Abstract

Shao Hua, Chang Shenghe*, Li Zongwei, Wang Yanping and Qin Guangyong

The radiation resistant bacterium Deinococcus radiodurans R1 possesses a high intracellular Mn/Fe concentration ratio. Non-enzymic Mn(II) in D. radiodurans acts as an antioxidant to scavenge reactive oxygen species which contributes to its extreme radioresistance. The gene dr2539 encodes a transcriptional regulator that is predicted to be involved in regulating the transportation of Mn(II) or Fe(II) in D. radiodurans R1. In this study, we constructed a dr2539disruption mutant with D. radiodurans R1 and compared them in growth rates and in intracellular Fe and Mn ions concentrations. We also investigated the phenotypes of the two strains including protease secretion and resistance to heavy metal ions, H2O2 and MV. The results showed that D. radiodurans R1 did not exhibit strong resistance to Hg(II), Ag(I), Cr(VI) and Pb(IV). Disruption of the gene dr2539 in D. radiodurans R1 resulted in an obvious growth defect in Mn-depleted medium and a remarkably-increased sensitivity to Mn(II). The disruption mutant obviously accumulated the intracellular Mn ion and raised the intracellular Mn/Fe ratio in Mn(II)-replete medium, but it had the similar intracellular Mn/Fe ratio with the wild strain in Fe(II)-replete medium. Furthermore, although the mutant accumulated high levels of intracellular Mn/Fe ratio in Mn(II)-replete medium, disruption of the gene dr2539 had no apparent effect on its resistance to H2 O2 and MV. These results suggest that the gene dr2539 in D. radiodurans R1 plays an important role in regulating the transportation of Mn(II) and the correlation between the intracellular Mn/Fe ratio and the antioxidant capacity in D. radiodurans need further study.