Molecular architecture of the bacterial flagellar motor in cells

Biochemistry. 2014 Jul 15;53(27):4323-33. doi: 10.1021/bi500059y. Epub 2014 Jul 1.


The flagellum is one of the most sophisticated self-assembling molecular machines in bacteria. Powered by the proton-motive force, the flagellum rapidly rotates in either a clockwise or counterclockwise direction, which ultimately controls bacterial motility and behavior. Escherichia coli and Salmonella enterica have served as important model systems for extensive genetic, biochemical, and structural analysis of the flagellum, providing unparalleled insights into its structure, function, and gene regulation. Despite these advances, our understanding of flagellar assembly and rotational mechanisms remains incomplete, in part because of the limited structural information available regarding the intact rotor-stator complex and secretion apparatus. Cryo-electron tomography (cryo-ET) has become a valuable imaging technique capable of visualizing the intact flagellar motor in cells at molecular resolution. Because the resolution that can be achieved by cryo-ET with large bacteria (such as E. coli and S. enterica) is limited, analysis of small-diameter bacteria (including Borrelia burgdorferi and Campylobacter jejuni) can provide additional insights into the in situ structure of the flagellar motor and other cellular components. This review is focused on the application of cryo-ET, in combination with genetic and biophysical approaches, to the study of flagellar structures and its potential for improving the understanding of rotor-stator interactions, the rotational switching mechanism, and the secretion and assembly of flagellar components.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Bacteria / cytology
  • Bacteria / metabolism*
  • Bacterial Physiological Phenomena
  • Bacterial Proteins / metabolism
  • Cryoelectron Microscopy
  • Electron Microscope Tomography
  • Flagella / physiology*
  • Flagella / ultrastructure
  • Protein Conformation
  • Species Specificity
  • Spirochaetales / cytology
  • Spirochaetales / metabolism


  • Bacterial Proteins
  • Flig protein, Bacteria
  • FliM protein, Bacteria