Identification and evaluation of the role of the manganese efflux protein in Deinococcus radiodurans

In this study, we identified the manganese efflux protein (MntE) in D. radiodurans. The null mutant of mntE was more sensitive than the wild-type strain to manganese ions, and the growth of the mntE mutant was delayed in manganese-supplemented media. Furthermore, there was a substantial increase in the in vivo concentration of manganese ions. Consistent with these characteristics, the mntE mutant was more resistant to H2O2, ultraviolet rays, and γ-radiation. The intracellular protein oxidation (carbonylation) level of the mutant strain was remarkably lower than that of the wild-type strain.Our results indicated that dr1236 is indeed a mntE homologue and is indispensable for maintaining manganese homeostasis in D. radiodurans. The data also provide additional evidence for the involvement of intracellular manganese ions in the radiation resistance of D. radiodurans.Deinococcus radiodurans is an extreme bacterium known for its resistance to ionizing radiation (IR), ultraviolet (UV) radiation, oxidative stress, and desiccation [1,2]. It has been reported that D. radiodurans can recover from exposure to γ-radiation at 15 kGy, a dose lethal to most life forms. IR can directly damage biomacromolecules and can also produce reactive oxygen species (ROS) that can indirectly attack both proteins and DNA [3,4]. Therefore, cellular defense against ROS-induced protein and DNA damage is proposed to be important to the radiation resistance of D. radiodurans [5].Manganese plays an important role in the antioxidant systems of bacteria and can relieve the phenotypic deficit of sod-null Escherichia coli [6]. Interestingly, Daly and coworkers found that the Mn/Fe ratio of most IR-resistant bacteria is higher than that of IR-sensitive bacteria. The group also found that D. radiodurans grown in manganese-deficient medium was relatively more sensitive to IR than the bacteria grown in manganese-containing medium, suggesting that the accumulation of intracellular manganese ions can protect p