Biophysics underlying the swarm to biofilm transition

TL;DR

This study investigates the transition from bacterial swarming to biofilm formation, revealing how physical clustering and biological processes interact to facilitate this change, challenging previous purely physical trigger hypotheses.

Contribution

The paper provides experimental evidence showing the combined role of biological and physical processes in the swarm to biofilm transition, highlighting the nucleation of aggregates and their influence.

Findings

Large, scale-free aggregates nucleate biofilm formation.

Physical processes like clustering and jamming accelerate the transition.

Purely physical effects are ruled out as sole triggers.

Abstract

Bacteria organize in a variety of collective states, from swarming, which has been attributed to rapid surface exploration, to biofilms, which are highly dense immobile communities attributed to stress resistance. It has been suggested that biofilm and swarming are oppositely controlled, making this transition particularly interesting for understanding the ability of bacterial colonies to adapt to challenging environments. Here, the swarm to biofilm transition is studied experimentally by analyzing the bacterial dynamics both on the individual and collective scales. We show that both biological and physical processes facilitate the transition - a few individual cells that initiate the biofilm program cause nucleation of large, scale-free stationary aggregates of trapped swarm cells. Around aggregates, cells continue swarming almost unobstructed, while inside, trapped cells slowly transform to biofilm. While our experimental findings rule out previously suggested purely physical effects as a trigger for biofilm formation, they show how physical processes, such as clustering and jamming, accelerate biofilm formation.