Shaping nematic order in bacterial films with single-cell resolution patterning

TL;DR

This study demonstrates precise patterning of bacterial colonies to control nematic order, revealing how initial conditions influence collective dynamics and enabling the creation of optically anisotropic living materials.

Contribution

It introduces a method for single-cell resolution patterning of bacteria to manipulate nematic order and collective behavior in bacterial films.

Findings

Parallel seeding yields highly ordered nematic films

Ordered films buckle synchronously upon growth

Structural colouration and polarization are achieved through nematic alignment

Abstract

Bacterial colonies composed of elongated cells form active nematic fluids that spontaneously self-organise into ordered domains of aligned cells and exhibit self-generated chaotic flows powered by cell growth. While their dynamics have attracted significant attention, the role of initial conditions remains largely unexplored due to a lack of precise patterning methods. Here, we harness the precision of capillary assembly to pattern Bacillus subtilis endospores into arrays with controlled positions and orientations at single-cell resolution. Upon germination and growth of cell chains, we quantify the dynamics and morphologies of the resulting bacterial films. While orthogonally seeded spores lead to chaotic dynamics, seeding them with parallel orientations yields films with high nematic order across millimetres, which subsequently synchronously buckle upon further growth. Our observations are captured by numerical simulations and a model that describes the buckling dynamics starting from the mechanical properties of individual filaments. By programming local cell orientation with single-cell precision, we finally harness nematic alignment to create macroscopic bacterial films with local optical anisotropy, via structural colouration and light polarisation. Our findings demonstrate that initial conditions play a key role and offer exciting opportunities to control the spatio-temporal organization of bacterial assemblies towards addressing open biological questions and realizing living materials with tailored properties.