Flagellin outer domain dimerization modulates motility in pathogenic and soil bacteria from viscous environments

Area of Science:

• Microbiology
• Structural Biology
• Biophysics

Background:

• Bacterial flagellar filaments are crucial for motility.
• Outer domains on flagellar filaments are structurally diverse and their roles are not fully understood.
• Supercoiling of flagellar filaments is essential for bacterial propulsion.

Purpose of the Study:

• To determine the atomic structures of flagellar filaments from various bacteria, including Escherichia coli O157:H7 and O127:H6.
• To investigate the structural organization and potential functions of outer domains in flagellar filaments.
• To understand how flagellar filament structure relates to bacterial motility in different environments.

Main Methods:

• Atomic cryo-electron microscopy (cryo-EM) was employed to resolve flagellar filament structures.
• Comparative structural analysis was performed on filaments from enterohemorrhagic E. coli O157:H7, enteropathogenic E. coli O127:H6, Achromobacter, and Sinorhizobium meliloti.
• Functional implications of observed structures were inferred based on bacterial habitats.

Main Results:

• Atomic cryo-EM structures revealed that outer domains dimerize or tetramerize, forming sheath or screw-like surfaces.
• These dimeric structures are formed by 180° rotations of half of the outer domains.
• The outer domain sheath (ODS) was shown to stabilize intermediate waveforms and prolong E. coli tumbling.

Conclusions:

• The dimerization of outer domains in flagellar filaments creates unique surface structures like sheaths and screw-like arrangements.
• The ODS plays a significant role in modulating bacterial motility by affecting waveform and tumbling.
• The prevalence of these structures in viscous environments suggests an adaptive advantage for bacteria in soil and intestinal habitats.