Abstract
Individual swimming bacteria are known to bias their random trajectories in search of food and to optimize survival. The motion of bacteria within a swarm, wherein they migrate as a collective group over a solid surface, is fundamentally different as typical bacterial swarms show large-scale swirling and streaming motions involving millions to billions of cells. Here by tracking trajectories of fluorescently labelled individuals within such dense swarms, we find that the bacteria are performing super-diffusion, consistent with Lévy walks. Lévy walks are characterized by trajectories that have straight stretches for extended lengths whose variance is infinite. The evidence of super-diffusion consistent with Lévy walks in bacteria suggests that this strategy may have evolved considerably earlier than previously thought.
Highlights
Individual swimming bacteria are known to bias their random trajectories in search of food and to optimize survival
Our results reveal that the trajectories of swarming cells are super-diffusive, performing a Levy walk (LW)
Swimming bacteria move by a process called run-and-tumble, in which short random movements are interspersed by long trajectories
Summary
Individual swimming bacteria are known to bias their random trajectories in search of food and to optimize survival. The second approach applied video analysis methods (particle image velocimetry or optical flow)[8] to obtain either short individual trajectories (up to B1 s; refs 10,13,16) or a locally averaged velocity field describing the collective dynamics of groups and clusters These methods cannot resolve the individual motion of bacteria to provide long-time trajectories of individuals. The LW model is a continuous-time random walk in which particles move with a fixed speed, making sharp turns at random times with a power-law distribution[42] As a result, these processes are characterized by trajectories that have straight stretches for extended lengths whose variance is infinite[43,44,45]. We show for the first time observations of swarming bacteria performing random motion consistent with LW behaviour
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