Deinococcus radiodurans is extremely resistant to ionizing radiation. How this bacterium can grow under chronic gamma radiation [50 grays (Gy) per hour] or recover from acute doses greater than 10 kGy is unknown. We show that D. radiodurans accumulates very high intracellular manganese and low iron levels compared with radiation-sensitive bacteria and that resistance exhibits a concentration-dependent response to manganous chloride [Mn(II)]. Among the most radiation-resistant bacterial groups reported, Deinococcus, Enterococcus, Lactobacillus, and cyanobacteria accumulate Mn(II). In contrast, Shewanella oneidensis and Pseudomonas putida have high iron but low intracellular manganese concentrations and are very sensitive. We propose that Mn(II) accumulation facilitates recovery from radiation injury.

Understanding biological systems and the roles of their constituents is facilitated by the ability to make quantitative, sensitive, and comprehensive measurements of how their proteome changes, e.g., in response to environmental perturbations. To this end, we have developed a high-throughput methodology to characterize an organism's dynamic proteome based on the combination of global enzymatic digestion, high-resolution liquid chromatographic separations, and analysis by Fourier transform ion cyclotron resonance mass spectrometry. The peptides produced serve as accurate mass tags for the proteins and have been used to identify with high confidence >61% of the predicted proteome for the ionizing radiation-resistant bacterium Deinococcus radiodurans. This fraction represents the broadest proteome coverage for any organism to date and includes 715 proteins previously annotated as either hypothetical or conserved hypothetical.