Bacterial DNA supercoiling and [ATP]/[ADP]. Changes associated with a transition to anaerobic growth

Shifting Escherichia coli from aerobic to anaerobic growth caused changes in the ratio of [ATP]/[ADP] and in negative supercoiling of chromosomal and plasmid DNA. Shortly after lowering oxygen tension, both [ATP]/[ADP] and supercoiling transiently decreased. Under conditions of exponential anaerobic growth, both were higher than under aerobic conditions. These correlations may reflect an effect of [ATP]/[ADP] on DNA gyrase, since in vitro [ATP]/[ADP] influences the level of plasmid supercoiling attained when gyrase is either introducing or removing supercoils. When the supercoiling activity of gyrase was perturbed by a mutation in gyrB, a shift to anaerobic conditions resulted in plasmid supercoil relaxation similar to that seen with wild-type. However, the low level of supercoiling in the mutant persisted during a time when supercoiling in wild-type recovered and then exceeded aerobic levels. Thus, changes in oxygen tension can alter DNA supercoiling through an effect on gyrase, and correlations exist between changes in supercoiling and changes in the intracellular ratio of [ATP]/[ADP].