Flagellar assembly in Salmonella typhimurium: analysis with temperature-sensitive mutants

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Motility

Background:

• Bacterial flagella are complex molecular machines essential for motility.
• Understanding flagellar assembly is crucial for deciphering bacterial pathogenesis and developing targeted therapies.

Purpose of the Study:

• To investigate the sequential order of protein incorporation during flagellar assembly in Salmonella typhimurium.
• To identify previously unknown proteins involved in flagellar structure formation.

Main Methods:

• Utilized temperature-sensitive mutants of Salmonella typhimurium.
• Employed a dual-phase radiolabeling strategy with restrictive and permissive temperatures.
• Purified flagellar hook-basal body complexes for analysis via gel electrophoresis and autoradiography.

Main Results:

• Identified the M-ring protein (FliF) as an early stable component, along with novel 23 and 26 kDa proteins.
• Demonstrated independent synthesis and export of P-ring (FlgI) and L-ring (FlgH) proteins.
• Elucidated the sequential export and assembly of rod proteins (FlgB, FlgC, FlgF, FlgG) via a flagellum-specific pathway.
• Showed that rod assembly requires flhA and fliI genes and stabilization upon P-ring addition.
• Confirmed the successive export and assembly of hook and filament proteins.

Conclusions:

• The M-ring protein is incorporated early in flagellar assembly.
• Rod proteins are exported and assembled sequentially via a dedicated pathway.
• P and L rings assemble around the completed rod structure.
• Hook and filament assembly follows rod and ring formation, dependent on the flagellar master operon.