Assembling flagella in Salmonella mutant strains producing a type III export apparatus without FliO

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Genetics

Background:

• The Salmonella flagellum's type III export apparatus is crucial for motility.
• Deletion of the fliO gene impairs flagellar assembly and motility.
• Suppressor mutations in fliP can partially restore motility in fliO mutants.

Purpose of the Study:

• To elucidate the mechanism of motility rescue in Salmonella fliO deletion mutants.
• To identify novel suppressor mutations and understand their role in flagellar assembly.

Main Methods:

• Isolation and whole-genome sequencing of suppressor mutant strains.
• Genetic analysis involving gene deletions and plasmid complementation.
• Molecular techniques including gene fusion assays, immunoblot analysis, and quantitative real-time reverse transcriptase PCR.

Main Results:

• Identified missense mutations in clpP [clpP(V20F)] and synonymous mutations in fliA [fliA(+36T→C)] as novel suppressors.
• Combined clpP(V20F) or fliA(+36T→C) mutations with fliP mutations additively rescued motility and flagellar biosynthesis in fliO deletion strains.
• The fliA(+36T→C) mutation enhanced mRNA translation and increased σ(28) levels, rescuing class 3 flagellar gene expression.

Conclusions:

• The clpP and fliA suppressor mutations, along with fliP mutations, collectively restore flagellar function in fliO mutants.
• FliO's function is closely linked to the regulation of FliP during flagellar assembly.
• This study reveals complex regulatory interactions governing flagellar export apparatus assembly and function.