Changes in the topological state of DNA during Escherichia coli adaptationto oxidative stress under glucose starvation and after the transition to growth

Changes in the topological state of DNA occur in a starving Escherichia col i culture under oxidative stress caused by the addition of hydrogen peroxid e. The addition of a carbon and energy source to this culture results in a second stress reaction. This supports previous data indicating that differe nt mechanisms are responsible for the cell defense against oxidative stress in exponential and starving E. coil cultures. Polyamine synthesis is invol ved in the cell adaptation to the stress. Putrescine binding to DNA and its dissociation seem to modulate the DNA topological state, which regulates t he expression of the adaptive genes. An increase in the activity of the pol yamine-synthesizing system in response to oxidative stress leads to a putre scine flux across the cytoplasmic membrane, due to which the antioxidant ac tivity of putrescine protects the membrane phospholipids and contributes to the restoration of the cell energy-generating function.