DNA supercoiling differences in bacteria result from disparate DNA gyrase activation by polyamines

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• DNA supercoiling is crucial for cellular processes, regulated by opposing enzymes: topoisomerase I (relaxes DNA) and DNA gyrase (compacts DNA).
• Escherichia coli and Salmonella enterica serovar Typhimurium, despite high amino acid identity in these enzymes, exhibit different DNA supercoiling patterns.
• The reason for differing DNA supercoiling in these closely related bacteria under identical conditions remained unexplained.

Purpose of the Study:

• To investigate the molecular basis for the distinct DNA supercoiling observed between Escherichia coli and Salmonella.
• To elucidate the role of polyamines, specifically spermidine and putrescine, in the differential activation of bacterial DNA gyrase.
• To identify potential targets for novel antibacterial agents by understanding DNA supercoiling regulation.

Main Methods:

• In vitro enzymatic assays to assess DNA gyrase activity in response to varying polyamine concentrations.
• In vivo experiments in E. coli and Salmonella to observe DNA supercoiling under different polyamine and magnesium conditions.
• Comparative analysis of DNA gyrase activation mechanisms between the two bacterial species.

Main Results:

• Salmonella DNA gyrase activity was sensitive to physiological putrescine concentrations, unlike E. coli DNA gyrase.
• In vivo, putrescine activated Salmonella DNA gyrase, while spermidine activated E. coli DNA gyrase.
• Elevated extracellular magnesium selectively reduced DNA supercoiling in Salmonella by lowering putrescine levels.

Conclusions:

• Disparate activation of DNA gyrase by spermidine and putrescine explains the differing DNA supercoiling in E. coli and Salmonella.
• A novel signal transduction pathway regulating DNA supercoiling via polyamine-gyrase interaction has been defined.
• The identified polyamine-gyrase interactions represent potential targets for developing new antibacterial strategies.