Swimming Efficiently by Wrapping

TL;DR

This study investigates how single-flagellated bacteria switch between swimming modes, revealing that the wrapped mode, though slower in bulk, becomes more efficient under confinement due to hydrodynamic effects and a screw-like mechanism.

Contribution

It provides new insights into the hydrodynamics of bacterial swimming modes, especially under confinement, highlighting the efficiency of the wrapped mode in such environments.

Findings

Wrapped mode is slower in bulk but more efficient under confinement.

Hydrodynamic coupling enhances the wrapped mode's efficiency in tight spaces.

The wrapped mode exhibits an Archimedes' screw-like fluid movement.

Abstract

Single flagellated bacteria are ubiquitous in nature. They exhibit various swimming modes using their flagella to explore complex surroundings such as soil and porous polymer networks. Some single-flagellated bacteria swim with two distinct modes, one with its flagellum extended away from its body and another with its flagellum wrapped around it. The wrapped mode has been observed when bacteria swim under tight confinements or in highly viscous polymeric melts. In this study we investigate the hydrodynamics of these two modes inside a circular pipe. We find that the wrapped mode is slower than the extended mode in bulk but more efficient under strong confinement due to a hydrodynamic increase of its flagellum translation-rotation coupling and an Archimedes' screw-like configuration that helps to move the fluid along the pipe.