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The role of cAMP in flagellation of Salmonella typhimurium
Abstract:
A mutational alteration either in adenylate cyclase (cya-) or in cyclic-3'5'-AMP (cAMP) receptor protein (crp-) rendered Salmonella typhimurium incapable of producing flagella. The amount of mRNA specific for flagellin in these mutants was almost negligible when assayed in an in vitro protein synthesizing system. A secondary mutation cfs, partially suppressing the cya- mutation, was identified among the revertants of cya-. A mutation in the same cistron as cfs resulted in a non-flagellate phenotype either by itself or in combination with cfs. The cistron, which was given the gene symbol flaT, was located between flaE and flaL. It was suggested that cAMP receptor protein together with cAMP modulates the gene flaT, which in turn acts as a positive effector on the synthesis of active mRNA specific for flagellin.
Insights
Mutations in adenylate cyclase or cAMP receptor protein prevent Salmonella flagella production. A newly identified gene, flaT, acts as a positive regulator for flagellin mRNA synthesis.
Area of Science:
- Bacterial genetics
- Molecular microbiology
- Signal transduction
Background:
- Flagellar synthesis is crucial for bacterial motility and virulence in Salmonella typhimurium.
- Cyclic AMP (cAMP) and its receptor protein (CRP) are known regulators of gene expression in bacteria.
- Previous studies indicated a role for cAMP-CRP in regulating Salmonella flagellar gene expression.
Purpose of the Study:
- To investigate the role of adenylate cyclase (cya) and cAMP receptor protein (crp) in Salmonella flagellar biosynthesis.
- To identify and characterize genetic factors involved in the regulation of flagellin mRNA synthesis.
- To elucidate the regulatory pathway controlling flagellar gene expression in Salmonella.
Main Methods:
- Isolation and characterization of Salmonella typhimurium mutants defective in flagellar production.
- Genetic analysis including complementation tests and gene mapping to identify mutations.
- In vitro protein synthesis assays to quantify flagellin-specific mRNA levels.
Main Results:
- Mutations in cya or crp abolished flagellar production and significantly reduced flagellin mRNA levels.
- A secondary mutation, cfs, was identified that partially suppressed the cya mutation.
- A novel gene, flaT, was identified and mapped; mutations in flaT also resulted in a non-flagellate phenotype.
Conclusions:
- The cAMP-CRP complex positively modulates the expression of the flaT gene in Salmonella.
- The flaT gene product acts as a positive effector, essential for the synthesis of active flagellin mRNA.
- This study reveals a key regulatory step in the pathway controlling flagellar biosynthesis in Salmonella typhimurium.