New insights into the activation of Radiation Desiccation Response regulon in Deinococcus radiodurans.

The highly radiation-resistant bacterium Deinococcus radiodurans responds to gamma radiation or desiccation through the coordinated expression of genes belonging to Radiation and Desiccation Resistance/Response (RDR) regulon. RDR regulon is operated through cis-acting sequence RDRM (Radiation Desiccation Response Motif), trans-acting repressor DdrO and protease IrrE (also called PprI). The present study evaluated whether RDR regulon controls the response of D. radiodurans to various other DNA damaging stressors, to which it is resistant, such as UV rays, mitomycin C (MMC), methyl methanesulfonate (MMS), ethidium bromide (EtBr), etc. Activation of 3 RDR regulon genes (ddrB, gyrB and DR1143) was studied by tagging their promoter sequences with a highly sensitive GFP reporter. Here we demonstrated that all the DNA damaging stressors elicited activation of RDR regulon of D. radiodurans in a dose-dependent and RDRM-/IrrE-dependent manner. However, ROS-mediated indirect effects [induced by hydrogen peroxide (H2O2), methyl viologen (MV), heavy metal/metalloid (zinc or tellurite), etc.] did not activate RDR regulon. We also showed that level of activation was inversely proportional to cellular abundance of repressor DdrO. Our data strongly suggests that direct DNA damage activates RDR regulon in D. radiodurans.