Decoding Bacterial Motility: From Swimming States to Patterns and Chemotactic Strategies

Abstract

The bacterial flagellum serves as a crucial propulsion apparatus for motility and chemotaxis. Bacteria employ complex swimming patterns to perform essential biological tasks. These patterns involve transitions between distinct swimming states, driven by flagellar motor rotation, filament polymorphism, and variations in flagellar arrangement and configuration. Over the past two decades, advancements in fluorescence staining technology applied to bacterial flagella have led to the discovery of diverse bacterial movement states and intricate swimming patterns. This review provides a comprehensive overview of nano-filament observation methodologies, swimming states, swimming patterns, and the physical mechanisms underlying chemotaxis. These novel insights and ongoing research have the potential to inspire the design of innovative active devices tailored for operation in low-Reynolds-number environments.

Keywords: bacterial flagellar motility; flagellar polymorphism; swimming pattern; swimming state.

Figure 1

The complexity of bacterial motility and the simplicity of chemotaxis behavior. Bacterial chemotaxis integrates signal transduction with locomotion. Locomotion is influenced by motor rotation, flagellar polymorphism, flagellar arrangement, and configuration. These factors collectively determine specific swimming modes, while a swimming pattern consists of a series of such modes. Bacteria modulate the states within a swimming pattern to perform random walks and biased random walks.

Figure 2

The observation of flagellar filaments. (A) Fluorescence labeling using fluorophore-linked succinimydyl (NHS) esters (box a), a TC-tag (box b), and a sheath (box c). (B) Schematics of the EPI and TIRF fluorescence imaging of a sheathed bacterium V. alginolyticus moving near the surface. The cell is labeled with FM 4-64. (C) For rapidly rotating flagellar filaments, long excitation times result in blurred images. Strobe illumination provides clear images of filament configurations. The cells are sheathed A. fisheri labeled with FM 4-64.

Figure 3

The decomposition of swimming states. (A) Flagellar motor rotation states: CCW, CW, and STOP. (B) Flagellar filament polymorphism. (C) Five major flagellar filament arrangements. (D) Flagellar configuration. (E) Swimming modes. (F) Run-mode swimming directions and swimming states.

Figure 4

Kinetic model for swimming patterns. (A) Run-and-tumble. (B) Push–pull–flick.

Figure 5

Kinetic model for swimming patterns. (A) Typical wrap-mode transition. The wrapping event occurs during the motor rotation transition from CCW to CW. (B) P. aeruginosa wrap-mode transition. The wrapping event occurs after the pull mode resumes CCW rotation. This is similar to the flick mode of V. alginolyticus.

Figure 6

Kinetic model for swimming pattern in wrap mode. (A) A. fischeri swimming pattern with wrap mode. (B) The flagellar filament polymorphic transition during wrap mode is induced by flagellar motor switching. Reproduced with permission from CJLo [26]; published by Physical Review Research, 2024.

Figure 7

The collection of known bacterial swimming modes and possible transitions. It shows the limited routes of the transitions.