale molecular dynamics simulations (up to $10^6$ particles) and describe stable (or long-lived metastable) collective states that exhibit chiral organization although the interactions are achiral. We elucidate under which conditions these chiral states will emerge and grow to large scales. We also study a related equilibrium model that clarifies the role of orientational fluctuations.