title: Bacterial flagella grow through an injection-diffusion mechanism.
abstract: 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.
authors.affiliation: Junior Research Group, Infection Biology of <italic>Salmonella</italic>, Helmholtz Centre for Infection Research, Braunschweig, Germany.|Max Planck Institute for Infection Biology, Berlin, Germany.
authors.forename: Thibaud T
authors.identifier: 0000-0002-1530-2613
authors.initials: TT
authors.lastname: Renault
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan.
authors.forename: Anthony O
authors.identifier: 0000-0002-8710-1351
authors.initials: AO
authors.lastname: Abraham
authors.affiliation: Institute of Science and Technology Austria, Klosterneuburg, Austria.
authors.forename: Tobias
authors.initials: T
authors.lastname: Bergmiller
authors.affiliation: Department of Physics, Engineering Physics and Optics, Laval University, Quebec City, Quebec, Canada.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Paradis
authors.affiliation: Department of Physics, Engineering Physics and Optics, Laval University, Quebec City, Quebec, Canada.
authors.forename: Simon
authors.initials: S
authors.lastname: Rainville
authors.affiliation: Max Planck Institute for Infection Biology, Berlin, Germany.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Charpentier
authors.affiliation: Institute of Science and Technology Austria, Klosterneuburg, Austria.
authors.forename: Călin C
authors.identifier: 0000-0001-6220-2052
authors.initials: CC
authors.lastname: Guet
authors.affiliation: IBM Thomas J Watson Research Center, New York, United States.
authors.forename: Yuhai
authors.initials: Y
authors.lastname: Tu
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan.|RIKEN Quantitative Biology Center, Suita, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Namba
authors.affiliation: Department of Mathematics, University of Utah, Salt Lake City, United States.
authors.forename: James P
authors.initials: JP
authors.lastname: Keener
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Minamino
authors.affiliation: Junior Research Group, Infection Biology of <italic>Salmonella</italic>, Helmholtz Centre for Infection Research, Braunschweig, Germany.
authors.forename: Marc
authors.identifier: 0000-0001-6292-619X
authors.initials: M
authors.lastname: Erhardt
mesh_terms: D005407:Flagella / Q000378:metabolism*; D005408:Flagellin / Q000378:metabolism*; D008962:Models, Theoretical; D001678:Organelle Biogenesis; D018892:Proton-Motive Force; D019779:Salmonella enterica / Q000378:metabolism*
chemical_list: D005408:Flagellin
keywords: Salmonella enterica; bacterial flagellum; biophysics; continuous-flow immunostaining; infectious disease; injection-diffusion mechanism; microbiology; proton motive force; structural biology