Bacterial DNA supercoiling and [ATP]/[ADP] ratio: changes associated with salt shock

Area of Science:

• Molecular Biology
• Microbiology
• Biophysics

Background:

• DNA supercoiling is crucial for various cellular processes, including replication and transcription.
• The enzyme DNA gyrase is responsible for introducing negative supercoils into DNA.
• Cellular energy status, indicated by the [ATP]/[ADP] ratio, is known to influence enzymatic activity.

Purpose of the Study:

• To investigate the dynamic changes in DNA supercoiling and cellular energy levels in Escherichia coli K-12 upon exposure to salt stress.
• To determine the relationship between the intracellular [ATP]/[ADP] ratio and plasmid DNA supercoiling under osmotic stress.

Main Methods:

• Escherichia coli K-12 cells were subjected to a shift from a low-salt to a high-salt (0.5 M NaCl) medium.
• Intracellular [ATP]/[ADP] ratios were measured.
• Plasmid DNA negative supercoiling levels were assessed.

Main Results:

• A rapid, transient increase in both the [ATP]/[ADP] ratio and plasmid DNA negative supercoiling was observed within minutes of salt shock.
• Following the initial rise, both parameters decreased, stabilizing at levels slightly above those in non-stressed cells.
• The observed physiological response suggests a direct correlation between cellular energy charge and DNA supercoiling.

Conclusions:

• The intracellular [ATP]/[ADP] ratio is a key regulator of DNA supercoiling in Escherichia coli during salt stress.
• DNA gyrase activity is sensitive to fluctuations in the [ATP]/[ADP] ratio, mediating the observed supercoiling changes.
• This study highlights the importance of cellular energy status in controlling DNA topology under environmental stress.