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A Mechanical Logic for Bacterial Navigation

Zeng, R.; Sacanna, S.; Saurabh, S.

2025-05-30 biophysics
10.1101/2025.05.27.656390 bioRxiv
Show abstract

Bacterial motility in unconfined liquids is well understood, but many species inhabit crowded, three-dimensional environments where physical constraints shape navigation. Here, we show that the aquatic bacterium Caulobacter crescentus employs backward swimming to overcome confinement, using a force-sensitive mechanism to control directional switching. Using colloidal "{micro}-Traps" to confine single cells within spherical volumes accessible through a narrow aperture, we reveal that cells engage backward motility to enter pores, explore boundaries, and escape confinement. This directional switching is gated by mechanical load: moderate forces on the flagellum promote backward motion, while excessive load suppresses it, preventing futile effort. This tunable, load-sensitive control offers direct evidence for a mechanical logic that governs motility: backward movement is activated when advantageous and disengaged when not. These findings highlight how physical forces influence microbial navigation and adaptation in complex environments.

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