Long-range nematic order and anomalous fluctuations in suspensions of swimming filamentous bacteria

TL;DR

This study demonstrates that filamentous bacteria in confined environments can exhibit long-range nematic order and giant number fluctuations, aligning with theoretical flocking models.

Contribution

It provides experimental evidence of long-range nematic order and anomalous fluctuations in bacterial suspensions, confirming predictions of flocking models.

Findings

Observation of global nematic order in bacterial suspensions

Detection of giant number fluctuations

Confirmation of theoretical flocking model predictions

Abstract

We study the collective dynamics of elongated swimmers in a very thin fluid layer by devising long, filamentous, non-tumbling bacteria. The strong confinement induces weak nematic alignment upon collision, which, for large enough density of cells, gives rise to global nematic order. This homogeneous but fluctuating phase, observed on the largest experimentally-accessible scale of millimeters, exhibits the properties predicted by standard models for flocking such as the Vicsek-style model of polar particles with nematic alignment: true long-range nematic order and non-trivial giant number fluctuations.