Cell-scale confinement reorders bacterial speed rankings

Channel width and other confinement parameters reorder which bacterium swims fastest, with Vibrio alginolyticus dropping to ~4 m/s in 1.25-m channels.

• Why it matters: Speed rankings from open liquid may not reflect bacterial performance in pores, mucus, and host passages where space is cell-scale and motility constraints differ.
• What they did: Using a microfluidic device with eight channel widths (0.80–3.00 m) in one field of view, the authors tracked unlabeled cells of eight species spanning five motility systems while varying chamber height and a polymer additive.
• The result: Chamber height, polymer additive, and channel width each reordered rankings; open-liquid speed did not predict robustness, and in two lineages symbionts (Caballeronia insecticola, Vibrio fischeri) outpaced non-symbiotic relatives in narrow channels.

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