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Elife. 2019 Jan 16;8. pii: e43487. doi: 10.7554/eLife.43487.

The presence and absence of periplasmic rings in bacterial flagellar motors correlates with stator type.

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Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States.
Department of Physics and Astronomy, Biological Sciences, and Chemistry, University of Southern California, Los Angeles, United States.
Howard Hughes Medical Institute, California Institute of Technology, Pasadena, United States.


The bacterial flagellar motor, a cell-envelope-embedded macromolecular machine that functions as a cellular propeller, exhibits significant structural variability between species. Different torque-generating stator modules allow motors to operate in different pH, salt or viscosity levels. How such diversity evolved is unknown. Here, we use electron cryo-tomography to determine the in situ macromolecular structures of three Gammaproteobacteria motors: Legionella pneumophila, Pseudomonas aeruginosa, and Shewanella oneidensis, providing the first views of intact motors with dual stator systems. Complementing our imaging with bioinformatics analysis, we find a correlation between the motor's stator system and its structural elaboration. Motors with a single H+-driven stator have only the core periplasmic P- and L-rings; those with dual H+-driven stators have an elaborated P-ring; and motors with Na+ or Na+/H+-driven stators have both their P- and L-rings embellished. Our results suggest an evolution of structural elaboration that may have enabled pathogenic bacteria to colonize higher-viscosity environments in animal hosts.


Legionella pneumophila; Pseudomonas aeruginosa; Shewanella oneidensis MR-1; bacterial flagellar motor; electron cryo-tomography; evolution; evolutionary biology; infectious disease; microbiology

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