A new mode of swimming in singly flagellated Pseudomonas aeruginosa

Significance

The monotrichous Pseudomonas aeruginosa was usually thought to swim in a pattern of “run and reverse” (possibly with pauses in between), where straight runs alternated with reverses with angular changes of swimming direction near 180°. Here, by simultaneously tracking the cell swimming and the morphology of its flagellum, we discovered a swimming mode in P. aeruginosa—the wrap mode, during which the flagellar filament wrapped around the cell body and induced large fluctuation of the body orientation. The wrap mode randomized swimming direction, resulting in a broad distribution of angular changes over 0 to 180° with a peak near 90°. This allowed the bacterium to explore the environment more efficiently, which we confirmed by stochastic simulations of P. aeruginosa chemotaxis.

Abstract

Bacterial motility and chemotaxis are important for many biological processes such as the exploration of the environment and the spreading of bacterial infections. Different bacterial species usually adopt different swimming strategies. As an opportunistic pathogen, the singly flagellated Pseudomonas aeruginosa was recently found to swim in a “run–reverse” or “run–reverse–pause” pattern. Here, by simultaneously tracking the position of the cell body and the conformation of its flagellum, we discovered a swimming mode—the wrap mode, during which the filament wrapped around the cell body. We measured the behavioral characteristics of the wrap mode and found that it randomized the swimming direction, thereby allowing the bacterium to explore its neighborhood efficiently. We confirmed by stochastic simulations of P. aeruginosa chemotaxis that the wrap mode enhanced its chemotaxis performance. Therefore, the wrap mode we discovered here represents an efficient strategy for polar-flagellated bacteria to explore the environment.