Morphogenesis of bacterial colonies in liquid crystalline environments

TL;DR

This study explores how liquid crystalline environments influence bacterial colony morphogenesis, revealing that elastic interactions induce alignment and buckling of bacterial chains, providing new mechanistic insights into bacterial behavior in complex fluids.

Contribution

It demonstrates experimentally and theoretically how liquid crystal elasticity guides bacterial chain formation and buckling, a novel insight into bacteria-LC interactions.

Findings

Bacteria form aligned chains in nematic liquid crystals.

Chains buckle when viscous stresses overcome LC elasticity.

LC elasticity influences bacterial colony morphology.

Abstract

Natural bacterial habitats are often complex fluids with viscoelastic and anisotropic responses to stress; for example, they can take the form of liquid crystals (LCs), with elongated microscopic constituents that collectively align while still retaining the ability to flow. However, laboratory studies typically focus on cells in simple liquids or complex fluids with randomly-oriented constituents. Here, we show how interactions with LCs shape bacterial proliferation in multicellular colonies. Using experiments, we find that in a nematic LC, cells generically form aligned single-cell-wide "chains" as they reproduce. As these chains lengthen, they eventually buckle in a highly localized manner. By combining our measurements with a continuum mechanical theory, we demonstrate that this distinctive morphogenetic program emerges because cells are kept in alignment due to the LC's elasticity; as each chain lengthens, growth-induced viscous stresses along its contour eventually overcome the elasticity of the surrounding nematic, leading to buckling. Our work thus reveals and provides mechanistic insight into the previously-overlooked role of LCs in sculpting bacterial life in complex environments.