Propulsion Contribution from Individual Filament in Flagellar Bundle

TL;DR

This study investigates how individual filaments in flagellar bundles contribute to propulsion, revealing that total propulsion remains constant despite phase differences, with implications for understanding microbial movement and designing microswimmers.

Contribution

The paper introduces a combined experimental and numerical approach to analyze propulsion contributions of individual filaments in flagellar bundles, highlighting the effect of phase differences.

Findings

Total propulsion by two filaments is constant across phase differences.

Propulsion contribution from each filament varies with phase difference.

Only one filament drives propulsion at a phase difference of pi.

Abstract

Flagellated microorganisms overcome the low-Reynolds-number time reversibility by rotating helical flagella. For peritrichous bacteria, such as Escherichia coli, the randomly distributed flagellar filaments align along the same direction to form a bundle, facilitating complex locomotive strategies. To understand the process of flagella bundling, especially the propulsion force, we develop a multi-functional macroscopic experimental system and employ advanced numerical simulations for verification. Flagella arrangements and phase differences between helices are investigated, revealing the variation in propulsion contribution from the individual helix. Numerically, we build a time-dependent model to match the bundling process and study the influence of hydrodynamic interactions. Surprisingly, it is found that the total propulsion generated by a bundle of two filaments is constant at various phase differences between the helices. However, the difference between the propulsion from each helix is significantly affected by the phase difference, and only one of the helices is responsible for the total propulsion at a phase difference equals to pi. Through our experimental and computational results, we provide a new model considering the propulsion contribution of each filament to better understand microbial locomotion mechanisms, especially on the wobbling behavior of the cell. Our work also sheds light on the design and control of artificial microswimmers.