TY - JOUR AB - The bacterial flagellum is a self-assembling nanomachine. The external flagellar filament, several times longer than a bacterial cell body, is made of a few tens of thousands subunits of a single protein: flagellin. A fundamental problem concerns the molecular mechanism of how the flagellum grows outside the cell, where no discernible energy source is available. Here, we monitored the dynamic assembly of individual flagella using in situ labelling and real-time immunostaining of elongating flagellar filaments. We report that the rate of flagellum growth, initially ~1,700 amino acids per second, decreases with length and that the previously proposed chain mechanism does not contribute to the filament elongation dynamics. Inhibition of the proton motive force-dependent export apparatus revealed a major contribution of substrate injection in driving filament elongation. The combination of experimental and mathematical evidence demonstrates that a simple, injection-diffusion mechanism controls bacterial flagella growth outside the cell. AU - Renault, Thibaud AU - Abraham, Anthony AU - Bergmiller, Tobias AU - Paradis, Guillaume AU - Rainville, Simon AU - Charpentier, Emmanuelle AU - Guet, Calin C AU - Tu, Yuhai AU - Namba, Keiichi AU - Keener, James AU - Minamino, Tohru AU - Erhardt, Marc ID - 655 JF - eLife SN - 2050084X TI - Bacterial flagella grow through an injection diffusion mechanism VL - 6 ER -