The process by which bacterial cells build their intricate flagellar motility apparatuses has long fascinated scientists. Our understanding of this process comes mainly from studies of purified flagella from two species, Escherichia coli and Salmonella enterica. Here, we used electron cryo-tomography (cryo-ET) to image the assembly of the flagellar motor in situ in diverse Proteobacteria: Hylemonella gracilis, Helicobacter pylori, Campylobacter jejuni, Pseudomonas aeruginosa, Pseudomonas fluorescens, and Shewanella oneidensis. Our results reveal the in situ structures of flagellar intermediates, beginning with the earliest flagellar type III secretion system core complex (fT3SScc) and MS-ring. In high-torque motors of Beta-, Gamma-, and Epsilon-proteobacteria, we discovered novel cytoplasmic rings that interact with the cytoplasmic torque ring formed by FliG. These rings, associated with the MS-ring, assemble very early and persist until the stators are recruited into their periplasmic ring; in their absence the stator ring does not assemble. By imaging mutants in Helicobacter pylori, we found that the fT3SScc proteins FliO and FliQ are required for the assembly of these novel cytoplasmic rings. Our results show that rather than a simple accretion of components, flagellar motor assembly is a dynamic process in which accessory components interact transiently to assist in building the complex nanomachine.
|State||Published - May 16 2022|
Bibliographical noteFunding Information:
This project was funded by the NIH (grant R01 AI127401 to G.J.J and NIH P20 GM130456 to C.L.S.) and a Baxter postdoctoral fellowship from Caltech to M.K. Cryo‐ET work was performed in the Beckman Institute Resource Center for Transmission Electron Microscopy at the California Institute of Technology. We are grateful to Prof. Marc Erhardt (Humboldt‐Universität zu Berlin) for critically reading an initial version of this work.
© 2022 The Authors.
- bacterial flagellar motor
ASJC Scopus subject areas
- Neuroscience (all)
- Molecular Biology
- Biochemistry, Genetics and Molecular Biology (all)
- Immunology and Microbiology (all)