Bundling instability of lophotrichous bacteria

TL;DR

This paper develops a mathematical model to understand how lophotrichous bacteria like Pseudomonas putida swim using bundled flagella, revealing diverse motility modes influenced by hydrodynamics and flagellar elasticity.

Contribution

It introduces a new mathematical framework capturing the coordination and hydrodynamic interactions of multiple flagella in bacteria, linking physical properties to motility modes.

Findings

Identification of distinct bundled and unbundled flagella configurations.

Demonstration of how hydrodynamic interactions influence motility regimes.

Analysis of stable bundle characteristics and their impact on swimming behavior.

Abstract

We present a mathematical model of lophotrichous bacteria, motivated by Pseudomonas putida, which swim through fluid by rotating a cluster of multiple flagella extended from near one pole of the cell body. Although the flagella rotate individually, they are typically bundled together, enabling the bacterium to exhibit three primary modes of motility: push, pull, and wrapping. One key determinant of these modes is the coordination between motor torque and rotational direction of motors. The computational variations in this coordination reveal a wide spectrum of dynamical motion regimes, which are modulated by hydrodynamic interactions between flagellar filaments. These dynamic modes can be categorized into two groups based on the collective behavior of flagella, i.e., bundled and unbundled configurations. For some of these configurations, experimental examples from fluorescence microscopy recordings of swimming P. putida cells are also presented. Furthermore, we analyze the characteristics of stable bundles, such as push and pull, and investigate the dependence of swimming behaviors on the elastic properties of the flagella.