Upon entering host cell bacteriophage λ can take one of two alternative developemental pathways: lytic or lysogenic. If phage enters lysogenic cycle it’s DNA is integrated with host’s chromosome in the form of a prophage. This prophage can later be maintained for many generations. However, factors causing DNA damage or triggering the SOS response may cause prophage induction. Hydrogen peroxide is one of the factors that may cause induction of λ prophage, while bacterial protein OxyR is one of the crucial regulators during oxidative stress. Previous works has reported that OxyR regulates the cI gene expression by influencing the pM promoter. It was also demonstrated that hydrogen peroxide mediated induction of prophage is significantly enhanced in mutants lacking functional oxyR gene. Thus, it appears that OxyR is one of the proteins taking part in prophage maintenance in bacterial host. OxyR exists in cell in two forms: reduced (inactive) and oxidated (active). First form exists hydrogen peroxide is not present in the environment. If H2O2 is added OxyR is converted into oxidated form through formation of disulfide bond between cysteine residues Cys199 and Cys208.
In this study we investigated how presence of different forms of OxyR in bacterial cells influence prophage λ induction in presence of hydrogen peroxide. We have observed, that activity of OxyR in its oxidated form resulted in decrease in prophage induction, while presence of reduced form caused more rapid induction.
Studies on the control mechanisms of λ prophage induction may be important in bio-medical application, since certain pathogenic E. coli strains bear prophages that are members of λ family (Shiga toxin-converting phages). Those prophages encodes toxin genes that are expressed after bacteriophage enters lytic cycle. Phage λ may serve as a model in studies on biology of this phages.