Active Spaghetti: Collective Organization in Cyanobacteria

TL;DR

This study explores how cyanobacteria colonies self-organize through collective filament behavior, revealing a transition from random to reticulate patterns driven by physical interactions and motility, modeled by a minimal active filament framework.

Contribution

We introduce a nonreciprocal active filament model that explains the collective organization and pattern formation in cyanobacteria colonies based on experimental observations.

Findings

Filament colonies transition from isotropic to reticulate patterns with increasing density.

The minimal model reproduces observed behaviors and explains the characteristic lengthscale.

Pattern formation depends on the Peclet number of the filaments.

Abstract

Filamentous cyanobacteria can show fascinating examples of nonequilibrium self-organization, which however are not well-understood from a physical perspective. We investigate the motility and collective organization of colonies of these simple multicellular lifeforms. As their area density increases, linear chains of cells gliding on a substrate show a transition from an isotropic distribution to bundles of filaments arranged in a reticulate pattern. Based on our experimental observations of individual behavior and pairwise interactions, we introduce a nonreciprocal model accounting for the filaments' large aspect ratio, fluctuations in curvature, motility, and nematic interactions. This minimal model of active filaments recapitulates the observations, and rationalizes the appearance of a characteristic lengthscale in the system, based on the Peclet number of the cyanobacteria filaments.