RecBC enzyme overproduction affects UV and gamma radiation survival of Deinococcus radiodurans

Deinococcus radiodurans recovering from the effect of acute dose of gamma (γ) radiation shows a biphasic mechanism of DNA double strands breaks repair that involves an efficient homologous recombination. However, it shows higher sensitivity to near-UV (NUV) than Escherichia coli and lacks RecBC, a DNA strand break (DSB) repair enzyme in some bacteria. Recombinant Deinococcus expressing the recBC genes of E. coli showed nearly three-fold improvements in near-UV tolerance and nearly 2 log cycle reductions in wild type γ radiation resistance. RecBC over expression effect on radiation response of D. radiodurans was independent of indigenous RecD. Loss of γ radiation tolerance was attributed to the enhanced rate of in vivo degradation of radiation damaged DNA and delayed kinetics of DSB repair during post-irradiation recovery. RecBC expressing cells of Deinococcus showed wild type response to Far-UV. These results suggest that the overproduction of RecBC competes with the indigenous mechanism of γ radiation damaged DNA repair while it supports near-UV tolerance in D. radiodurans.