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Elife. 2017 Mar 6;6. pii: e23136. doi: 10.7554/eLife.23136.

Bacterial flagella grow through an injection-diffusion mechanism.

Author information

1
Junior Research Group, Infection Biology of <italic>Salmonella</italic>, Helmholtz Centre for Infection Research, Braunschweig, Germany.
2
Max Planck Institute for Infection Biology, Berlin, Germany.
3
Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan.
4
Institute of Science and Technology Austria, Klosterneuburg, Austria.
5
Department of Physics, Engineering Physics and Optics, Laval University, Quebec City, Quebec, Canada.
6
IBM Thomas J Watson Research Center, New York, United States.
7
RIKEN Quantitative Biology Center, Suita, Japan.
8
Department of Mathematics, University of Utah, Salt Lake City, United States.

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.

KEYWORDS:

Salmonella enterica; bacterial flagellum; biophysics; continuous-flow immunostaining; infectious disease; injection-diffusion mechanism; microbiology; proton motive force; structural biology

PMID:
28262091
PMCID:
PMC5386592
DOI:
10.7554/eLife.23136
[Indexed for MEDLINE]
Free PMC Article

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