Dps Protects Extra-chromosomal DNA in Escherichia coli: Grown to Early-stationary Phase from Hydrogen Peroxide Damage

DNA binding protein in starved cells (Dps) confers multiple modes of protection against various environmental stresses. This study investigated the protective role of Dps during oxidative stress to extra-chromosomal DNA by first transforming wildtype ZK126 and dps mutant ZK1146 E. coli cells with pKD46, a plasmid with temperature sensitive replicon, and then exposing the transformed cells to various concentrations of hydrogen peroxide. The frequency of the mutation of the temperature-sensitive gene to temperature insensitivity induced by hydrogen peroxide was determined by comparing the number of single colonies that arose at o o 30 C with the number of mutants that grew at 42 C. The mutation frequency to temperature insensitivity in the dps mutant strain was higher across all tested concentrations of hydrogen peroxide than the frequency in the wildtype strain, supporting the notion that Dps protects extra-chromosomal DNA. However, no clear correlation was observed between increasing hydrogen peroxide concentrations and increasing mutation frequency for either the wildtype or the dps mutant strains. This absence of trend may be due to the induction of other DNA repair mechanisms and should be further tested.